The Accuracy of Late Night Urinary Free Cortisol/Creatinine and Hair Cortisol in Cushing's Syndrome Diagnosis

24h-Urine free cortisol (24h-UFC) and other screening tests may turn out normal in Cushing's syndrome (CS) patients, probably due to high variability and cyclicity in cortisol secretion. To rule out cyclic cortisol secretion, the recommendation is to repeat 24h-UFC measurements on different and several occasions. As 24h-UFC is technically inconvenient, especially in the elderly and in women, compliance may not be optimal, and results could be falsely low especially if collection is not properly conducted.

Alternatively, the status of cortisol circadian rhythm and urinary cortisol secretion may be assessed in a non-invasive and more convenient manner through the measurement of late evening urinary free cortisol concentration/creatinine concentration (Late-UFC). These measurements have been useful in screening outpatients for CS, but their performances have not been properly and enough validated.

It appears that the assessment of Late-UFC can offer a non-invasive and convenient diagnostic tool for evaluating cortisol circadian rhythm and urinary cortisol secretion in ambulatory populations, especially in the case of patients for whom 24h-UFC should be repeated yet is technically not convenient to perform.

Hair sample testing has gained increasing attention and recognition over the last 20 years, especially for detecting illegal drug use and for other forensic purposes. This is because hair provides a relatively long-term retrospective record of levels of various bio-markers in the body.

In light of the foregoing evidence, it has been suggested that hair cortisol measurement could be a novel method for assessing dynamic systemic cortisol exposure, and could provide unique historical information on variation and cyclicity in cortisol exposure.