Cortisol Serum (7 to 9 AM)

If your morning cortisol is 7 µg/dL (≈193 nmol/L), that's generally within the normal but low‑end range and usually not alarming if symptoms are absent. If the result is 7 nmol/L, that's very low and could indicate adrenal insufficiency. Confirm the units, repeat testing, and discuss symptoms with your clinician—further evaluation (including ACTH stimulation) may be needed.

Cortisol testing is done before 9am because cortisol follows a circadian rhythm, peaking in the early morning after waking. Measuring cortisol at its natural peak improves diagnostic accuracy for conditions like adrenal insufficiency or Cushing’s syndrome. Later measurements can be lower and lead to false reassurance. Early sampling, ideally soon after waking, also reduces interference from stress, illness, or medications.

An 8am cortisol test measures blood cortisol at its early-morning peak to evaluate adrenal function and the hypothalamic–pituitary–adrenal axis. It helps detect adrenal insufficiency (low cortisol) or Cushing’s syndrome (high cortisol), and guides further testing or treatment when patients have fatigue, unexplained weight change, muscle weakness, low blood pressure, or abnormal electrolytes. Results are interpreted with clinical context and sometimes follow-up tests.

Cortisol is highest in the early morning, typically around 6–8 AM, peaking about 30–45 minutes after waking (the cortisol awakening response). This morning surge helps increase alertness and mobilize energy. Levels then decline through the day, reaching their lowest point late evening to early night (around midnight), supporting sleep onset.

High cortisol can cause weight gain (especially around the abdomen and face), increased appetite, and muscle weakness. Other signs include high blood pressure, mood changes (anxiety, depression, irritability), sleep problems and fatigue, poor concentration and memory, thin skin with easy bruising, slow wound healing, irregular periods or reduced libido, and greater susceptibility to infections; long-term excess may cause osteoporosis.

Best time to measure cortisol is early morning, typically around 7–9 AM (often ~8 AM) when levels peak; samples are usually taken fasting and before steroid medications. For suspected Cushing’s or abnormal daily rhythm, late-night (around midnight) salivary or serum cortisol, or a 24‑hour urinary free cortisol, may be used. Follow your clinician’s instructions about timing and medications.