Cortisol (Serum – 4 PM) is a blood test that measures the level of cortisol in your bloodstream in the afternoon (typically around 4 PM). Cortisol is a key stress hormone made by the adrenal glands (small glands that sit on top of the kidneys). It helps regulate energy, blood pressure, blood sugar, immune response, and inflammation.

Cortisol follows a natural daily pattern called the diurnal cortisol rhythm or adrenal rhythm: it is usually highest in the early morning, then gradually decreases throughout the day and is lower in the late afternoon and evening. Measuring cortisol specifically at 4 PM helps your clinician see whether your afternoon level is appropriately lower compared with your morning level (often checked with an 8 AM cortisol), and whether your daily cortisol pattern is normal.

What results can mean (in plain language): A 4 PM cortisol result is interpreted in the context of the lab’s reference range and your symptoms, medications, and other tests.

Higher-than-expected afternoon cortisol may suggest your body is producing too much cortisol or that your cortisol isn’t dropping normally during the day. This can be seen with conditions such as Cushing syndrome, prolonged physiologic stress, severe illness, or with certain medications (including steroid medicines). It may also be influenced by sleep disruption, shift work, or acute pain and anxiety around the time of the draw.

Lower-than-expected afternoon cortisol can be seen when the adrenal glands are not producing enough cortisol (adrenal insufficiency), when pituitary signaling to the adrenal glands is reduced, or after stopping long-term steroid therapy. Because cortisol levels naturally vary during the day, a single afternoon value usually does not confirm a diagnosis by itself—your clinician may compare it with a morning cortisol and/or order confirmatory testing.

This test is commonly ordered to evaluate cortisol afternoon levels as part of a broader assessment of adrenal function and daily cortisol rhythm. It may be recommended when symptoms or health history suggest abnormal cortisol production—either too high or too low—or when monitoring known adrenal or pituitary disorders.

Your clinician may order a 4 PM serum cortisol test if you have symptoms that could be related to high cortisol (excess stress hormone), such as:

Unexplained weight gain (especially around the abdomen), facial rounding, easy bruising, thin skin, purple stretch marks, acne, muscle weakness, high blood pressure, high blood sugar/diabetes, mood changes (anxiety, irritability, depression), trouble sleeping, and increased infections or slow wound healing.

It may also be ordered if you have symptoms that could be related to low cortisol (adrenal insufficiency), such as:

Unusual fatigue, weakness, dizziness (especially when standing), low blood pressure, unintentional weight loss, nausea/vomiting, abdominal pain, salt cravings, low blood sugar, or darker skin pigmentation (in some forms of adrenal disease).

Additional common reasons for testing include:

Evaluating suspected Cushing syndrome or adrenal insufficiency, checking adrenal recovery after long-term steroid treatment (e.g., prednisone, dexamethasone, inhaled or topical steroids in some cases), investigating irregular sleep schedules/shift work that may alter cortisol patterns, and interpreting other hormone results as part of an endocrine workup.

Important notes that can affect results: Cortisol can be influenced by recent illness, intense exercise, pregnancy, estrogen-containing birth control, and steroid medications. Always tell your clinician and the lab about all prescription drugs, over-the-counter medicines, and supplements you take. Your provider may recommend pairing this test with a morning cortisol, ACTH level, or dynamic testing (such as an ACTH stimulation test or dexamethasone suppression test) depending on your situation.

• Cushing syndrome (hypercortisolism), including adrenal, pituitary (Cushing disease), or ectopic ACTH sources
• Adrenal insufficiency (Addison disease and secondary/tertiary adrenal insufficiency)
• Pituitary disorders affecting ACTH production
• Adrenal tumors or adrenal hyperplasia (benign or malignant)
• Medication-induced adrenal suppression from chronic glucocorticoid use (e.g., prednisone)
• Chronic stress and sleep-related circadian rhythm disruption (may alter diurnal cortisol rhythm)

• Assessing adrenal rhythm and daily cortisol patterns (diurnal cortisol rhythm tracking)
• Supporting evaluation of persistent fatigue, low energy, or stress-related symptoms (stress hormones assessment)
• Monitoring endocrine health when concerned about cortisol-related weight, blood pressure, or blood sugar changes
• Guiding care for long-term steroid users by checking for possible adrenal suppression during tapering
• Exploring contributors to chronic inflammation and immune changes when clinically appropriate
• Supporting overall hormonal and metabolic wellness evaluation alongside other labs (e.g., morning cortisol, ACTH, glucose, lipids)