Adrenocorticotropin stimulation test in congenital adrenal hyperplasia: comparison between standard and low dose test

The aim of the study was to compare the response between the standard and low dose adrenocorticotropin (ACTH) test for patients with congenital adrenal hyperplasia (CAH). The authors employed a 2-by-2 crossover design and enrolled 16 patients, 14 girls and 2 boys, aged between 1.4 months and 15 years. Steroid treatment was stopped 24 hours before each test was conducted. The standard ACTH (250 microg) test was performed followed by the low dose test (1 microg) in eight patients; the other eight underwent the low dose ACTH test first followed by the standard one. The cortisol and 17-hydroxyprogesterone (17-OHP) levels in each patient varied unpredictably between the two tests. The cortisol responses to the low dose ACTH at 30 and 60 minutes were lower than at time zero; in contrast to the 60-minute peak cortisol response to the standard dose. The serum 17-OHP in all specimens was more than 10,000 ng/dl (300 nmol/L), with the peak response at 60 minutes in both groups. Both the low dose and standard dose ACTH test indicated adrenal insufficiency and the high 17-OHP levels were diagnostic of 21- hydroxylase (21-OH) deficiency. If the low dose ACTH test becomes the "standard" ACTH test, the diagnosis of 21-OH deficiency would probably not be missed.