Test Directory

The diagnosis of Cushing syndrome (CS) requires evidence of cortisol hypersecretion. While serum cortisol levels fluctuate unpredictably and are strongly dependent on concurrent cortisol-binding globulin (CBG) levels, a 24-hour urine specimen integrates the cortisol production for an entire day and is not affected by CBG. Urinary cortisol reflects the portion of serum-free cortisol filtered by the kidney, and correlates well with cortisol secretion rate. The most common causes of CS are pituitary adenoma (65% to 70%), adrenal tumor (15% to 20%), and ectopic CS (10% to 15%).

Specimen Type: 24 Hour Urine

Collection Container: 24 Hour Plastic Urine Container

Desired Specimen Volume: 100 mL

1. Collect 24-hour urine in a timed collection kit.
2. Specimen must be collected in a plastic container and refrigerated during collection.

1. Transfer 100 mL of urine to a sterile plastic cup (screw capped).

Transport to the laboratory refrigerated. 

See patient report.

Not useful in the evaluation of adrenal insufficiency (AI). Results in AI overlap with normal ranges. Increased in pregnancy and with oral contraceptives. Increased excretion may be found with pseudo-Cushing syndrome, trauma, or infection. Tetracyclines may cause false elevation of results.

• Urinary Free Cortisol