TSH Responsiveness to TRH (“The TRH Test”) - of No Diagnostic Value in Depression

Serum free T4, free T3 and TSH (IRMA), along with TSH responsiveness to TRH (500 μg i.v.), were investigated in 12 patients, initially when severely depressed and again upon recovery, and in a group of age-matched controls. The TSH response to TRH did not differ significantly between patients and controls, nor did it alter with treatment of depression. There were no significant differences in basal TSH levels. Free T3 levels were very significantly lower in untreated patients than in controls (p = 0·004), as were free T4 levels (p = 0·02), and had not improved significantly at recovery. Basal TSH levels showed a strong association with the integrated TSH response to TRH (p < 0·001) in both patients and controls. Thus in depression, as in thyoid dysfunction, the TRH test can be abandoned in favour of sensitive basal TSH measurement but, more importantly, the TRH test has no value in the diagnosis of endogenous depression or in monitoring treatment response. However, there is a reduction in free thyroid hormone levels in depression which has not been rectified by the time of clinical recovery.