How is adrenal insufficiency diagnosed?

Stimulation Test. Cortisol levels vary widely between individuals, and by time of day and are affected by illness. So random levels may not be helpful. A stimulation test with an injection of Cortrosyn to make the adrenals release cortisol is used. Blood is drawn just before, and 30 and 60 minutes after the Cortrosyn injection. Stimulated levels above 18-20 usually indicate normal adrenal function.
Adrenal insufficienc. The acth stim test can be done. Cortisol, acth, aldosterone, renin, potassium, and sodium are tested before the decision is made whether the acth stimulation test needs to be performed. X-rays or ct of the adrenals may also be done. The best test for adrenal insufficiency of autoimmune origin, is measurement of 21-hydroxylase.