The ACTH test (also called the cosyntropin, tetracosactide, or Synacthen test) is a medical test usually ordered and interpreted by endocrinologists to assess the functioning of the adrenal glands stress response by measuring the adrenal response to adrenocorticotropic hormone (ACTH; corticotropin) or another corticotropic agent such as tetracosactide (cosyntropin, tetracosactrin; Synacthen) or alsactide (Synchrodyn).
Despite widespread use of the 250-mcg Cosyntropin test (ACTH test) for the diagnosis of adrenal insufficiency (AI), the effect of time of day and the utility of performing both 30- and 60-min serum cortisol values remains unclear.
Munro et al. found that outcomes from ACTH testing are not affected by time of day. Furthermore, using a 30-min cortisol level in isolation results in more than one in seven patients having a false positive diagnosis of AI; a 60-min value of ≥500 nmol/L alone may be sufficient to diagnose AI in >99% of cases 1).