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.

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Background: The aim of this study was to determine the reference intervals (RIs) for thyroid stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3) and FT3/FT4 ratio using indirect methods. Methods: We analysed 1256 results TSH, FT4 and FT3 collected from a laboratory information system between 2017 and 2021. All measurements were performed on a Siemens ADVIA Centaur XP analyser using the chemiluminescent immunoassay. We calculated the values of the 2.5th and 97.5th percentiles as recommended by the IFCC (CLSI C28-A3). Results: The RIs derived for TSH, FT4, FT3 and FT3/FT4 ratio were 0.34-4.10 mIU/L, 11.3-20.6 pmol/L, 3.5-6.32 pmol/L and 0.21-0.47, respectively. We found a significant difference between calculated RIs for the TSH and FT4 and those recommended by the manufacturer. Also, FT3 values were significantly higher in the group younger than 30 years relative to the fourth decade (5.26 vs. 5.02, p=0.005), the fifth decade (5.26 vs. 4.94, p=0.001), the sixth decade (5.26 vs. 4.87, p˂0.001), the seventh decade (5.26 vs. 4.79, p˂0.001) and the group older than 70 years old (5.26 vs. 4.55, p˂0.001). Likewise, we found for TSH values and FT3 / FT4 ratio a significant difference (p <0.001) between different age groups. Conclusions: The establishing RIs for the population of the Republic of Srpska were significantly differed from the recommended RIs by the manufacturer for TSH and FT4. Our results encourage other laboratories to develop their own RIs for thyroid parameters by applying CLSI recommendations.