Endocrine Abstracts

Background: Despite the widespread use of the 250-μg Cosyntropin test (ACTH test) for the diagnosis of adrenal insufficiency (AI), the effect of timing of the test on 30- vs. 60-min serum cortisol values remains unclear. Also, there is limited evidence comparing the value of performing both 30- and 60-min cortisol levels.

Methods: We conducted a retrospective cohort study of all ACTH tests conducted at the Halifax Neuropituitary Program, Nova Scotia, Canada, from January 2006 to April 2016. Data were collected on serum cortisol levels at 0, 30 and 60 min after ACTH administration, time of testing, age, gender, and indication for testing.

Results: There were 345 tests performed and divided by time of day (8:00–10:00 AM, 10:01 AM–12:00 PM, and after 12:00 PM). There were no significant differences in age, gender, or indication for testing between groups. The baseline 0-min mean (nmol/l) cortisol levels were lower later in the day (269, 239, 213, respectively; P=0.002), but there were no differences in mean (nmol/l) cortisol levels at 30 (565.5, 553, 529.5, respectively; P=0.38) and 60 min (635, 620, 616, respectively; P=0.79) between groups. When comparing 30 vs. 60-min values while using a cut-off of >500 nmol/l, 48 patients (13.9%) failed to reach the cut-off at 30 min but met the cut-off at 60 min. Conversely, only two patients (0.6%) who met the cut-off at 30 min failed to reach it at 60 min.

Conclusion: Our data suggest that the outcome of the ACTH test is not affected by time of day. Furthermore, if using a 30-min cortisol level in isolation, more than one in seven patients would have a false positive diagnosis of AI. Additionally, our data suggest that a 60-min value alone may be sufficient to diagnose AI in >99% of cases.