Alterations in thyroid function tests in major depression.

Most clinically euthyroid patients with acute or chronic nonthyroid illness have abnormal thyroid function which is called the euthyroid sick syndrome. To assess the euthyroid sick syndrome in depression, we examined levels of total thyroxine (TT4), total triiodothyronine (TT3), T3 uptake (T3U) by radio-immunoassay and thyrotropin (TSH) by immunoradiometric assay in a group of 46 patients with major depression (diagnosed according to DSM-III), 44 normal control subjects and 39 schizophrenics. As compared with the normal controls and schizophrenics, depressed patients showed the following significant differences: a reduction of the mean TT3 level by 26% (89.6 +/- 26.9 ng/dl versus 121 +/- 21.4 ng/dl, p less than 0.05), an increase in the mean T3U level by 6% (35.4 +/- 4.1 versus 33.1 +/- 3.0%, p less than 0.05), and a rise in the mean FT4I level by 15% (2.96 +/- 0.59 versus 2.50 +/- 0.40, p less than 0.05). However, both the mean TSH and TT4 levels in depressed patients were not significantly different from those in normal subjects and schizophrenics, though there was a trend toward high mean TT4 levels in depressed patients. Among the 46 depressed patients who had normal basal TSH levels, 7(15%), 3(6%) and 11 (23%) had the low T3 syndrome, low T3 plus low T4 syndrome and high T4 syndrome, respectively. The clinical implication of the low T3 or/and T4 low syndrome was discussed. All the abnormal thyroid indices in the 21 depressed patients were normalized after recovery of depression. These findings suggest that the euthyroid sick syndrome in depression might be a state-dependent phenomenon.