Understanding High Urine Cortisol with Normal Blood Cortisol: Causes & Implications

Cortisol tests may be ordered by a physician to investigate suspected endocrine disorders. Both elevated cortisol, as in Cushing’s syndrome, and decreased cotisol, as in Addison’s disease, can lead to significant problems in multiple body systems.

Blood Test

• A blood test for cortisol is normally performed in the morning. The blood sample is usually collected from the large vein at the inside of the elbow.

Urine Test

• Urine cortisol tests require the collection of urine over a 24-hour period. The total amount of cortisol is the determined over the course of the entire day.

Normal Values

• Blood values of cortisol are normally between 6 and 23 micrograms per deciliter when collected at 8 a.m. Normal 24-hour urine values are 10 to 100 micrograms per deciliter.

Cortisol Release

• Cortisol is released in a cyclical rhythm driven by an internal biological clock. Peak stimulation occurs at approximately 4 a.m.

Significance

• A single blood sample may not accurately reflect cortisol levels as peak values may have occurred at a different point during the daily cycle, producing a normal blood sample when cortisol levels are actually elevated. The elevation would be detected, however, by 24-hour urine cortisol levels.