Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (663 page)

   Diagnosis of Addison disease, CAH, Cushing syndrome, adrenal carcinoma, and ectopic ACTH syndrome

   Interpretation

Increased In

   Addison disease

   CAH

   Pituitary-dependent Cushing disease

   Ectopic ACTH–producing tumors

   Nelson syndrome

Decreased In

   Secondary adrenocortical insufficiency

   Adrenal carcinoma

   Adenoma

   Hypopituitarism

   Limitations

   Plasma levels of ACTH exhibit a significant diurnal variation. ACTH is normally highest in the early morning (6–8
AM
) and lowest in the evening (6–11
PM
). Cortisol levels are frequently measured at the same time as ACTH.

   Because ACTH is released in bursts, its levels in the blood can vary from minute to minute.