Diagnosing adrenal insufficiency: which test is best--the 1-microg or the 250-microg cosyntropin stimulation test?

To review the available literature on the low-dose cosyntropin stimulation test (CST) for the diagnosis of primary and secondary adrenal insufficiency in both nonstressed and acutely ill patients.

We performed a MEDLINE search of all English-language literature, published between 1965 and 2007, in which the 1-microg and the 250-microg CSTs were compared in patients with primary and secondary adrenal insufficiency.

The majority of published evidence suggests that the 1-microg CST is more sensitive than the 250-microg CST for the diagnosis of secondary adrenal insufficiency in nonstressed patients. In patients with primary adrenal insufficiency, the low-dose CST is unlikely to add any diagnostic sensitivity to the high-dose CST. In critically ill patients, the 1-microg test is also likely to be more sensitive than the 250-microg test when an appropriate cutoff value is used (25 microg/dL).

The 1-microg CST with a cortisol level determined at 30 minutes after stimulation, with use of a cutoff level of 18 to 20 microg/dL in nonstressed patients and less than 25 microg/dL or an increment of less than 9 microg/dL from baseline in critically ill patients, is the best test that is currently available for establishing the diagnosis of secondary adrenal insufficiency.