Pre-analytical Factors Influence Accuracy of Urine Spot Iodine Assessment in Epidemiological Surveys
Urinary iodine concentration (UIC) is commonly used to assess iodine status of subjects in epidemiological surveys. As pre-analytical factors are an important source of measurement error and studies about this phase are scarce, our objective was to assess the influence of urine sampling conditions on UIC, i.e., whether the child ate breakfast or not, urine void rank of the day, and time span between last meal and urine collection. A nationwide, two-stage, stratified, cross-sectional study including 1560 children (6–12 years) was performed in 2012. UIC was determined by the Sandell-Kolthoff method. Pre-analytical factors were assessed from children’s mothers by using a questionnaire. Association between iodine status and pre-analytical factors were adjusted for one another and socio-economic characteristics by multivariate linear and multinomial regression models (RPR: relative prevalence ratios). Skipping breakfast prior to morning urine sampling decreased UIC by 40 to 50 μg/L and the proportion of UIC < 100 μg/L was higher among children having those skipped breakfast (RPR = 3.2[1.0–10.4]). In unadjusted analyses, UIC was less among children sampled more than 5 h from their last meal. UIC decreased with rank of urine void (e.g., first vs. second, P < 0.001); also, the proportion of UIC < 100 μg/L was greater among 4th rank samples (vs. second RPR = 2.1[1.1–4.0]). Subjects’ breakfast status and urine void rank should be accounted for when assessing iodine status. Providing recommendations to standardize pre-analytical factors is a key step toward improving accuracy and comparability of survey results for assessing iodine status from spot urine samples. These recommendations have to be evaluated by future research.
KeywordsUrinary iodine Pre-analytical step Epidemiological survey Iodine deficiency Breakfast Urine void rank
The work was supported by the Tunisian National Institute of Nutrition and Food Technology of the Tunisian Ministry of Health and by grants from the United Nations Children’s Fund (UNICEF) Tunisia.
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflicts of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Written informed consent was obtained from all individual participants included in the study.
- 2.Rothman KJ, Greenland S, Lash TL (2008) Modern epidemiology, 3rd edn. Lippincott Williams & Wilkins, PhiladelphiaGoogle Scholar
- 4.Kanagasabapathy A, Kumari S (2000) Guidelines on standard operating procedures for clinical chemistry. World Health Organization, GenevaGoogle Scholar
- 6.Aliasgharpour M (2016) The pre analytical phase: precautions in specimen collection and patient preparation for trace and ultra trace elements analysis. Int J Med Investig 5:139–145Google Scholar
- 7.Collery P, Bratter P, De Bratter VN et al (1998) Ions Métalliques en Biologie Et en Médecine: Cinquième Symposium International Sur Les Ions Métalliques en Biologie Et en Médecine (8–10 Mai 1998). John Libbey Eurotext, Neuherberg-Munich, AllemagneGoogle Scholar
- 8.Burtis CA, Ashwood ER, Bruns DE (2012) Tietz textbook of clinical chemistry and molecular diagnostics, 5th edn. Elsevier Health Sciences, MissouriGoogle Scholar
- 9.International Council for Control of Iodine Deficiency Disorders, United Nations Children's Fund & World Health Horganization (2007) Assessment of iodine deficiency disorders and monitoring their elimination: a guide for programme managers, 3rd edn. World Health Organization, GenevaGoogle Scholar
- 16.Doggui R, El Ati-Hellal M, Traissac P et al (2017) Adequacy assessment of a universal salt iodization program two decades after its implementation: a national cross-sectional study of iodine status among school-age children in Tunisia. Nutrients 9 9:6. https://doi.org/10.3390/nu9010006 CrossRefGoogle Scholar
- 18.Zimmermann MB, Aeberli I, Andersson M, Assey V, Yorg JAJ, Jooste P, Jukić T, Kartono D, Kusić Z, Pretell E, San Luis TOL Jr, Untoro J, Timmer A (2013) Thyroglobulin is a sensitive measure of both deficient and excess iodine intakes in children and indicates no adverse effects on thyroid function in the UIC range of 100-299 mug/L: a UNICEF/ICCIDD study group report. J Clin Endocrinol Metab 98:1271–1280. https://doi.org/10.1210/jc.2012-3952 CrossRefPubMedGoogle Scholar
- 21.Christiansen TB, Lauritsen JM (2008) EpiData data entry, data management and basic statistical analysis system. The EpiData Association, OdenseGoogle Scholar
- 22.StataCorp (2015) Stata statistical software: release. College Station, StataCorp LP, TX, p 14Google Scholar
- 24.Preedy VR, Burrow GN, Watson RR (2009) Comprehensive handbook of iodine: nutritional, biochemical, pathological and therapeutic aspects. Elsevier Science, BurlingtonGoogle Scholar
- 30.Perrine CG, Cogswell ME, Swanson CA, Sullivan KM, Chen TC, Carriquiry AL, Dodd KW, Caldwell KL, Wang CY (2014) Comparison of population iodine estimates from 24-hour urine and timed-spot urine samples. Thyroid 24:748–757. https://doi.org/10.1089/thy.2013.0404 CrossRefPubMedPubMedCentralGoogle Scholar
- 31.Wang CY, Cogswell ME, Loria CM, Chen TC, Pfeiffer CM, Swanson CA, Caldwell KL, Perrine CG, Carriquiry AL, Liu K, Sempos CT, Gillespie CD, Burt VL (2013) Urinary excretion of sodium, potassium, and chloride, but not iodine, varies by timing of collection in a 24-hour calibration study. J Nutr 143:1276–1282. https://doi.org/10.3945/jn.113.175927 CrossRefPubMedGoogle Scholar