Acute adrenal insufficiency should be suspected when hypotension occurs in a patient with chronic adrenal insufficiency or in association with any of the known causes of adrenal insufficiency (see Table 76-1). When it is suspected, a blood sample should be drawn immediately for the measurement of plasma cortisol. Because plasma cortisol concentrations range between 20 and 120 μg/dL during severe stress or shock in patients with normal adrenal function, a plasma cortisol concentration of <20 μg/dL favors a diagnosis of adrenal insufficiency. Treatment should not wait for the result but should be initiated as soon as the blood sample for cortisol has been obtained. Initial treatment should consist of the intravenous administration of 100 mg of hydrocortisone in association with steps to maintain blood pressure. Hydrocortisone, 100 mg every 6 hours, should be administered until the crisis is past or the diagnosis is excluded. Steps designed to establish a definitive diagnosis should be instituted immediately.