The influence of blood chemistry on T4 and FT4I in major depression.

The pathophysiology underlying thyroid dysfunction in some depressed patients has not yet been determined. In order to clarify possible biochemical influences on thyroid regulation in these patients, we retrospectively examined several thyroid indices in charts from 81 depressed inpatients and 82 psychiatric controls. The depressed group had significantly higher T4 levels and free T4 index (FT4I), as well as lower chloride (CL) levels than controls. Albumin (ALB) also tended to be higher in the depressives. After adjustment for previously reported effects of ALB and CL on thyroid hormone binding in plasma, the initial differences in thyroid indices became non-significant. We suggest from these findings that plasma biochemical factors contribute significantly to the transient changes in thyroid function observed in some acutely depressed patients. Potential explanations for these biochemical alterations are discussed.