Cortisol deficiency is diagnosed by the adrenocorticotrophin (ACTH) stimulation test. This test measures cortisol levels in the blood before and after giving an injection of ACTH. Currently, the results of this test can only be reliably interpreted when it is carried out on people in non-stressful situations. Frequently the test is carried out in hospitalized patients in stressful situations, giving results that are hard to interpret.