Abstract:

The purpose is to determine the reference intervals of the thyroid-stimulating hormone (TSH), free T4 (sT4) and free T3 (sT3) tests by indirect method from our laboratory results data and to compare the reference intervals with the reference intervals recommended by the kit and method manufacturer we use. Tools and Methods: TSH, sT4 and sT3 results of 195205 people between the ages of 1 and 99 who were studied in our laboratory between January and October 2021 were included in the study. The Tukey method was used for determining and excluding end values. Then the reference intervals of TSH, sT4 and sT3 were calculated with non-parametric and Bhattacharya methods. In the assessment of the compatibility between reference intervals, CLIA 19 used acceptable limits. Results: Reference intervals for the pediatric age group (1-17 years) were found as TSH (0,56 - 5,93 mIU/L), sT4 (8,9 - 16,1 ng/L) and sT3 (2,74 - 5,39 ng/L) with non-parametric method; with Bhattacharya method, TSH (0,67 - 3,08 mIU/L), sT4 (9,2 - 16,1 ng/L) and sT3 (2,72 - 5,46 ng/L) were found. Reference intervals for the adult age group (18-99 years old) were found as TSH (0,10 - 4,98 mIU/L), sT4 (8,7 - 16,1 ng/L) and sT3 (2,01 - 4,09 ng/L) with non-parametric method; with Bhattacharya method TSH (0,18 - 3,07 mIU/L), sT4 (9,1 - 16,2 ng/L) and sT3 (2,05 - 4,13 ng/L). The result is that our sT4 and sT3 reference intervals can be accepted as compatible with the reference intervals of the manufacturer but we have determined the difference between the upper reference limit in the pediatric group and the lower reference limit in the adult group and the reference limit of the manufacturer for the TSH test. We consider that the laboratory’s determination of its own reference intervals is of great importance for the proper interpretation of the test results.

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