The effect of time of day testing and utility of 30 and 60 minute cortisol values in the 250 mcg ACTH stimulation test

We 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.