Urinary free cortisol measurement most accurate first-line test for Cushing's syndrome diagnosis
Measuring 24-hour urinary free cortisol with liquid chromatography-mass spectrometry is the most accurate first-line diagnostic tool for diagnosing Cushing’s syndrome in adults, according to research published in The Journal of Clinical Endocrinology & Metabolism.
Filippo Ceccato, MD, of the University Hospital of Padova, Italy, and colleagues analyzed data from 137 adults from 2012 to 2014 (108 women; mean age, 41 years) with clinical conditions suggestive of hypercortisolism. Within the cohort, 38 had a confirmed diagnosis of Cushing’s syndrome (27 women); 99 did not have the diagnosis. In all patients, researchers measured 24-hour urinary free cortisol with liquid chromatography-tandem mass spectrometry (LC-MS/MS), late-night salivary cortisol with a radio-immunometric method and serum cortisol with a 1-mg dexamethasone suppression test. Researchers performed all three tests on patients within 2 weeks to avoid fluctuations in cortisol production.
Researchers found that using LC-MS/MS to measure urinary free cortisol revealed both a combined higher positive ratio (10.7) and a lower negative likelihood ratio (0.03) among the three first-line tests.
For the 1-mg dexamethasone suppression test, researchers found a cutoff of 138 nmol/L revealed the best specificity (97%), whereas the 50 nmol/L cutoff confirmed the best sensitivity (100%). For the late-night salivary cortisol test, researchers found a cutoff of 14.46 provided a sensitivity of 84% and specificity of 89%. For urinary free cortisol, a cutoff of 170 nmol during 24 hours provided a sensitivity of 97% and specificity of 91%.
After using a receiver operating characteristic (ROC)-contrast analysis to compare the power of each test alone and combined with one another, the urinary free cortisol assay was at least as good as all the other possible combinations, according to researchers.
“This result is rather surprising because some authors have recently advocated replacing [the urinary free cortisol] assay with other tests,” the researchers wrote. “Our findings go against such a hypothesis, probably because we used LC-MS/MS in our routine clinical practice for all patients, meaning that high [urinary free cortisol] concentrations pointed to a high likelihood of [Cushing’s syndrome].”
Researchers also observed higher urinary free cortisol levels in men with Cushing’s syndrome, as well as greater cortisol suppression in the 1-mg dexamethasone suppression test in women, but noted that sex did not affect the diagnostic accuracy of tests.
“Choosing between valid tests for ruling out [Cushing’s syndrome] in high-risk populations requires an understanding of their diagnostic performance in different clinical settings,” the researchers wrote. “We recommend measuring [urinary free cortisol] with LC-MS/MS as the first-line screening test for the diagnosis of [Cushing’s syndrome], and then confirming hypercortisolism with the 1-mg [dexamethasone suppression test] or late-night salivary cortisol assay.” – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.