Diagnostic value of 9 am plasma adrenocorticotrophic hormone concentrations in Cushing's disease.

Morning plasma adrenocorticotrophic hormone (ACTH) concentrations were measured in 58 normal subjects and seven patients with pituitary-dependent Cushing's syndrome (Cushing's disease). Particular note was taken of the time of venepuncture. The range of values for the normal subjects irrespective of timing was 9-77 ng/l. The range between 9 0 am and 9 30 am was 9-24 ng/l. In the patients with Cushing's disease the ACTH concentrations were in the range 39-109 ng/l. To distinguish patients with Cushing's disease from normal subjects it is therefore important to define accurately the 9 am normal range, since these results show no overlap.