An evaluation of laboratory tests for the detection and differential diagnosis of Cushing's syndrome

1. Results of tests for the diagnosis of Cushings syndrome of varoius aetiologies are discussed for twenty-five patients in whom the pathology was established by operation or autopsy. 2. Control values for the urinary excretion of free cortisol, 17-OHCS, Porter-Silber chromogens (P-SC) and 17-OS and plasma levels of P-SC are compared with those for normal subjects. 3. The results indicated that urinary values are within the normal range for some patients with Cushing's syndrome. 4. Plasma levels of P-SC in the morning were within the normal range for the majority and elevated for the rest. 5. Some patients showed day-night variation of plasma P-SC but evening values were above the normal range. 6. The expected response for low dosage dexamethasone was found in all patients tested but unexpected responses followed high dosage in some. 7. Plasma 11-OHCS in the five patients tested failed to respond to insulin induced hypoglycaemia. 8. Metyrapone administration and corticotrophin infusion tests had limited usefulness in establishing the aetiology of the disease. The 17-OHCS excretion became raised in the response to corticotrophin and the evaluation was prolonged beyond normal responsiveness.