Rapid ACTH Stimulation Test

Popular but often unnecessary test

  • – perform at any time of day or night
  • – obtain blood sample for baseline (random) plasma cortisol level
  • – give synthetic ACTH IV (Cosyntropin) 250 ug X11
  • – repeat plasma cortisol 1 hour after injection



  1. Random cortisol <10 ug/dL OR
  2. Increment in plasma cortisol <9 ug/dL after ACTH



  • – check random plasma cortisol
  • – if >=35 ug/dL – likely normal or adequate adrenal function
  • – if <10 ug/dL – evidence of adrenal suppression
  • – if 10-34 ug/dL – do rapid ACTH stim test as above

** In septic shock, do not check cortisol levels – trial of IV hydrocortisone is recommended if hypotension refractory to volume resuscitation.



Marino, P. (n.d.). The ICU book.

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