Cortisol PM

The Cortisol PM test measures the amount of cortisol in your blood when it is collected in the afternoon or evening. Cortisol is a hormone made by the adrenal glands under the control of the pituitary hormone ACTH. Most cortisol in the bloodstream is bound to a carrier protein called cortisol-binding globulin, while a smaller unbound portion is biologically active.

Cortisol naturally follows a daily rhythm, tending to be higher after waking and lower later in the day. Measuring it in the afternoon or evening helps your clinician assess that daily pattern and how your adrenal glands are functioning in context.

This test helps evaluate symptoms related to too little or too much cortisol and is often paired with a morning cortisol or other dynamic tests. Your clinician may order it if you have fatigue, weakness, weight changes, low blood pressure, or features suggesting cortisol excess such as easy bruising or difficult-to-control blood pressure.

An afternoon or evening level can show whether the daily decline is preserved or altered, which can point toward conditions like adrenal insufficiency or hypercortisolism. Results can also guide monitoring of treatment and the need for further confirmatory testing.

Cortisol is normally lower later in the day compared with the morning, so your result is interpreted in light of that expected pattern, your symptoms, and any medicines you take. A single result rarely provides a final diagnosis.

If your level appears unexpectedly low or high, your clinician may repeat the test, compare it with a morning sample, or order confirmatory testing such as an ACTH stimulation test, dexamethasone suppression testing, or late-night salivary cortisol. Do not stop steroid medications on your own; always discuss next steps and medication changes with your care team.