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A Nationwide Study of Prevalence Rates and Characteristics of 199 Chronic Conditions in Denmark

  • Michael Falk HvidbergEmail author
  • Soeren Paaske Johnsen
  • Michael Davidsen
  • Lars Ehlers
Open Access
Original Research Article
First Online:

Abstract

Background

Real-world data of disease prevalence represents an important but underutilised source of evidence for health economic modelling.

Aims

The aim of this study was to estimate nationwide prevalence rates and summarise the characteristics of 199 chronic conditions using Danish population-based health registers, to provide an off-the-shelf tool for decision makers and researchers.

Methods

The study population comprised all Danish residents aged 16 years or above on 1 January 2013 (n = 4,555,439). The study was based on the linkage of national registers covering hospital contacts, contacts with primary care (including general practitioners) and filled-in out-of-hospital prescriptions.

Results

A total of 65.6% had one or more chronic condition. The ten conditions with the highest degree of prevalence were hypertension (23.3%), respiratory allergy (18.5%), disorders of lipoprotein metabolism (14.3%), depression (10.0%), bronchitis (9.2%), asthma (7.9%), type 2 diabetes (5.3%), chronic obstructive lung disease (4.7%), osteoarthritis of the knee (3.9%) and finally osteoporosis (3.5%) and ulcers (3.5%) in joint tenth place. Characteristics by gender, age and national geographical differences were also presented.

Conclusions

A nationwide catalogue of the prevalence rates and characteristics of patients with chronic conditions based on a nationwide population is provided. The prevalence rates of the 199 conditions provide important information on the burden of disease for use in healthcare planning, as well as for economic, aetiological and other research.

Key Points for Decision Makers

Real-world evidence of disease prevalence is important for estimating the burden of disease, cost of illness and budget impact of new health technologies.

The Danish civil registration number provides a unique opportunity to link different types of register data for an individual patient, thus providing the best possible information on the actual treatment of chronic diseases.

Nationwide register-based prevalence statistics for 199 chronic diseases show, for most disease areas, a higher current treatment level than that expected from epidemiological research. In 2013, almost two-thirds of the entire Danish population aged 16 years or above either had a hospital diagnosis or had been in medical treatment for one or more chronic condition.

1 Introduction

Worldwide, the financial pressures on healthcare providers are increasing. To control the rising cost of healthcare, decision makers need access to real-world evidence of current treatment patterns [1, 2]. Real-world evidence of disease prevalence is important for estimating the burden of disease, cost of illness, and budget impact of new health technologies [3, 4]. In addition, it is important to obtain unbiased, independent documentation of disease burden, as there may be concerns with the cost-of-illness studies funded by companies [5].

The burden of chronic diseases is increasing rapidly in most countries. In Denmark, approximately 30–50% of the adult population have one or more chronic condition or long-standing illness [6, 7, 8, 9, 10]. Moreover, the burdens of chronic conditions are increasing [11, 12, 13, 14, 15, 16, 17, 18, 19, 20]. The numbers and expenditure are growing along with an ageing population, and up to 80% of total healthcare costs can be attributed to chronic conditions [21, 22, 23, 24]. Thus, the need for reliable and affordable estimates of the prevalence and disease burden of chronic conditions to guide decision-making in healthcare is increasing [24, 25, 26].

There are different ways to measure the prevalence of chronic conditions, varying from community-based health surveys and screening investigations to register-based studies. The choice of definitions and methods naturally affects which patients are included and hence the prevalence [27, 28].

The Scandinavian countries have an established tradition of documenting the diseases and hospital treatments of the entire population in registers; however, the registers have primarily been used to study individual conditions rather than to assess the total burden of chronic conditions [7, 24, 26, 29, 30, 31, 32, 33, 34], or to forecast drug spending to help with decision-making [35, 36].

The aim of the present study was to estimate the national prevalence rates and to summarise the characteristics of 199 chronic conditions using the complete Danish population aged 16 and above. To the best of the authors’ knowledge, the current study is the most comprehensive, independent register-based attempt to estimate the full-population prevalence-based disease burden of chronic diseases.

2 Methods

2.1 Study Population

The nationwide study population and cohort consisted of 4,555,439 Danish residents who were alive and aged 16 years or above on 1 January 2013, of which 49.2% were men.

2.2 The Registers

In Scandinavian countries, general practitioners (GPs) and hospitals have a long-standing tradition of reporting diseases, treatments, medications and other treatment-related information. This is done at the micro level for national health registers. Register data are collected mostly for public administration such as claims and management, surveillance and control functions [37]. The comprehensiveness, scope and population completeness are unique to Denmark and other Scandinavian countries, enabling individual linkage across registers by means of the individual personal identification number assigned to each person [38]. The main register used was the Danish National Patient Register (NPR) [39], including the Danish Psychiatric Central Research Register [40], containing treating-physician-reported International Statistical Classification of Diseases, 10th Revision (ICD-10) hospital diagnoses. Moreover, to ensure the inclusion of patients not treated in hospitals, the National Health Service Register (NHSR) [41] and National Prescription Registry (TNPR) [42] were included in the study, since the NPR did not include diagnosis data from private specialist doctors or GPs. The NHSR contains data collected primarily for administrative purposes from health contractors in primary healthcare. It includes information about citizens, providers and health services, but minimal clinical information. Furthermore, the TNPR, comprising all prescribed and distributed medicines outside hospitals, was included to ensure the best possible identification of conditions and the representativeness thereof by clinical recommendation. All registers had a unique civil registration number for each person; furthermore, birth date, gender and other information were derived from the Danish Civil Registration System [43]. The registers used are described in more detail in other studies [44, 45]. Table 1 summarises the details of the registers used.
Table 1

The registers used and characteristics of the selected population in summary

Registry

Years of registry use

Population

Contains

The National Patient Register [39]

1994–2012

All somatic hospital-treated in/outpatients. Primary, secondary and additional diagnosis for patients aged 16 years or above

ICD-10 diagnosis codes for all public and private hospital-treated patients for every contact and treatment for the entire population as well as a civil registration number. Furthermore, data from all hospital treatments/procedures/operations for all hospital-treated patients as well as a civil registration number

The Danish Psychiatric Central Research Register [40]

1995–2012

All psychiatric hospital-treated in/outpatients. Primary, secondary and additional diagnosis for patients aged 16 years or above

ICD-10 diagnosis codes for all public hospital-treated patients for every contact and treatment for the entire population as well as a civil registration number. No private psychiatric hospital exists

The National Health Service Register [41]

2000–2012

All patients in primary care aged 16 years or above

All GP services for whole population and every consultation based on civil registration number. The register does not contain information on diagnosis, but many services are disease-specific and can thus be used for identifying chronic conditions

The Danish National Prescription Registry [42]

1995–2012

All patients in primary care with a prescription who are aged 16 years or above

All Danish medicine prescriptions sold for the entire population using 6-digit ATC codes as well as a civil registration number

The Danish Civil Registration System [43]

2013

Whole population aged 16 years or above resident in Denmark on 1 January 2014

Data regarding birth date, age, gender, etc. for the entire population as well as a civil registration number

ATC Anatomical Therapeutic Chemical Classification System, GP general practitioner, ICD-10 International Statistical Classification of Diseases, 10th Revision

2.3 The Definition of a ‘Chronic Condition’, Clinical Ratification and Review

A thorough description of the distinct phases and methods used are provided elsewhere [44, 45, 46]. In short, a ‘chronic condition’ was defined in line with previous studies, i.e. the ‘condition had lasted or was expected to last twelve or more months and resulted in functional limitations and/or the need for functional limitations and/or the need for ongoing medical care’ [47, 48, 49]. An expert panel consisting of professors, medical specialists and other experts from Aalborg University, the Clinical Institute of Aalborg University at Aalborg University Hospital, the Department of Clinical Epidemiology at Aarhus University Hospital, and others was consulted using the Delphi method in order to identify which of the approximately 22,000 ICD-10 codes and conditions could be considered ‘chronic’ based on the definition [44]. The ICD-10 codes were aggregated to 199 conditions, yet several conditions included subgroups of ICD-10 codes; thus, some consequently contained multiple conditions within the same disease area. Subsequently, all ICD-10 conditions considered chronic by definition were included in the study in pursuit of comprising the full-population burden of chronic conditions. Consequently, the 199 conditions consisted of several ICD-10 codes and thus groups of illnesses.

2.4 Data Collection: The Basis of the Data Algorithms

Since many chronic conditions last longer than the defined 12 months, but do not last for a lifetime, the varying ‘chronicity’ of conditions was divided into four groups of severity [44]:

  • Category I: stationary to progressive chronic conditions (no time limit equals inclusion time going back from the time of interest for as long as valid data were available. In the current study, this starting point was defined by the introduction of the ICD-10 diagnosis coding in Denmark, in 1994).

  • Category II: stationary to diminishing chronic conditions (10 years from register inclusion time to the time of interest).

  • Category III: diminishing chronic conditions (5 years from register inclusion time to the time of interest).

  • Category IV: borderline chronic conditions (2 years from register inclusion time to the time of interest).

The above four categories were designed to include the different chronic conditions when registers covered several years and still have the best possible clinical certainty that the conditions were still existing at the fixed time point of 1 January 2013. All 199 chronic conditions were divided into one of the four categories by medical specialists and experts. An algorithm was created for data collection based on the four categories, as seen in Fig. 1 for all 199 conditions and coherent ICD-10 codes. However, 35 of the 199 chronic conditions were not considered by experts to be properly representative using solely NPR diagnosis data. Thus, they created more complex algorithms using several registers besides diagnosis data, ranging from medicine and hospital treatments to GP services. For example, medicine and coherent indication codes were used to identify people with depression without a hospital diagnosis, and only when the indication codes identified the medicine used for depression, and not others such as pain treatment, etc. The same applied to GP services indicating, for example, diabetes or chronic obstructive lung disease (COPD) treatment, etc., where no hospital diagnosis was found. The details of all 199 unique definitions, their categorisation into one of the four categories and algorithms for replication can be found elsewhere [44, 45].
Fig. 1

The four categories of chronicity and the inclusion time periods

2.5 Statistical Analysis

Prevalence estimates were calculated in both per cent and per 1000 subjects; the proportion was calculated as the number of conditions identified divided by the total number of residents aged 16 years or above alive on 1 January 2013 (n =4,555,439) multiplied by either 100 or 1000. Thus, prevalence was calculated from a specific point in time, based on the above inclusion time periods back in time for each condition. See Fig. 1 or further details in the literature [44].

The prevalence proportions for all conditions were stratified and presented by age and sex for use by, for example, local authorities, health planners and national researchers.

Direct standardisation of age, gender and education based on the national average (i.e. using Denmark as the standard/reference population for age, gender and education) [50] was applied to illustrate differences free of basic socio-economic effects (presented in brackets in Tables 2 and 3 and the electronic supplementary material). The gender and age (10-year intervals) variables were obtained from the Danish Civil Registration System [43], and the educational variables were obtained from the Population Education Register using Danish Education Nomenclature (DUN) classification [51].

Finally, tables were stratified geographically in the five national regions, and the mean age and standard deviation (SD) for each condition were calculated, but due to size and relevance for the international reader, geographical regions, mean age and SDs are presented in the electronic supplementary material.

All data management and data analysis were performed in SAS 9.4 (from Statistics Denmark’s research servers).

3 Results

3.1 The Prevalence Rates

The population’s full burden of chronic disease, with all the chronic conditions summarised, was 65.6% (see Table 2 or Table 3). The ten most prevalent conditions were hypertension (23.3%), respiratory allergy (18.5%), disorders of lipoprotein metabolism (14.3%), depression (10.0%), bronchitis (9.2%), asthma (7.9%), type 2 diabetes (5.3%), COPD (4.7%), osteoarthritis of the knee (3.9%) and osteoporosis (3.5%)/ulcer (3.5%); see the overview of conditions solely by overall disease groups in Table 2 and all 199 conditions in Table 3.
Table 2

Overview of disease prevalence in Denmark: number of patients, prevalence rate (per 1000), age and gender (per cent within gender) of disease groups of conditions and chosen medicine for Denmark at 1 January 2013

Name of condition

ICD-10 code/definition

Number and prevalence

Denmark

Men

Age 16–44 (per 1000)

Age 45–74 (per 1000)

Age 75 + (per 1000)

N

Per 1000 (standardised)

Per cent

B—Viral hepatitis and human immunodeficiency virus (HIV) disease

B18, B20–B24

8813

1.9

(2.0)

65.3

1.8

2.4

0.3

C—Malignant neoplasms

C00–C99; D32–D33; D35.2–D35.4; D42–D44

229,331

50.3

(50.4)

43.3

10.2

69.4

155.8

D—In situ and benign neoplasms, and neoplasms of uncertain or unknown behaviour and diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism

D00–D09; D55–D59; D60–D67; D80–D89

116,560

25.6

(25.7)

36.3

13.2

27.3

80.1

E—Endocrine, nutritional and metabolic diseases

E00–E14; E20–E29; E31–35; E70–E78; E84–E85; E88–E89

877,433

192.6

(192.7)

45.6

43.5

279.6

501.4

G—Diseases of the nervous system

G00–G14; G20–G32; G35–G37; G40–47; G50–64; G70–73; G80–G83; G90–G99

561,054

123.2

(123.5)

40.1

70.6

162.2

188.6

H—Diseases of the eye and adnexa and diseases of the ear and mastoid process

H02–H06; H17–H18; H25–H28; H31–H32; H34–H36; H40–55; H57; H80, H810; H93, H90–H93

448,176

98.4

(98.6)

47.5

25.6

112.6

394.4

I—Diseases of the circulatory system

I05–I06; I10–28; I30–33; I36–141; I44–I52; I60–I88; I90–I94; I96–I99

1,254,427

275.4

(275.5)

45.3

73.3

381.5

753.9

J—Diseases of the respiratory system

J30.1; J40–J47; J60–J84; J95, J97–J99

1,210,598

265.7

(266.3)

42.1

209.3

298.8

381.9

K—Diseases of the digestive system

K25–K27; K40, K43, K50–52; K58–K59; K71–K77; K86–K87

329,337

72.3

(72.6)

44.7

41.3

86.3

157.4

L—Diseases of the skin and subcutaneous tissue

L40

65,469

14.4

(14.5)

47.8

7.9

19.3

21.7

M—Diseases of the musculoskeletal system and connective tissue

M01–M25; M30–M36; M40–M54; M60.1–M99

1,032,808

226.7

(227.1)

42.2

113.2

291.2

470.5

N—Diseases of the genitourinary system

N18

20,162

4.4

(4.5)

59.4

1.0

4.8

20.0

Q—Congenital malformations, deformations and chromosomal abnormalities

Q00–Q56; Q60–Q99

124,898

27.4

(27.5)

41.7

33.9

23.2

16.2

F—Mental and behavioural disorders

F00–99

683,194

150.0

(150.7)

41.0

135.2

150.2

223.7

Having one or more chronic condition

 

2,989,441

656.2

(657.2)

45.5

480.5

771.5

953.9

Mean number of chronic conditions (std. dev)

 

2.2 (2.8)

–

–

2.0 (2.6)

1.1 (1.6)

2.7 (2.8)

5.3 (3.6)

 Depression medicinec,**

ATC: N06A

529,918

116.3

(116.7)

36.3

88.7

126.9

201.9

 Antipsychotic medicinec,**

ATC: N05A

138,625

30.4

(30.6)

45.7

26.1

31.9

44.8

 Indication prescribed anxiety medicinec,**

All prescriptions with either indication code 163 (for anxiety) or 371 (for anxiety, addictive)

102,568

22.5

(22.6)

34.5

19.9

23.7

30.1

 Heart failure medicationc,**

ATC: C01AA05, C03, C07 or C09A with indication code 430 (for heart failure)

7468

1.6

(1.7)

64.6

0.1

2.0

7.5

 Ischaemic heart medicationc,**

ATC: C01A, C01B, C01D, C01E

129,484

28.4

(28.5)

51.8

1.4

32.0

147.3

All of the five types of medicine above

 

688,006

151.0

(151.6)

40.4

100.2

166.1

331.1

Standardised rates or standard devitions in brackets

See table with 10-year age intervals in Supplementary Material 2 in the electronic supplementary matertial

Conditions marked ‘A’ overlap with other conditions and are thus not counted twice [44]

ATC Anatomical Therapeutic Chemical Classification System, ICD-10 International Statistical Classification of Diseases, 10th Revision

cComplex defined conditions; see reference for further details [44]

**Two-year prevalence

Table 3

Disease prevalence of 199 chronic conditions: number of patients treated, prevalence rate (per 1000), age and gender (per cent within gender) of all conditions and chosen medicine for Denmark at 1 January 2013

No.

Name of condition

ICD-10 code/definition

Number and prevalence

Denmark

Men

Age 16–44 (per 1000)

Age 45–74 (per 1000)

Age 75+ (per 1000)

N

Per 1000 (standardised)

Per cent

 

B—Viral hepatitis and human immunodeficiency virus [HIV] disease

B18, B20–B24

8813

1.9

(2.0)

65.3

1.8

2.4

0.3

1

Chronic viral hepatitis

B18

4584

1.0

(1.0)

60.1

1.0

1.2

0.1

2

Human immunodeficiency virus [HIV] disease

B20–24

4229

0.9

(0.9)

71.0

0.8

1.2

0.1

 

C—Malignant neoplasms

C00–C99; D32–D33; D35.2–D35.4; D42–D44

229,331

50.3

(50.4)

43.3

10.2

69.4

155.8

3

Malignant neoplasms of other and unspecified localizations

C00–C14; C30–C33; C37–C42; C45–C49; C69; C73–74; C754–C759

20,557

4.5

(4.6)

53.5

1.3

6.6

10.1

4

Malignant neoplasms of digestive organs

C15–C17; C22–C26

4839

1.1

(1.1)

59.5

0.1

1.6

3.4

5

Malignant neoplasm of colon

C18

18,826

4.1

(4.1)

47.0

0.2

4.9

20.3

6

Malignant neoplasms of rectosigmoid junction, rectum, anus and anal canal

C19–C21

10,680

2.3

(2.3)

55.4

0.1

3.2

9.5

7

Malignant neoplasm of bronchus and lung

C34

14,762

3.2

(3.3)

49.4

0.2

4.8

10.6

8

Malignant melanoma of skin

C43

19,636

4.3

(4.3)

42.6

2.0

5.7

9.0

9

Other malignant neoplasms of skin

C44

15,597

3.4

(3.4)

51.2

0.3

3.9

16.7

10

Malignant neoplasm of breast

C50

50,687

11.1

(11.1)

0.7

1.0

17.6

29.5

11

Malignant neoplasms of female genital organs

C51–C52; C56–C58

7245

1.6

(1.6)

–

0.3

2.4

3.9

12

Malignant neoplasm of cervix uteri, corpus uteri and part unspecified

C53–C55

11,608

2.5

(2.5)

0.0

0.7

3.5

7.1

13

Malignant tumour of male genitalia

C60, C62–C63

5194

1.1

(1.1)

99.9

1.2

1.2

0.7

14

Malignant neoplasm of prostate

C61

26,697

5.9

(5.9)

100.0

0.0

7.5

27.0

15

Malignant neoplasms of urinary tract

C64–C68

10,319

2.3

(2.3)

71.2

0.1

2.9

9.9

16

Brain cancerc

C71, C75.1–C75.3, D33.0–D33.2, D35.2–D35.4, D43.0–D43.2, D44.3–D44.5 (brain). C70, D32, D42 (brain membrane). C72, D33.3–D33.9, D43.3–D43.9 (cranial nerve, spinal cord)

15,310

3.4

(3.4)

52.9

1.4

4.7

6.2

17

Malignant neoplasms of ill-defined, secondary and unspecified sites, and of independent (primary) multiple sites

C76–C80, C97

25,619

5.6

(5.6)

43.0

1.2

8.4

14.0

18

Malignant neoplasms, stated or presumed to be primary, of lymphoid, haematopoietic and related tissue

C81–C96

19,712

4.3

(4.3)

54.4

1.5

5.6

12.4

 

D—In situ and benign neoplasms, and neoplasms of uncertain or unknown behaviour and diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism

D00–D09; D55–D59; D60–D67; D80–D89

116,560

25.6

(25.7)

36.3

13.2

27.3

80.1

19

In situ neoplasms

D00–D09

19,810

4.3

(4.4)

20.0

2.5

5.5

7.9

20

Haemolytic anaemias

D55–D59

3055

0.7

(0.7)

33.7

0.7

0.6

1.2

21

Aplastic and other anaemias

D60–D63

14,918

3.3

(3.3)

40.2

0.9

3.3

15.0

22

Other anaemias

D64

46,613

10.2

(10.3)

38.7

2.3

9.7

53.1

23

Coagulation defects, purpura and other haemorrhagic conditions

D65–D69

25,376

5.6

(5.6)

37.4

5.2

5.7

7.1

24

Other diseases of blood and blood-forming organs

D70–D77

8896

2.0

(2.0)

43.5

1.0

2.6

3.6

25

Certain disorders involving the immune mechanism

D80–D89

7660

1.7

(1.7)

50.8

1.4

2.0

1.3

 

E—Endocrine, nutritional and metabolic diseases

E00–E14; E20–E29; E31–35; E70–E78; E84–E85; E88–E89

877,433

192.6

(192.7)

45.6

43.5

279.6

501.4

26

Diseases of the thyroidc

E00–E04, E06, E07

131,908

29.0

(29.0)

15.9

11.3

39.1

66.2

27

Thyrotoxicosisc

E05

41,374

9.1

(9.0)

18.3

3.8

10.8

26.7

28

Diabetes type 1c

E10

23,062

5.1

(5.1)

57.9

4.9

5.6

3.5

29

Diabetes type 2c

E11

242,177

53.2

(53.3)

53.0

8.5

77.9

152.1

30

Diabetes othersc

E12–E14

1117

0.2

(0.2)

48.6

0.2

0.3

0.5

31

Disorders of other endocrine glands

E20–E35, except E30

28,650

6.3

(6.4)

28.6

6.5

5.6

8.9

32

Metabolic disorders

E70–E77; E79–E83; E85, E88–E89;

23,690

5.2

(5.2)

36.6

3.7

6.1

8.2

33

Disturbances in lipoprotein circulation and other lipidsc

E78

652,242

143.2

(143.1)

51.1

11.8

221.2

408.1

34

Cystic fibrosisc

E84

947

0.2

(0.2)

41.9

0.3

0.1

0.1

 

G—Diseases of the nervous system

G00–G14; G20–G32; G35–G37; G40–47; G50–64; G70–73; G80–G83; G90–G99

561,054

123.2

(123.5)

40.1

70.6

162.2

188.6

35

Inflammatory diseases of the central nervous system

G00–G09

7642

1.7

(1.7)

50.1

1.3

2.0

2.2

36

Systemic atrophies primarily affecting the central nervous system and other degenerative diseases

G10–G14, G30–G32

10,401

2.3

(2.3)

46.8

0.4

2.2

12.1

37

Parkinson’s diseasec

G20, G21, G22, F02.3

57,583

12.6

(12.6)

43.7

4.1

16.3

37.3

38

Extrapyramidal and movement disorders

G23–G26

10,837

2.4

(2.4)

41.8

1.1

2.9

6.4

39

Sclerosis

G35

13,284

2.9

(2.9)

30.6

1.9

4.2

1.5

40

Demyelinating diseases of the central nervous system

G36–G37

4571

1.0

(1.0)

34.7

0.9

1.3

0.4

41

Epilepsyc

G40–G41

61,695

13.5

(13.6)

48.2

9.7

16.0

20.3

42

Migrainec

G43

149,866

32.9

(33.0)

18.6

24.9

44.1

15.6

43

Other headache syndromes

G44

16,469

3.6

(3.6)

35.9

4.0

3.6

1.8

44

Transient cerebral ischaemic attacks and related syndromes and vascular syndromes of brain in cerebrovascular diseases

G45–G46

43,977

9.7

(9.7)

53.5

1.1

12.7

37.6

45

Sleep disorders

G47

36,806

8.1

(8.1)

73.5

4.1

12.6

5.0

46

Disorders of trigeminal nerve and facial nerve disorders

G50–G51

21,488

4.7

(4.7)

43.0

2.8

6.0

7.4

47

Disorders of other cranial nerves, cranial nerve disorders in diseases classified elsewhere, nerve root and plexus disorders and nerve root and plexus compressions in diseases classified elsewhere

G52–G55

12,429

2.7

(2.7)

48.9

1.3

4.0

3.6

48

Mononeuropathies of upper limb

G56

122,395

26.9

(26.9)

37.2

12.6

39.1

36.5

49

Mononeuropathies of lower limb, other mononeuropathies and mononeuropathy in diseases classified elsewhere

G57–G59

18,627

4.1

(4.1)

43.8

1.9

6.1

5.0

50

Polyneuropathies and other disorders of the peripheral nervous system

G60–G64

30,289

6.6

(6.7)

56.4

1.7

9.3

18.2

51

Diseases of myoneural junction and muscle

G70–G73

5758

1.3

(1.3)

47.7

0.9

1.5

1.6

52

Cerebral palsy and other paralytic syndromes

G80–G83

14,410

3.2

(3.2)

53.9

2.9

3.5

3.2

53

Other disorders of the nervous system

G90–G99

44,394

9.7

(9.8)

46.4

5.9

12.1

17.0

 

H—Diseases of the eye and adnexa and diseases of the ear and mastoid process

H02–H06; H17–H18; H25–H28; H31–H32; H34–H36; H40–55; H57; H80, H810; H93, H90–H93

448,176

98.4

(98.6)

47.5

25.6

112.6

394.4

54

Disorders of eyelid, lacrimal system and orbit

H02–H06

13,191

2.9

(2.9)

37.3

0.9

4.0

7.5

55

Corneal scars and opacities

H17

2173

0.5

(0.5)

58.1

0.2

0.5

1.3

56

Other disorders of cornea

H18

9473

2.1

(2.1)

43.5

1.0

2.1

7.4

57

Diseases of the eye lens (cataracts)

H25–H28

68,009

14.9

(15.1)

40.5

0.5

15.6

84.8

58

Disorders of the choroid and retina

H31–H32

1900

0.4

(0.4)

48.3

0.2

0.5

1.1

59

Retinal vascular occlusions

H34

10,358

2.3

(2.3)

50.8

0.2

2.6

11.4

60

Other retinal disorders

H35

68,485

15.0

(15.1)

40.2

1.6

13.0

93.7

61

Retinal disorders in diseases classified elsewhere

H36

19,279

4.2

(4.3)

58.7

1.7

6.1

7.4

62

Glaucomac

H40–H42

67,310

14.8

(14.9)

43.5

1.2

16.2

76.4

63

Disorders of the vitreous body and globe

H43–H45

7572

1.7

(1.7)

44.6

0.7

2.4

3.1

64

Disorders of optic nerve and visual pathways

H46–H48

6184

1.4

(1.4)

39.0

1.2

1.6

1.4

65

Disorders of ocular muscles, binocular movement, accommodation and refraction

H49–H52

18,247

4.0

(4.0)

45.4

4.3

3.9

2.8

66

Visual disturbances

H53

22,232

4.9

(4.9)

45.7

2.6

5.9

11.1

67

Blindness and partial sight

H54

6614

1.5

(1.5)

44.4

0.6

1.5

5.6

68

Nystagmus and other irregular eye movements and other disorders of eye and adnexa

H55, H57

11,133

2.4

(2.5)

40.3

1.7

3.0

3.7

69

Otosclerosis

H80

10,360

2.3

(2.3)

35.7

0.8

3.1

5.4

70

Ménière’s diseasec

H810

10,003

2.2

(2.2)

43.0

0.4

3.0

7.3

71

Other diseases of the inner ear

H83

29,865

6.6

(6.3)

91.8

0.6

9.0

24.5

72

Conductive and sensorineural hearing loss

H90

43,238

9.5

(9.6)

48.7

3.7

11.3

29.5

73

Other hearing loss and other disorders of ear, not elsewhere classified

H910, H912, H913, H918, H930, H932, H933

8306

1.8

(1.8)

53.0

0.7

2.3

5.2

74

Presbycusis (age-related hearing loss)

H911

80,659

17.7

(17.6)

48.9

0.4

9.6

147.4

75

Hearing loss, unspecified

H919

87,806

19.3

(19.3)

55.3

3.0

24.5

74.5

76

Tinnitus

H931

40,124

8.8

(8.7)

58.4

2.5

13.4

17.5

77

Other specified disorders of ear

H938

20,537

4.5

(4.4)

48.1

0.8

5.9

16.1

 

I—Diseases of the circulatory system

I05–I06; I10–28; I30–33;I36–141; I44–I52; I60–I88; I90–I94; I96–I99

1,254,427

275.4

(275.5)

45.3

73.3

381.5

753.9

78

Aortic and mitral valve diseasec

I05, I06, I34, I35

30,123

6.6

(6.6)

50.9

0.7

6.4

37.7

79

Hypertensive diseasesc

I10–I15

1,060,046

232.7

(232.7)

44.6

41.8

330.8

695.8

80

Heart failurec

I11.0, I13.0, I13.2, I42.0, I42.6, I42.7, I42.9, I50.0, I50.1, I50.9

37,540

8.2

(8.3)

63.5

0.7

9.5

40.3

80A

Ischaemic heart diseases

I20–I25

139,173

30.6

(30.7)

60.2

2.6

41.8

114.5

81

Angina pectoris

I20

78,476

17.2

(17.3)

58.4

1.6

25.7

53.0

82

Acute myocardial infarction and

subsequent myocardial infarction

I21–I22

36,654

8.0

(8.1)

66.6

0.7

11.1

29.8

83

AMI complex/other

I23–I24

2969

0.7

(0.7)

61.3

0.1

0.9

2.3

84

Chronic ischaemic heart disease

I25

84,592

18.6

(18.6)

64.7

0.8

23.8

81.4

85

Pulmonary heart disease and diseases of pulmonary circulation

I26–I28

15,352

3.4

(3.4)

44.8

1.0

3.8

13.0

86

Acute pericarditis

I30

5563

1.2

(1.2)

73.1

1.0

1.4

1.3

87

Other forms of heart disease

I31–I43, except I34–I35 and I42

8,119

1.8

(1.8)

60.5

0.7

2.1

5.4

88

Atrioventricular and left bundle branch block

I44

14,604

3.2

(3.2)

58.7

0.4

2.7

20.0

89

Other conduction disorders

I45–46

11,823

2.6

(2.6)

59.6

1.0

2.8

9.5

90

Paroxysmal tachycardia

I47

39,510

8.7

(8.7)

48.1

3.3

11.0

23.9

91

Atrial fibrillation and flutter

I48

112,342

24.7

(24.7)

57.2

1.7

26.5

132.0

92

Other cardiac arrhythmias

I49

34,418

7.6

(7.6)

47.9

2.2

8.7

28.8

93

Complications and ill-defined descriptions of heart disease and other heart disorders in diseases classified elsewhere

I51–52

7337

1.6

(1.6)

50.3

0.6

1.8

5.7

94

Stroke

I60, I61,I63–I64, Z501 (rehabilitation)

72,606

15.9

(16.0)

54.2

1.6

19.8

68.7

95

Cerebrovascular diseases

I62, I65–I68

17,308

3.8

(3.8)

51.1

0.8

4.9

13.3

96

Sequelae of cerebrovascular disease

I69

50,952

11.2

(11.2)

52.5

0.8

12.7

55.9

97

Atherosclerosis

I70

32,064

7.0

(7.0)

53.6

0.4

8.3

34.2

98

Aortic aneurysm and aortic dissection

I71

10,296

2.3

(2.3)

72.2

0.1

2.6

11.2

99

Diseases of arteries, arterioles and capillaries

I72, I74, I77–I79

11,830

2.6

(2.6)

45.6

1.0

3.4

6.2

100

Other peripheral vascular diseases

I73

28,508

6.3

(6.3)

54.8

0.7

8.3

24.4

101

Phlebitis, thrombosis of the portal vein and others

I80–I82

37,388

8.2

(8.3)

45.5

3.5

10.2

22.2

102

Varicose veins of lower extremities

I83

23,530

5.2

(5.2)

30.6

3.2

6.8

6.6

103

Haemorrhoidsc

I84

74,285

16.3

(16.3)

40.1

14.5

17.5

19.0

104

Oesophageal varices (chronic), varicose veins of other sites, other disorders of veins, non-specific lymphadenitis, other non-infective disorders of lymphatic vessels and lymph nodes and other and unspecified disorders of the circulatory system

I85–I99, except I89 and I95

15,194

3.3

(3.3)

52.6

2.2

3.9

6.1

 

J—Diseases of the respiratory system

J30.1; J40–J47; J60–J84; J95, J97–J99

1,210,598

265.7

(266.3)

42.1

209.3

298.8

381.9

105

Respiratory allergyc

J30, except J30.0

841,685

184.8

(185.2)

41.0

154.0

204.3

240.3

105A

Chronic lower respiratory diseasesc

J40–J43, J47

418,120

91.8

(92.0)

39.8

57.8

112.8

156.3

106

Bronchitis, not specified as acute

or chronic, simple and

mucopurulent chronic bronchitis

and unspecified chronic bronchitis

J40–J42

12,790

2.8

(2.8)

43.6

0.4

3.5

11.3

107

Emphysema

J43

5557

1.2

(1.2)

51.1

0.2

1.7

3.7

108

Chronic obstructive lung disease (COPD)c

J44, J96, J13–J18

216,184

47.5

(47.6)

45.0

17.6

60.6

131.4

109

Asthma, status asthmaticusc

J45–J46

361,129

79.3

(79.4)

42.1

64.2

86.5

118.4

110

Bronchiectasis

J47

4362

1.0

(1.0)

35.0

0.3

1.4

2.2

111

Other diseases of the respiratory system

J60–J84; J95, J97–J99

21,993

4.8

(4.9)

52.5

1.5

6.2

14.6

 

K—Diseases of the digestive system

K25–K27; K40, K43, K50–52; K58–K59; K71–K77; K86–K87

329,337

72.3

(72.6)

44.7

41.3

86.3

157.4

112

Ulcersc

K25–K27

157,379

34.5

(34.8)

43.2

15.3

42.4

91.9

113

Inguinal hernia

K40

25,032

5.5

(5.5)

88.7

2.1

7.7

11.5

114

Ventral hernia

K43

7941

1.7

(1.7)

44.7

0.7

2.5

3.3

115

Crohn’s diease

K50

18,913

4.2

(4.2)

41.4

4.4

4.1

3.4

116

Ulcerative colitis

K51

29,538

6.5

(6.5)

45.2

5.4

7.2

8.2

117

Other non-infective gastroenteritis and colitis

K52

20,844

4.6

(4.6)

35.5

2.6

5.0

12.8

118

Irritable bowel syndrome (IBS)

K58

37,593

8.3

(8.3)

29.9

7.5

9.0

8.4

119

Other functional intestinal disorders

K59

51,933

11.4

(11.5)

37.0

6.5

11.8

34.1

120

Diseases of liver, biliary tract and pancreas

K71–K77; K86–K87

26,956

5.9

(6.0)

48.6

2.4

8.8

8.5

 

L—Diseases of the skin and subcutaneous tissue

L40

65,469

14.4

(14.5)

47.8

7.9

19.3

21.7

121

Psoriasisc

L40

65,469

14.4

(14.5)

47.8

7.9

19.3

21.7

 

M—Diseases of the musculoskeletal system and connective tissue

M01–M25; M30–M36; M40–M54; M60.1–M99

1,032,808

226.7

(227.1)

42.2

113.2

291.2

470.5

122

Infectious arthropathies

M01–M03

9402

2.1

(2.1)

49.7

1.8

2.3

2.1

122A

Inflammatory polyarthropathies and ankylosing spondylitisc

M05–M14, M45

165,944

36.4

(36.5)

51.7

12.7

50.4

84.9

123

Rheumatoid arthritisc

M05, M06, M07.1, M07.2, M07.3, M08, M09

77,345

17.0

(17.0)

34.2

8.1

23.1

30.5

124

Inflammatory polyarthropathies

– except rheumatoid arthritisc

M074–M079, M10–M14, M45

115,945

25.5

(25.5)

58.3

7.9

35.4

63.3

125

Polyarthrosis [arthrosis]

M15

16,935

3.7

(3.7)

20.8

0.2

5.4

12.6

126

Coxarthrosis [arthrosis of hip]

M16

104,115

22.9

(22.7)

43.3

2.0

26.8

108.1

127

Gonarthrosis [arthrosis of knee]

M17

178,811

39.3

(39.4)

44.2

5.0

58.6

113.5

128

Arthrosis of first carpometacarpal joint and other arthrosis

M18–M19

91,101

20.0

(20.1)

41.7

4.2

31.0

43.4

129

Acquired deformities of fingers and toes

M20

55,730

12.2

(12.3)

21.3

5.5

17.9

17.1

130

Other acquired deformities of limbs

M21

20,584

4.5

(4.5)

34.9

2.7

5.8

6.9

131

Disorders of patella (knee cap)

M22

38,999

8.6

(8.6)

38.0

13.7

5.0

0.6

132

Internal derangement of knee

M230, M231, M233, M235, M236, M238

9192

2.0

(2.0)

55.6

2.8

1.5

0.4

133

Derangement of meniscus due to old tear or injury

M232

36,374

8.0

(8.0)

53.6

6.9

10.2

2.5

134

Internal derangement of knee, unspecified

M239

28,206

6.2

(6.2)

50.0

6.9

6.3

2.3

135

Other specific joint derangements

M24, except M240–M241

5923

1.3

(1.3)

57.2

1.9

0.9

0.5

136

Other joint disorders, not elsewhere classified

M25

12,043

2.6

(2.7)

34.7

2.3

3.1

1.9

137

Systemic connective tissue disorders

M30–M36, except M32,M34

42,631

9.4

(9.4)

24.7

4.2

10.0

32.3

138

Systemic lupus erythematosus

M32

3376

0.7

(0.7)

12.9

0.5

1.0

0.7

139

Dermatopolymyositis

M33

1137

0.2

(0.2)

39.8

0.1

0.4

0.4

140

Systemic sclerosis

M34

1675

0.4

(0.4)

21.0

0.1

0.6

0.5

141

Kyphosis, lordosis

M40

4160

0.9

(0.9)

47.7

0.7

1.1

0.7

142

Scoliosis

M41

17,686

3.9

(3.9)

31.9

5.0

2.7

4.3

143

Spinal osteochondrosis

M42

8034

1.8

(1.8)

63.4

1.4

2.2

1.0

144

Other deforming dorsopathies

M43

23,756

5.2

(5.3)

42.4

2.2

7.3

9.9

145

Other inflammatory spondylopathies

M46

7086

1.6

(1.6)

45.5

1.1

1.9

2.0

146

Spondylosis

M47

61,999

13.6

(13.6)

45.9

2.4

21.2

31.4

147

Other spondylopathies and spondylopathies in diseases classified elsewhere

M48, M49

50,805

11.2

(11.2)

44.8

1.1

14.7

43.7

148

Cervical disc disorders

M50

11,476

2.5

(2.5)

46.4

1.5

3.8

1.2

149

Other intervertebral disc disorders

M51

40,161

8.8

(8.9)

49.4

6.4

11.4

7.6

150

Other dorsopathies, not elsewhere classified

M53

7246

1.6

(1.6)

40.9

1.4

1.9

1.2

151

Dorsalgia

M54

40,780

9.0

(9.0)

42.9

7.3

10.0

11.9

152

Soft tissue disorders

M60–M63, except M60.0

13,422

2.9

(3.0)

28.6

3.2

2.8

2.4

153

Synovitis and tenosynovitis

M65

19,104

4.2

(4.2)

37.5

3.1

5.4

3.8

154

Disorders of synovium and tendon

M66–68

19,669

4.3

(4.3)

41.7

4.7

4.3

2.1

155

Soft tissue disorders related to use, overuse and pressure

M70

11,090

2.4

(2.4)

42.4

1.6

3.0

3.4

156

Fibroblastic disorders

M72

43,600

9.6

(9.6)

63.7

2.3

14.2

22.6

157

Shoulder lesions

M75

58,112

12.8

(12.7)

50.3

7.2

19.0

8.6

158

Enthesopathies of lower limb, excluding foot

M76

11,223

2.5

(2.5)

49.4

2.7

2.6

0.9

159

Other enthesopathies

M77

10,500

2.3

(2.3)

40.4

1.9

2.9

1.0

160

Rheumatism, unspecified

M790

6852

1.5

(1.5)

13.7

0.7

2.3

1.2

161

Myalgia

M791

10,168

2.2

(2.2)

36.8

1.4

2.9

3.0

162

Other soft tissue disorders, not elsewhere classified

M792– M794; M798–M799

7939

1.7

(1.7)

36.9

1.5

2.0

1.7

163

Other soft tissue disorders, not elsewhere classified: pain in limb

M796

22,201

4.9

(4.9)

41.5

3.9

5.5

6.7

164

Fibromyalgia

M797

3399

0.7

(0.7)

4.5

0.6

1.0

0.3

165

Osteoporosisc

M80–M81

158,813

34.9

(34.8)

15.3

0.7

43.5

163.6

166

Osteoporosis in diseases classified elsewhere

M82

1007

0.2

(0.2)

35.2

0.1

0.3

0.7

167

Adult osteomalacia and other disorders of bone density and structure

M83, M85, except M833

43,271

9.5

(9.5)

19.2

1.9

14.4

22.7

168

Disorders of continuity of bone

M84

1865

0.4

(0.4)

51.6

0.3

0.5

0.5

169

Other osteopathies

M86–M90

24,251

5.3

(5.3)

38.4

2.2

7.0

12.4

170

Other disorders of the musculoskeletal system and connective tissue

M95–M99

30,038

6.6

(6.6)

52.1

5.4

7.4

8.2

 

N—Diseases of the genitourinary system

N18

20,162

4.4

(4.5)

59.4

1.0

4.8

20.0

171

Chronic renal failure (CRF)c

N18

20,162

4.4

(4.5)

59.4

1.0

4.8

20.0

 

Q—Congenital malformations, deformations and chromosomal abnormalities

Q00–Q56; Q60–Q99

124,898

27.4

(27.5)

41.7

33.9

23.2

16.2

172

Congenital malformations: of the nervous, circulatory and respiratory systems, cleft palate and cleft lip, urinary tract, bones and muscles, other and chromosomal abnormalities not elsewhere classified

Q00–Q07; Q20–Q37; Q60–Q99

85,534

18.8

(18.9)

37.8

23.7

15.6

9.8

173

Congenital malformations of eye, ear, face and neck

Q10–Q18

19,689

4.3

(4.3)

38.8

6.2

3.0

1.8

174

Other congenital malformations of the digestive system

Q38–Q45

6481

1.4

(1.4)

41.8

1.0

1.6

2.9

175

Congenital malformations of the sexual organs

Q50–Q56

16,192

3.6

(3.6)

64.3

4.1

3.3

1.9

 

F—Mental and behavioural disorders

F00–99

683,194

150.0

(150.7)

41.0

135.2

150.2

223.7

176

Dementiac

F00, G30, F01, F02.0, F03.9, G31.8B, G31.8E, G31.9, G31.0B

36,803

8.1

(8.1)

36.3

0.0

3.7

71.7

177

Organic, including symptomatic, mental disorders

F04–F09

26,430

5.8

(5.9)

48.8

2.5

5.8

22.6

178

Mental and behavioural disorders due to use of alcohol

F10

59,143

13.0

(13.2)

67.0

9.4

17.5

7.9

179

Mental and behavioural disorders due to psychoactive substance use

F11–F19

53,669

11.8

(11.9)

54.2

13.3

11.2

7.2

180

Schizophreniac

F20

29,422

6.5

(6.5)

58.2

7.1

6.6

2.2

181

Schizotypal and delusional disorders

F21–F29

39,694

8.7

(8.8)

50.3

9.2

8.7

6.2

182

Bipolar affective disorderc

F30–F31

22,669

5.0

(5.0)

40.6

3.6

6.2

5.7

183

Depressionc

F32, F33, F34.1, F06.32

454,933

99.9

(100.2)

35.5

79.1

107.5

165.8

184

Mood (affective) disorders

F340, F348–F349, F38–F39

6887

1.5

(1.5)

35.9

1.3

1.6

1.7

185

Phobic anxiety disorders

F40

14,324

3.1

(3.2)

33.4

5.0

1.9

0.3

186

Other anxiety disorders

F41

38,079

8.4

(8.4)

32.6

10.0

7.3

5.3

187

Obsessive compulsive disorder (OCD)c

F42

10,062

2.2

(2.2)

36.7

3.8

1.0

0.5

188

Post-traumatic stress disorder

F431

16,055

3.5

(3.6)

48.6

3.9

3.8

0.4

189

Reactions to severe stress and adjustment disorders

F432–F439

61,701

13.5

(13.7)

39.1

18.6

10.4

4.4

190

Dissociative (conversion) disorders, somatoform disorders and other neurotic disorders

F44, F45, F48

21,420

4.7

(4.7)

31.7

4.6

5.2

3.1

191

Eating disorders

F50

7751

1.7

(1.7)

5.2

3.5

0.3

0.1

192

Behavioural syndromes associated with physiological disturbances and physical factors

F51–F59

6163

1.4

(1.3)

46.3

1.9

1.0

0.3

193

Emotionally unstable personality disorder

F603

21,848

4.8

(4.9)

21.2

7.7

2.8

0.2

194

Specific personality disorders

F602, F604–F609

50,415

11.1

(11.2)

39.3

14.4

9.4

2.7

195

Disorders of adult personality and behaviour

F61–F69

17,533

3.8

(3.9)

44.3

5.0

3.3

0.7

196

Mental retardation

F70–F79

13,822

3.0

(3.1)

53.9

3.8

2.6

1.2

197

Disorders of psychological development

F80–F89

9911

2.2

(2.2)

65.4

4.1

0.6

0.3

198

Hyperkinetic disorders (ADHD)c

F90

42,908

9.4

(9.5)

60.6

17.1

3.5

1.0

199

Behavioural and emotional disorders with onset usually occurring in childhood and adolescence

F91–F99

39,602

8.7

(8.8)

48.3

11.8

6.6

3.7

 

Having one or more chronic conditions

 

2,989,441

656.2

(657.2)

45.5

480.5

771.5

953.9

Standardised rates in brackets

See table with 10-year age intervals in Supplementary Material 2 in the electronic supplementary material

Conditions marked ‘A’, overlap with other conditions and are thus not counted twice [44]

ICD-10 International Statistical Classification of Diseases, 10th Revision

c Complex defined conditions; see reference for further details [44]

** 2-year prevalence

In general, prevalence naturally increases with increasing age across most conditions (see also Supplementary Material 2 and 6 with 10-year age intervals). Moreover, patients are relatively older within cancers and endocrine, nutritional and metabolic diseases and diseases of the circulatory system, the eye and adnexa, the ear and mastoid process, and the musculoskeletal system and connective tissue compared to within other conditions. A relatively younger patient population is seen within diseases of the respiratory system (especially allergies and asthma) and mental- and behavioural disorders. Mental disorders actually show a decrease in prevalence in later life. The conditions with the youngest population are, for example, seen within human immunodeficiency virus (HIV) and hepatitis.

Gender differences are seen across conditions, where women are overrepresented within most conditions—except, for example, heart failure and ischaemic heart diseases, stroke, some cancers, diabetes, disturbances in lipoprotein circulation and other lipids, inguinal hernia, hearing loss such as tinnitus, chronic renal failure, sleep disorders, schizophrenia, attention deficit/hyperactivity disorder (ADHD), mental and behavioural disorders due to the use of alcohol, and others. Coherently, women are treated more often than men with medication, except for ischaemic heart medications.

Some further characteristics and differences between conditions are seen and described in Supplementary Material 1–6. This includes geographic regional tables, further age characteristics with mean age and SD, more age intervals, further comments on common selected conditions and regional differences, etc.

4 Discussion

Based on the present findings, almost two-thirds of the entire Danish population aged 16 years or above have one or more chronic condition. Seen in the context of previous studies, this is around 10–20 percentage points higher than several other Danish studies [6, 7] as well as international studies [27, 28]. The overall estimates are also twice the official estimates of the Danish National Board of Health [8]. However, both national and international comparisons are difficult due to differences in methodology and data possibilities, so estimates should be compared with caution. For example, some American studies report that about 50% of the US population has a chronic condition [52, 53], but reliable overall estimates are difficult to obtain as to why improvement has been recommended [17]. Furthermore, as the US often has higher disease prevalence than the EU—often differing by 20–100% across different conditions [54] —the present study suggests that the US estimates might be even higher.

4.1 Strengths and Limitations

The strength of this study is the detailed, full nationwide register-based collection and categorisation of all data on actual chronic conditions and treatments for Danes in public and private healthcare. Several limitations exist, however, one being the obvious fact that being treated for a chronic condition is not necessarily the same as being truly ill. There may be cases of defensive medicine or patients being treated on suspicion of a chronic disease, or even wrong (over-) diagnosis.

As found in previous studies, one of the main limitations of register studies in general is the opposite, i.e. not being able to identify either chronic patients who have not been treated or diagnosed at any time or patients with self-treated conditions, who consequently are not reported in hospital or other registers (i.e. data source limitations, etc.) [44, 55]. This may lead to under-reporting of some less severe chronic conditions, such as asthma, allergies, COPD and type 2 diabetes, which are mostly treated in primary care where there is no reporting of diagnoses. The same might apply for other conditions such as glaucoma, cataracts, age-related hearing loss, other eye and ear conditions, and less severe mental conditions that are untreated, such as mild forms of depression or anxiety [44]. Thus, differences in the present study are compared with the national self-reported prevalence rates for 2013 for 18 broadly defined conditions where possible, since they cover a wide range of conditions of importance for assessment [6]. In comparison, differences and limitations of register-based definitions might be found within four of the 18 conditions: osteoarthritis, migraine/headache, tinnitus and cataracts. These conditions are discussed in more detail in Supplementary Material 3. All in all, these register-based less severe conditions may not be sufficiently estimated at this time, which is why register-based prevalence will be underestimated and should be used with caution.

While some estimated conditions show limitations compared to self-reported conditions, most other conditions, such as hypertension, rheumatoid arthritis, osteoporosis, diabetes, COPD, bronchitis and other lung diseases, cancers, heart condition and stroke, all have higher or slightly higher register-based than self-reported prevalence [6], as well as estimates in line with other studies [7, 10, 33, 55, 56]. The same applies to mental conditions overall, which typically have a lower survey response [57], which could explain the lower self-reported prevalence. Added to the fact that these estimates are free of self-reported bias, this clearly strengthens the reliability of most register-based conditions reported, not to mention the enhanced precision of doctor-reported diagnoses.

However, similar to non-registration issues in community-based surveys, misclassification issues also exist in register studies as sources of bias. Reasons for this include different coding practices between hospitals [30], different access to specialists, clinical disagreements, different clinical and administrative practices and interpretation of the ICD-10 criteria [58]. However, we do not have evidence of systemic misclassification. On the contrary, studies have validated reported diagnoses from registers for several psychiatric and somatic conditions, with good overall results [55, 59, 60, 61, 62, 63, 64]. Nevertheless, the estimates of some complex-aetiology, ill-defined and debated rheumatoid conditions such as fibromyalgia and chronic fatigue syndrome, even though common, should be used with caution since they are clearly under-reported compared to other studies [58, 65, 66]. Further discussion and references regarding the validity of diagnosis codes in registers can be found elsewhere [44].

In summary, the prevalence of some less severe conditions may be underestimated in register studies [55]. On the other hand, community-based self-reported studies may underestimate, especially, the more severe conditions due to, among other things, non-responders as well as people living in institutions or jails, homeless people, and those currently in inpatient treatment. Existing studies have already shown varying or poor overlap between self-reports and hospital reports [67], some concluding that the use of self-reports is less reliable in cases of, for example, stroke and ischaemic heart disease [68, 69], while severe conditions [67] such as cancers cannot reliably be self-diagnosed. Thus, a strength of the current study is that moderate or severe conditions are estimated more accurately and are naturally free of the bias of self-reported conditions. From this perspective, community-based survey studies contrast with and complement register studies [55].

Another strength of the study is that the definitions used were evaluated by epidemiologists and clinicians to strengthen reliability and provide the best possible representation [44]. In addition, the long register time periods are noticeable strengths compared to other register studies [7, 24, 26, 29, 30, 31]. Lastly, the use of a complete population of 4,555,439 people, not to mention the large number of ICD-10 doctor-reported conditions included, is another strength not or rarely seen in other studies.

4.2 Implications

Existing international register studies usually help determine current disease burden with implications for, for example, the funding of new treatments or others—but usually not multiple conditions [70, 71, 72].

The prevalence estimates of the current study provide unbiased, independent important basic information regarding the burden of disease for use in healthcare planning, as well as economic, aetiological and other research for a broad range of conditions. As it is based on uniform methodology within a single study, it also makes reliable comparisons, contrary to most existing studies. In many types of health economic studies, such as analyses of cost of illness and the budgetary consequences of the introduction of new health technologies, economic calculations may not provide an accurate, reliable picture if based on invalid information. This comprehensive catalogue of prevalence information of nationwide chronic conditions enables comprehensive comparisons of chronic diseases for policymakers, patient associations and researchers. Thus, it may serve as an off-the-shelf tool for decision makers and researchers for health economic modelling.

4.3 Future Studies

The World Health Organization (WHO) have recommended further improvement in data surveillance of chronic conditions worldwide [17]; in addition, other studies have criticised, as well as recommended, methodological improvements [73, 74, 75, 76]. Future studies should compare these prevalence rates based on actual patient pathways and registrations of treatment with other methods for estimating disease prevalence. Future studies could also focus on the development over time of disease burden, including the newest register data and analysis of possible trends in diagnosis or possible over-diagnosis. Moreover, while there are several studies exploring the coherence between self-reported conditions and hospital records, we found no studies assessing whether less severe self-reported conditions are more accurately estimated than register-reported conditions. Further studies should be carried out to assess whether chosen less severe self-reported conditions are estimated accurately, and if so, how register and self-reported study designs could best complement each other and for which conditions.

5 Conclusions

The current study provides a catalogue of prevalence for 199 different doctor-reported chronic conditions and groups of conditions by gender, based on a complete nationwide population sample.

To the best of the authors’ knowledge, this study provides the most comprehensive descriptive register study of the prevalence of treatment of chronic conditions. Hence, the overall prevalence rate found is higher than that found in several previous studies, indicating that almost two-thirds of the entire Danish population aged 16 years or above either have a hospital diagnosis and/or are in medical treatment for one or more chronic condition.

Notes

Acknowledgements

Special thanks to data management specialists Ole Schou Rasmussen and Thomas Mulvad Larsen from the North Denmark Region, and Niels Bohrs Vej, 9220 Aalborg OE, Denmark, for very useful and helpful suggestions and assistance in data management and SAS programming of the definitions, which has been much appreciated.

Author Contributions

All authors contributed to the study design. MFH did all data collection and programming and drafted the manuscript. All authors discussed and interpreted empirical findings. Critical manuscript revision and final approval of the manuscript was done by all authors.

Compliance with Ethical Standards

Funding

The project was supported financially by the North Denmark Region, the Tax Foundation (public) and Aalborg University.

Conflict of interest

Michael Falk Hvidberg: None declared. Soeren Paaske Johnsen: None declared. Michael Davidsen: None declared. Lars Ehlers: None declared.

Supplementary material

41669_2019_167_MOESM1_ESM.pdf (2.2 mb)
Supplementary material 1 (PDF 2267 kb)

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Authors and Affiliations

  • Michael Falk Hvidberg
    • 1
    Email author
  • Soeren Paaske Johnsen
    • 2
  • Michael Davidsen
    • 3
  • Lars Ehlers
    • 1
  1. 1.Danish Center for Healthcare ImprovementsAalborg UniversityAalborgDenmark
  2. 2.Department of Clinical EpidemiologyAarhus University HospitalAarhus NDenmark
  3. 3.National Institute of Public HealthUniversity of Southern DenmarkCopenhagen KDenmark

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