Cortisol AM and PM Test in California

What this test measures

This test measures blood cortisol twice in one day to capture its natural daily variation. Cortisol is produced by the adrenal glands and normally peaks shortly after waking, then declines through the day. This rhythm supports metabolism, blood pressure regulation, and the body's response to stress. Comparing morning and afternoon values helps a provider assess whether the pattern is typical or whether further evaluation is needed.

Two blood samples are collected at times specified by the laboratory, usually in the morning and later in the afternoon. The laboratory measures total serum cortisol with an immunoassay. Related tests such as ACTH, cortisol-binding globulin, or free cortisol may be added when a provider wants more detail. Collection timing matters because cortisol changes quickly, so samples should be drawn as close to the scheduled times as possible.

People order this test when a provider suspects an adrenal hormone imbalance or wants to evaluate symptoms such as persistent fatigue, unexplained weight change, or blood pressure changes. It is a diagnostic support tool rather than a standalone answer. A qualified healthcare provider should interpret the results with your schedule, medications, sleep pattern, and other clinical information.