TSH level is very important to determine the function of thyroid gland.
The normal range has been changed racently to more accurate figures.
I chose this article for refreshing of knowledge to the thyroid treating doctors.


New Criteria for Diagnosis and Management


By Stephanie L. Lee, MD


Recommendation for a new normal TSH reference range.

The TSH reference range of 0.4 to 4.0 mIU/L is considered normal based on the results of general cross-sectional population studies lacking well-defined reference populations.1 In contrast, the third National Health and Nutrition Examination Survey (NHANES III) screened 17 353 subjects and excluded those with a history of thyroid disease, goiter, pregnancy, or biochemical hypo- or hyperthyroidism, and those taking thyroid medication, androgens or estrogens.2 In the resulting “normal” reference population of 13 344 subjects, 95% had TSH levels that fell between 0.3 and 2.5 mIU/L . Though TSH levels increased slightly with age, the highest mean TSH level of the normal population was slightly higher than 2 mIU/L, and the average level across all ages was only 1.49 mIU/L (Figure 2). These data were consistent with those of the smaller Andersen study, in which TSH levels measured in 16 normal men fell between 0.16 and 2.4 mIU/L with a mean of 1.27 mIU/L .Taken together, these findings support the establishment of a new normal reference TSH range from 0.5 to 2.5 mIU/L, with subclinical
hypothyroidism defined as a TSH level between 2.5 and 10 mIU/L with a normal free thyroxine (FT4) level, and overt hypothyroidism as TSH greater than 10 mIU/L with a suppressed FT4 level.


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