Indirect Estimation of the Pediatric Reference Intervals for Thyroid Function Tests in Public Health Laboratory

Reference intervals (RI) are an essential section of the information that medical laboratories present to clinicians to facilitate the management process of the patient. Thyroid-stimulating hormone (TSH), free thyroxine (fT4), and free triiodothyronine (fT3) are the most valuable and cost-effective parameters of thyroid functions. According to the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), Clinical and Laboratory Standards Institute (CLSI), and American Thyroid Association (ATA), every laboratory should determine own RI on own population and method. In this study we aim to evaluate the pediatric reference intervals in a public health laboratory.

The results of TSH, fT4, and fT3 from pediatric patients (aged: 0 - 18 years) were included in our study. These results were stored in our laboratory information system. TSH, fT4, and fT3 are measured in Abbott Architect i2000 (Abbott Diagnostics, Abbott Park, IL, USA) chemiluminescent microparticle immunoassay analyzer. RI study was conducted according to CLSI EP28-A3 guidelines. Results were evaluated with MedCalc ver. 19.2.1 (MedCalc Software Ltd., Ostend, Belgium), and Minitab 19.2 (Minitab Statistical Software, AppOnFly Inc., San Fransisco, CA, USA).

The final study included 483 samples. Study sample consisted of 288 girls and 195 boys. Our reference intervals for TSH, fT4 and fT3 were found as 0.74 - 4.11 mIU/L, 0.80 - 1.42 ng/dL, and 2.40 - 4.38 pg/mL, respectively. Reference intervals were compatible with expected values in the insert sheets, except for fT3.

Laboratories should implement their reference intervals based on CLSI C28-A3 guidelines.