I can understand your concern about your daughter's health.
The short Synacthen test (SST) is used to evaluate adrenal glucocorticoid secretion in response to synthetic ACTH (also known as tetracosactide or Synacthen). Traditionally, after a baseline cortisol and ACTH, two plasma cortisol samples have been taken after i.v. or i.m. administration of Synacthen 250 μg, one at 30 min and one at 60 min. However practice varies and some physicians only take one cortisol measurement at 30 min.
95% passed if the 30 min cortisol value alone was assessed, giving a false negative (i.e. failed test) rate of 5%.
This means that there is a very low chance of less than 5 % of this test being wrongly negative.
I would recommend that if she is very much sure about her symptoms, a repeat test with two samples being taken at 30 & 60 minutes both would be able to help her out in a better way to diagnose if she has adrenal failure,
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Dr. Gupta, MD