Updated Diagnostic Cortisol Values for Adrenal Insufficiency

Inclusion Criteria for healthy volunteers: \- Male and female outpatients 18 years or older without prior diagnosis of primary or central adrenal insufficiency Inclusion Criteria for patients with known adrenal insufficiency: \- Males and females 18 years or older with established diagnosis of primary or central adrenal insufficiency as previously documented in the electronic medical record by a failed CST (peak cortisol level \< 18 μg/dL) or morning serum cortisol \< 3 mcg/dL with an appropriate clinical circumstance (e.g., Sheehan's syndrome, pituitary surgery and/or irradiation, bilateral adrenalectomy, etc.) that strongly supports a true diagnosis of primary or central adrenal insufficiency, and current use of physiologic, replacement dose glucocorticoids. Inpatients with non-critical illness and outpatients are eligible Inclusion Criteria for patients with suspected adrenal insufficiency: \- Males and females 18 years or older with suspected diagnosis of primary or central adrenal insufficiency by any cause based on clinical evaluation by a study team member. Inpatients with non-critical illness and outpatients are eligible Exclusion Criteria for all groups: * Moderate to severe liver impairment or abnormal albumin or cortisol binding globulin concentrations * Renal impairment with estimated Glomerular Filtration Rate (eGFR) \< 60 mL/min/1.73m2 and/or diagnosis of nephrotic syndrome * Pregnancy or nursing mothers * Use of estrogen preparations * Uncontrolled major depressive disorder or psychiatric diseases, severe malnutrition, eating disorders, chronic fatigue syndrome (disorders that alter hypothalamic-pituitary-adrenal (HPA) axis function) * Use of any medications that induce hepatic cytochrome P-450 enzymes, e.g., barbiturates, phenytoin, rifampin, aminoglutethimide and mitotane * Active medical treatment of Cushing's syndrome (status-post surgical treatment is acceptable) * Uncontrolled hypo- or hyperthyroidism * Use of biotin within the past 72 hours * Regular alcohol and/or cannabis use * History of bilateral adrenalectomy * Treatment for validated primary adrenal insufficiency for greater than 6 months * Be assessed by the investigators as unsuitable for participation in this study for any reason Additional Exclusion Criteria for healthy volunteers only: * Regular use of any oral glucocorticoid (e.g. hydrocortisone, prednisone, dexamethasone) within 6 weeks of the screening visit * Use of oral or nasal steroid (glucocorticoid) inhalers in the past 2 weeks * Regular use of any steroid creams, gels, ointments, or lotions * Use of steroid (glucocorticoid) injections in the past 6 months (healthy volunteers) * Regular use of opioids * Regular use of suboxone * Regular use of megestrol acetate