The level of cortisol in your blood, urine and saliva normally peaks in the early morning and declines throughout the day, reaching its lowest level around midnight. This pattern can change if you work a night shift and sleep at different times of the day. For most tests that measure cortisol levels in your blood, the normal ranges are:

A serum cortisol test may help in the diagnosis of two fairly uncommon medical conditions: Cushing syndrome and Addison disease.

Normal ranges are: 6 to 8 a.m.: 10 to 20 micrograms per deciliter (mcg/dL) Around 4 p.m.: 3 to 10 mcg/dL.

The serum cortisol (3-5 PM) test measures the level of cortisol, a hormone produced by the adrenal glands, in the bloodstream during the late afternoon. Here's how to interpret the results of a serum cortisol (3-5 PM) test: Normal Range: The normal range for serum cortisol levels in the late afternoon (3-5 PM) is typically lower than the morning levels, but exact reference ranges may vary depending on the laboratory and the specific assay method used for testing. In general, normal levels of serum cortisol during the late afternoon are typically lower than those observed in the morning, reflecting the normal diurnal variation of cortisol secretion. Interpretation: Normal Levels: Serum cortisol levels within the normal range during the late afternoon indicate normal adrenal function and diurnal variation. Cortisol levels are typically lower in the afternoon and evening compared to the morning. Low Levels (Hypocortisolism): Serum cortisol levels below the normal range during the late afternoon may indicate hypocortisolism, also known as adrenal insufficiency. Causes of hypocortisolism may include primary adrenal insufficiency (Addison's disease), secondary adrenal insufficiency (due to pituitary or hypothalamic dysfunction), chronic stress, or long-term corticosteroid therapy. High Levels (Hypercortisolism): Serum cortisol levels above the normal range during the late afternoon may indicate hypercortisolism, also known as Cushing syndrome. Causes of hypercortisolism may include adrenal tumors (such as cortisol-producing adenomas), pituitary tumors (causing excess adrenocorticotropic hormone, ACTH), exogenous corticosteroid use, or ectopic ACTH-producing tumors. Clinical Correlation: Interpretation of serum cortisol (3-5 PM) results should be done in conjunction with clinical assessment, including consideration of the patient's medical history, symptoms, and other laboratory findings. Additional tests or evaluations may be necessary to determine the underlying cause of abnormal serum cortisol levels and guide appropriate management. Dynamic Testing: In cases where serum cortisol levels are equivocal or inconclusive, dynamic testing may be performed to further evaluate adrenal function. This may include tests such as the cosyntropin stimulation test or the dexamethasone suppression test to assess adrenal responsiveness and differentiate between primary and secondary adrenal insufficiency or hypercortisolism.

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