Cortisol Blood Test in California

What this test measures

This test measures total serum cortisol at a single point in time. Cortisol is made by the adrenal glands and follows a daily rhythm, typically highest in the early morning and lowest late at night. It plays a central role in metabolizing carbohydrates, proteins, and fats and in helping the body respond to stress. A single value is most informative when the collection time is known, because reference ranges vary through the day.

A blood sample is collected by venipuncture, usually in the morning for a standard measurement. The laboratory analyzes cortisol with an immunoassay and reports the value with a time-specific reference range. When more detail is needed, providers may add ACTH, cortisol-binding globulin, a 24-hour urinary free cortisol collection, or salivary cortisol testing to see how the hormone behaves across the day.

People order cortisol testing when symptoms such as fatigue, weight change, mood changes, or blood pressure changes raise a question about adrenal function. It is also used to monitor cortisol-related conditions over time. The test supports evaluation rather than diagnosing on its own, so a qualified healthcare provider should interpret the result with your clinical picture.