Direct Estimation of Reference Intervals for Thyroid Parameters in the Republic of Srpska

Abstract

summaryBackgroundThe aim of this study was to determine the reference values for thyrotropin (TSH), thyroid hormones (total and free thyroxine, T4 and fT4; total and free triiodothyronine, T3 and fT3), thyroglobulin (Tg) and thyroid antibodies (thyroid peroxidase, TPOAb and thyroglobulin antibody, TgAb) in the population of the Republic of Srpska.MethodsA total of 250 euthyroid subjects were enrolled in this study. A direct method for choosing reference subjects was used to establish reference intervals. The hormones and thyroid antibodies were measured by an electrochemiluminescence immunoassay method (ECLIA, Roche Diagnostics, Mannheim, Germany). We calculated the reference intervals by MedCalc, version 12.1.4.0 (MedCalc software, Belgium) as recommended by the IFCC (CLSI C28-A3).ResultsUsing guidelines recommended by the National Academy of Clinical Biochemistry (NACB) and based on standard statistical approaches, the reference intervals derived for TSH, fT4, T4, fT3, T3 were 0.75–5.32 mIU/L, 12.29–20.03 pmol/L, 73.49–126,30 nmol/L, 4.11–6.32 pmol/L, 1.15–2.32 nmol/L and for Tg, TPOAb, TgAb were 3.63–26.00 μg/L, <18.02 mIU/L, < 98.00 mIU/L, respectively. We found a significant difference (p<0.05) in TSH and fT3 values between different age groups as well as in T4, fT4 and fT3 values between ge nder groups.ConclusionsThe established reference values for the population of the Republic of Srpska were significantly different from the values recommended by the manufacturer of reagents (Roche Diagnostics). Our results showed that a laboratory needs to establish its own reference values in order to set up a proper diagnosis, as well as to treat patients successfully.

Age and Assay Related Changes of Laboratory Thyroid Function Tests in the Reference Female Population

“…Different data suggest that the change in thyrotropin levels with age varies depending on the iodine status of the population. The results of our investigation are consistent with some other previously conducted large population studies in areas with adequate iodine supplementation (6, 22, 24), showing that the median, lower and upper reference limits of the serum thyrotropin values of female subjects continuously increased with age. Data from NHANES III show an increase in the hormone values with age in subjects with no biochemical or clinical signs of thyroid disease (28).…”

“…The determination of its reference limits (especially the upper limit) is challenging for many different reasons and has been a subject of ongoing debate for the last fifteen years. Median population thyrotropin values are usually between 1–1.5 mU/L (5, 6) but they do not have a normal distribution, and rather display a right skewed one, with a long tail towards higher values. In 2005, Wartofsky and Dickey (7) advocated the lowering of the upper TSH limit from 4–5 mU/L to 2.5 mU/L since more than 95% of the normal population has a value below this limit.…”

Gender- and age-specific reference intervals of common biochemical analytes in chinese population – derivation using real laboratory data

“…It is necessary to establish RIs for common analytes at large three-level general hospitals because the concentration of a given analyte may be affected by various factors such as gender, age, and ethnicity, among others (3). Numerous studies have reported common RIs based on traceable results that can be used for analytes with good traceability from different manufacturers to the same higher-order references (4)(5)(6). Reliable RIs are determined in completely healthy individuals but show variations (7)(8)(9)(10).…”

Use of the Free Thyroxine Index to Refine the Lower Limit of a Free Thyroxine Immunoassay for Detection of Secondary Hypothyroidism

“…immunoassays frequently underestimate FT4 concentrations, possibly due to T4 sequestration by assay materials (9). Finally, reference ranges for a particular local population may differ from the manufacturer's documentation (10). The Clinical Laboratory Improvement Amendments of 1988 stipulate that manufacturers' reference intervals must be validated for a laboratory's patient population (11), though in practice, the necessary internal testing to verify the reference range is frequently not performed (12).…”