Pediatric Reference Intervals for Thyroid-Stimulating Hormone, Free Thyroxine, and Free Triiodothyronine Assayed on a Roche Cobas Immunoassay Analyzer

Çağrı Umut, Fatma Ceyla Eraldemir, Tuncay Müge Alvur, Sibel Balci

Keywords: TSH; freeT4; freeT3; Roche cobas 8000; Thyroid hormones; Reference Intervals

Aim:

Reliable and accurate reference intervals (RIs) are crucial for the proper interpretation of clinical laboratory test results. With this study, we aimed to establish pediatric RIs for thyroid-stimulating hormone (TSH), free thyroxine (fT4), and free triiodothyronine (fT3) based on age and gender in our laboratory.

Method:

Between May 1, 2021, and November 30, 2022, measurements of TSH, fT4, and fT3 from patients under 18 years of age were retrieved from the laboratory information system (LIS). Patients from departments with a high likelihood of pathological results, such as intensive care, endocrinology, infectious diseases, oncology, and hematology, as well as those with positive Thyroglobulin antibody (Anti-TG) and Thyroid peroxidase antibody (Anti-TPO) results, were excluded from the study. All analyses were conducted using the electrochemiluminescence method on the Roche Cobas 8000 e 801 analyzer. Parametric and nonparametric methods, outlier detection, and age stratification were used to establish the RIs. Statistical analyses were conducted using statistical package programs.

Results:

As a result of statistical analyses, separate age groups were established for each gender. These groups included three categories for the first year of life (0-15 days, 16-30 days, and 2-12 months), as well as individual age groups from 1 year to 18 years (resulting in 21 groups). Our findings demonstrate that reference values for fT4 and fT3 in children gradually decrease with advancing age, approaching values observed in adults, which is consistent with the literature. TSH levels exhibited a decreasing trend with age.

Conclusions:

Establishing age-specific RI is critical, particularly in newborns, where physiological TSH levels are elevated, to prevent misdiagnosis believe. When using pediatric RIs tailored to our population in patient result reports, we anticipate that it will offer a more dependable foundation for diagnosing evolving endocrine changes in childhood and adolescence. This, in turn, can improve diagnostic precision and treatment effectiveness in pediatric thyroid disorders.

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