Cortisol, Serum AM and PM

Cortisol is your body's main stress hormone, and it normally peaks in the morning to help you wake up and then falls throughout the day. Measuring it at two time points helps your doctor check whether your adrenal glands are making too much, too little, or the right amount at the right times.

When elevated: Persistently elevated AM cortisol, particularly when accompanied by a blunted PM decline, raises concern for endogenous hypercortisolism (Cushing syndrome) or significant physiologic or psychological stress load, both of which are associated with increased risk of metabolic syndrome, hypertension, osteoporosis, immune suppression, and neuropsychiatric effects. A single elevated value in the context of acute illness or stress is generally not diagnostic and requires repeat testing under basal conditions. Confirmatory testing with 24-hour urine free cortisol, late-night salivary cortisol, or low-dose dexamethasone suppression testing is typically required before a diagnosis of hypercortisolism is established. When low: A low AM cortisol (generally below 3–5 mcg/dL) is concerning for adrenal insufficiency, which may be primary (Addison disease, adrenal destruction), secondary (pituitary ACTH deficiency), or tertiary (hypothalamic CRH deficiency, often from exogenous glucocorticoid use). Adrenal insufficiency is a potentially life-threatening condition, particularly during physiologic stress, and warrants prompt evaluation including ACTH stimulation testing and measurement of plasma ACTH. Borderline low values (approximately 5–10 mcg/dL) are indeterminate and require dynamic testing for definitive assessment.

Cortisol AM/PM pattern is highly relevant to athletes because chronic training stress and inadequate recovery can blunt or flatten the normal circadian rhythm, impairing adaptation and increasing injury/illness risk. Monitoring this diurnal variation helps assess whether training load is sustainable and whether the HPA axis is recovering adequately between sessions.