Thyrotropin reference range - should it be changed?

Abstract

Current thyrotropin (TSH) reference range established by sensitive assays is from 0.2-0.4 mj.m./l to 4.0-4.5 mj.m./l. Serum TSH reference range was performed using specimens from healthy volunteers without history of thyroid disease but the values distribution is not concordant with Gaussian curve and is skewed toward upper values. It is claimed that upper reference limit for TSH should be declained because of possible incorporation of individuals with unrecognized chronic lymphocytic thyroiditis into initial study. American National Academy of Clinical Biochemistry recommends to examine only euthyroid healthy volunteers without personal or family history of thyroid dysfunction, visible or palpable goiter, with no detectable thyroid antibodies measured by sensitive immunoassays and without any medication except estrogen. Many authors observed that even in such rigorously selected population the upper limit of TSH does not decrease significantly. The other possible factors which may influence TSH values are ethnic features, age, iodine intake, time of phlebotomy or assay sensitivity and specificity. Furthermore there are no epidemiological data showing adverse consequences of serum TSH between 3.0 mj.m./l and 5.0 mj.m./l. And because of it current upper limit for TSH should remain unchanged. However one must realize that many people with TSH values between 3.0 mj.m./l and 5.0 mj.m./l have unrecognized chronic lymphocytic thyroiditis and should be followed because of possible future hypothyroidism. The special care is needed for pregnant women or those planning to be pregnant.
(Pol J Endocrinol 2007; 58 (5): 454-460)