Clinical significance of mildly elevated thyrotropin levels with normal thyroxine levels

The meaning of minor elevations in the thyrotropin level (less than 10 mIU/ml) in association with a normal thyroxine level has been questioned. Although such findings are presumed to be indicative of subclinical hypothyroidism, consideration of other causes can pose problems with diagnosis. We investigated the clinical significance of equivocal elevation of thyrotropin values with a normal thyroxine level and free thyroxine index in 31 patients evaluated with a thyrotropin releasing hormone (TRH) stimulation test and antithyroid antibody determinations. Patients were categorized as euthyroid or hypothyroid on the basis of TRH responsiveness. Of the 31 patients, 23 (74%) were hypothyroid, resulting in a positive predictive value as high as 81%. Eight of 21 hypothyroid patients (38%) had antimicrosomal antibodies, and only one euthyroid patient had antimicrosomal antibodies. We find that equivocally elevated thyrotropin values indicate primary hypothyroidism about 80% of the time. The combination of a mildly elevated thyrotropin level and antimicrosomal antibodies is seen almost exclusively in patients with thyroid failure.