Methodological issues in the measurement of serum TSH--implications for psychiatry

The TSH response to TRH has been reported to be blunted in endogenous depression. We compared two radioimmunoassay (RIA) techniques of TSH in 21 subjects (7 psychiatric inpatients, 14 normal controls) to determine whether differences in assay could account for discrepancies in the reported prevalence rates of blunted TSH responses in depression. A highly significant correlation (p less than 0.001) was found between the delta MAX TASH values of the two assays. The mean delta MAX TSH of one assay was significantly greater than the mean of the second assay. One assay yielded 6 blunted TSH responses to TRH, while the other yielded 9 such responses. Different TSH assay methods might account for discrepancies of the prevalence rates of blunted TSH response in depression.