COMPARISON OF TESTS OF STRESS-RELEASED CORTISOL SECRETION IN PITUITARY DISEASE

OBJECTIVES We wished to compare peak and incremental rise in plasma co rtisol in response to insulin induced hypoglycaemia (IIH) stress test, i.m. glucagon stimulation test (IMGST) and short Synacthen test (SST) in patients with pituitary disease, using a modern radioimmunoassay f or cortisol. We compared the three stimulants using receiver operator characteristic (ROC) plots, assuming a cortisol threshold of 500 nmol/ l or 580 nmol/l for the IIH stress test which we used as the standard from which to evaluate the SST and the IMGST. PATIENTS AND DESIGN We p rospectively studied 16 patients (8F, 8M mean age 43.69 +/- 3.72 years ) admitted to the investigation ward for IIH stress test and who were asked to undergo two additional tests (IMGST and SST) on consecutive d ays. MEASUREMENTS We measured serum cortisol at baseline, 30, 45, 60, 90 and 120 minutes during the IIH stress test; baseline, 150 and 180 m inutes during GST, and baseline and 30 minutes during the SST. RESULTS There was a significant rise in cortisol from baseline in all tests ( P < 0.001). There was no significant difference among the peak plasma cortisol responses or the incremental rises in plasma cortisol followi ng IMGST, SST and IIH stress test (repeated measures ANOVA F = 0.704, P = 0.503; F = 0.238, P = 0.79). The ROC plots clearly showed that the SST has poor diagnostic utility at both IIH thresholds, compared with the IMGST. CONCLUSION The peaks and incremental rises in cortisol fol lowing all three tests are comparable. Using the insulin induced hypog lycaemia stress test as a reference and peak cortisol thresholds of 50 0 and 580 nmol/l as discriminating variables, the short Synacthen disp layed poor diagnostic utility when compared to the i.m. glucagon stimu lation test. The short Synacthen may be misleading if used as a screen ing test as advocated by a number of authors.