How useful is 24 hour Urinary Free Cortisol as a screening tool for Cushing’s syndrome?

Introduction
Cushing’s syndrome (CS) is a rare disease that can be difficult to diagnose.
24 hour urinary free cortisol (UFC) is one of the reliable screening tests to
diagnose CS. The Endocrine Society recommends against widespread screening
for CS. It advises to screen those patients presenting with multiple and
progressive features (easy bruising, facial plethora, proximal myopathy and
striae) of CS, in addition to patients who experience unusual features for their age
(osteoporosis, hypertension).
Methods
A retrospective audit was done to assess our practice of requesting 24 hour UFC in
patients attending Diabetes, Endocrine and Weight management clinics in MidYorkshire
Hospital over 3 years. 356 patients were eligible for final analysis.
Results
66.6% of the patients were females and 33.4% were men. The mean age in our
cohort was 44.9 years and the mean BMI was 35.8 Kg/m2
. 61% of the patients had
hypertension and 21.6% had diabetes. The reason for requesting 24 h UFC is as
follows: 41% for secondary hypertension, 21% for obesity, 14% for adrenal
incidentaloma, 5% for clinical suspicion of Cushing’s, 19% for other reasons
(hirsutism, uncontrolled diabetes, flushing). Thirty one patients (8.7%) had
clinical features of Cushing’s syndrome. Among those with Cushingoid features,
seven patients (22.5%) had raised 24 hour UFC and four patients (12.9%) were
finally diagnosed with CS. 325 patients had 24 h UFC test requested despite
lacking clinical features of Cushing’s. Twenty nine patients (8.9%) had initial
positive 24 h UFC. Only two patients (0.6%) were finally diagnosed with CS.
These two patients had the test because of adrenal incidentaloma.
Conclusion
We did not find any benefit of requesting 24 h UFC in those who did not have
classic Cushingoid features. This audit confirms that it we need to adhere to the
Endocrine society guidelines on investigations for CS.