New Reference Intervals for Thyrotropin and Thyroid Hormones Based on National Academy of Clinical Biochemistry Criteria and Regular

Background: The aim of our present study was to establish new reference intervals for thyrotropin (TSH) and thyroid hormones based on National Academy of Clinical Biochemistry (NACB) criteria and regular thy-roid ultrasonography. We also assessed the effect of potentially confounding factors to modulate the limits of these intervals. Methods: We investigated 870 apparently healthy per-sons and excluded, step by step, those with a family history of thyroid disease, pathologic thyroid ultra-sonography results, and increased anti-thyroid peroxi-dase or anti-thyroglobulin antibodies. Accordingly, only 453 of the 870 persons in the entire group were finally included as reference collective. We measured serum concentrations of TSH, total and free thyroxin