OBJECTIVE
To assess the integrity of the hypothalamo-pituitary-adrenal(HPA) axis, many authors have proposed the short synacthen test (ACTH1-24, Tetracosactrin) as a replacement for the insulin tolerance test (ITT). The aim of this study was to compare the plasma cortisol response obtained with both short synacthen tests (high dose (HDT, 250 microgram) and low dose (LDT, 1 microgram)) with the peak reached during the ITT in healthy volunteers, and to establish the plasma cortisol cut-off level in each test.
SUBJECTS AND METHODS
Thirty healthy subjects (16 F, 14 M), mean age 34 years, underwent both short synacthen tests. Twenty healthy subjects, 15 of whom (11 F, nine M) belonged to the above group, mean age 30 years, underwent an ITT. Plasma cortisol was measured using a chemiluminiscence immunoassay.
RESULTS
There were no differences between plasma cortisol 30 minutes after both short synacthen tests (HDT: 684 +/- 123, LDT: 669 +/- 119 nmol/l) and the peaks reached with the LDT (691 +/- 123 nmol/l) and the ITT (673 +/- 99 nmol/l). The only difference (P < 0.001) was found in the comparison of plasma cortisol peak reached with the HDT (802 +/- 142 nmol/l) with the other tests. Plasma cortisol levels obtained in the 5th percentile in each test were: at + 30 minutes: (HDT: 537, LDT: 489 nmol/l), peak: (HDT 649, LDT 498, ITT: 539 nmol/l).
CONCLUSIONS
Comparison of the plasma cortisol response at + 30 minutes with both short ACTH tests and the peak in the insulin tolerance test did not reveal differences. Each test, for each time point and for each biochemical method, requires its own minimum threshold of normality to assess the hypothalamo-pituitary-adrenal axis.