Serial dexamethasone suppression tests in psychiatric illness: Part III. The influence of intervening variables.

The effects of different intervening variables on dexamethasone suppression test (DST) results were evaluated in depressed, schizophrenic, and manic patients. There was a significant correlation between age and DST results in major depression. Some "isolated peaks" of DST nonsuppression were explained by low dexamethasone serum levels. In schizophrenic and manic patients, the dexamethasone concentrations increased to above the normal range during the study period. A significant negative correlation between dexamethasone concentrations and DST results was found in schizophrenia and mania, but not in depression. Dexamethasone levels were generally higher in men than in women. Weight loss and hospital admission affected the DST in individual cases, whereas length of episode and drug withdrawal did not. Thus, the intervening variables accounted for some of the abnormal DST results, but other factors such as severity of illness, nonspecific stress, or possibly depression itself emerged as the main causes of abnormal DST results.