This US-based, retrospective, observational study used healthcare claims data from the Truven Health MarketScan Commercial Claims and Encounters (Commercial) database and the MarketScan® Medicare Supplemental (Medicare) database. These databases include complete longitudinal records of inpatient services, outpatient services, long-term care, and prescription drug claims for commercially insured and Medicare-eligible patients covered under a variety of health plans. All study data were de-identified and compliant with protocols of US patient confidentiality requirements, including the Health Insurance Portability and Accountability Act of 1996. Because this study used only de-identified patient records and did not involve the collection, use, or transmittal of individually identifiable data, institutional review board approval to conduct this study was not necessary.
This study included patients aged ≥ 18 years with ≥ 1 inpatient or ≥ 2 non-rule-out outpatient medical claims for AS [International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis code 720.0] > 30 days but ≤ 365 days apart between January 1, 2012, and December 31, 2014. Patients with AS were required to have ≥ 1 diagnosis code for AS during 2013; the year 2013 was chosen because of the availability of pharmacy and medical claims data at the time of the analysis. The index date was defined as the date of the first AS diagnosis claim. Diagnoses on claims for diagnostic or rule-out procedures (e.g., laboratory, pathology, radiology services) were excluded.
Continuous enrollment with medical and pharmacy benefits for at least 12 months before the index date (baseline period) and 12 months after the index date (follow-up period) was required. Patients without AS (general population) were required to have no diagnosis of AS anytime between January 1, 2007, and June 30, 2015. These control patients were matched to patients with AS at a ratio of up to 5:1 by age, geographic location, index calendar year, and sex. Matched controls were assigned the same index dates as their matched patients with AS. All patients were followed up for at least 12 months until the earliest occurrence of inpatient death, the end of continuous enrollment, or the end of data availability (June 30, 2015). The 12-month follow-up period was chosen in order to present the data over a fixed 12-month period for clarity and ease of understanding.
Patient demographic characteristics were recorded at the index date and included age, geographic area, insurance type, and sex. Comorbidities of interest were identified using ICD-9-CM codes in a medical claim; however, claims for diagnostic or rule-out procedures such as laboratory, pathology, or radiology services were excluded to avoid incorrectly identifying patients as having a comorbidity based on the testing rather than the test results. The following comorbidities were recorded during the baseline and follow-up periods: cardiovascular conditions (angina, atherosclerosis, cerebrovascular disease/stroke, coronary artery disease, hypertension, myocardial infarction, peripheral vascular disease, venous thromboembolism), inflammatory bowel disease (Crohn’s disease, ulcerative colitis), gastrointestinal ulcers (esophageal, gastric, duodenal, peptic, gastrojejunal ulcers), malignant neoplasms (malignant solid tumors, hematologic malignancies, neuroendocrine tumors), asthma, depression, diabetes mellitus, dyslipidemia, multiple sclerosis, osteoporosis, Parkinson disease, psoriasis, sleep apnea, spinal fracture, and uveitis.
All-cause and AS-specific healthcare utilization and associated direct costs were recorded during the follow-up period and reported as per patient per year. The following categories of healthcare utilization were reported: presence and number of inpatient hospitalizations; emergency department (ED) visits, nonhospital-based outpatient visits, hospital-based outpatient visits (includes the same type of visits as nonhospital-based outpatient visits but in a medical office within a hospital), and other outpatient services (e.g., skilled nursing facility, home health services, physical therapy, laboratory tests, imaging, outpatient procedures, injections); outpatient pharmacy claims; and counts of unique medications at the therapeutic class level including nonsteroidal anti-inflammatory drugs (NSAIDs), corticosteroids, conventional synthetic disease-modifying antirheumatic drugs (csDMARDs), TNFis approved for the treatment of AS by the FDA, and comorbidity-specific medications (e.g., antidiabetic, antihypertensive, lipid-lowering, and antidepressant therapies).
Costs were the total reimbursed amount, including patients’ copays, deductible, and coinsurance. All costs were inflated to 2015 dollars, using the medical component of the Consumer Price Index. The following categories of direct healthcare costs were reported: total healthcare costs, inpatient, outpatient (ED, nonhospital-based outpatient, hospital-based outpatient, and other outpatient services), and total outpatient pharmacy costs [included National Drug Code (NDC) claims only]. AS-specific healthcare resource utilization and associated costs were defined as inpatient or outpatient (ED, nonhospital-based outpatient, hospital-based outpatient, and other outpatient services) claims with the diagnosis code for AS (ICD-9-CM 720.0) and AS medications (included NDC and the Healthcare Common Procedure Coding System claims). The outpatient diagnosis could be in any position, but the inpatient diagnosis was required to be a primary discharge diagnosis, and the whole hospitalization stay was considered AS specific.
Bivariate descriptive analyses were conducted on all study variables comparing patients with and without AS. Categorical variables were presented as counts and percentages, and mean (SD) and median [interquartile range (IQR)] healthcare utilizations and direct costs were reported. The statistical significance of cohort differences in bivariate descriptive statistics used χ2 tests for categorical variables, and t tests were used for differences in continuous variables. The threshold for statistical significance was set a priori to a P value of 0.05. All analyses were conducted using SAS version 9.4 (SAS Institute Inc.).