Cortisol is a steroid hormone produced by the adrenal glands, regulated by ACTH from the pituitary.

Levels follow a diurnal rhythm, peaking in the morning and reaching their lowest in the evening.

Measuring PM cortisol helps assess whether this rhythm is preserved or disrupted.

Clinical uses include:

Diagnosing Cushing’s syndrome (loss of normal diurnal variation, persistently high cortisol).

Detecting adrenal insufficiency (Addison’s disease).

Evaluating pituitary or adrenal gland disorders.

Monitoring patients on steroid therapy.

Often performed alongside AM cortisol, ACTH stimulation test, and dexamethasone suppression test for comprehensive evaluation.

Analyte: Serum Cortisol (µg/dL).

Normal Range (varies by lab, evening sample): ~2–9 µg/dL (lowest levels in late evening).

Abnormal Findings:

High PM cortisol: Cushing’s syndrome, adrenal hyperplasia, pituitary adenoma, stress.

Low PM cortisol: Addison’s disease, adrenal insufficiency, pituitary dysfunction.

Clinical Use:

Provides a marker of adrenal gland function and circadian rhythm.

Helps guide diagnosis and monitoring of endocrine disorders.

Supports critical care and metabolic evaluations.