Cortisol Free Urine, 24 Hours

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Subject: Cortisol Free Urine, 24 Hours

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Definition

  • Cortisol free urine, 24-hour, or urinary free cortisol provides a direct and reliable practical index of cortisol secretion. It is an integrated measure of serum free cortisol level that is not affected by body weight.

  • Normal range:

    • Males: <60 μg/day; <32 μg/g creatinine

    • Females: <45 μg/day; <45 μg/g creatinine

Use

  • Aids in the diagnosis of hypercortisolism caused by Cushing syndrome

  • Adrenal insufficiency (limited usefulness)

  • Assisting in diagnosing acquired or inherited abnormalities of 11β-hydroxy steroid dehydrogenase (cortisol-to-cortisone ratio)

  • Diagnosis of pseudohyperaldosteronism due to excessive licorice consumption

Interpretation

  • Cortisol free urine, 24-hour, is increased in Cushing syndrome. The patient can be assumed to have Cushing syndrome if basal urinary cortisol excretion is more than 3 × the upper limit of normal and one other test is abnormal.

  • This result is found in 95% of cases of Cushing syndrome. Values <100 μg/24 hours exclude the diagnosis, and values >300 μg/24 hours confirm the diagnosis. If values are intermediate, a dexamethasone suppression test is indicated.

  • It is decreased in adrenal insufficiency.

Limitations

  • Urinary cortisol may be detected by antibody-based (immunoassays) or structurally based (HPLC-MS) tests, and the immunoassays may be less specific because antibodies may cross-react with similar steroids.

  • An increase is the most useful screening test (best expressed as per gram creatine, which should vary by <10% daily; if variation is >10%, two more 24-hour specimens should be collected). Values should be measured in three consecutive 24-hour specimens to ensure proper collection and account for daily variability, even in Cushing syndrome.

  • Increased values may occur in depression, chronic alcoholism, eating disorders, and polycystic ovary syndrome but do not exceed 300 μg/24 hours.

  • Various drugs (e.g., carbamazepine, phenytoin, phenobarbital, primidone) will falsely elevate free cortisol levels.

  • Acute and chronic illnesses can increase free cortisol levels.

  • Renal disease due to decreased excretion may falsely lower the levels of free cortisol.

 
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