Scientists have developed a better method of diagnosing Cushing’s syndrome that measures cortisol levels in a patient’s saliva. The enhanced testing protocol improves upon a method originally developed for urine cortisol, a study shows.
The study, “Clinical utility of an ultrasensitive late night salivary cortisol assay by tandem mass spectrometry,” was published in the journal Steroids.
Measuring levels of cortisol — the hormone that leads to Cushing’s syndrome when produced in excess — in saliva at night was one of the first diagnosis strategies for the disease. This test is known as late-night salivary cortisol, or LNSC.
“The appearance of late night cortisol secretion is one of the first indications of [Cushing’s syndrome],” the authors note.
The test uses conventional techniques called immunoassays and is still widely used due to its sensitivity, specificity, and the ease of obtaining a saliva sample. Over the years, scientists have developed more advanced methods with better sensitivity and specificity than immunoassays, such as tandem mass spectrometry (LC-MS/MS) assays. This method is capable of identifying a specific protein by analyzing its mass-to-charge ratio.
Now, a group of researchers sought to improve the LC-MS/MS method to measure salivary cortisol in both adult and pediatric patients. They also set out to review the method’s ability to diagnose Cushing’s syndrome.
The use of LC-MS/MS in the clinic is still rather limited due to a lack of standardized protocols and reference values for diagnosis, the team stated. So, they improved the LC-MS/MS protocol for measuring cortisol in the urine to allow for the measurement of much lower levels of cortisol in saliva.
The new protocol was tested on 110 patients, 74.5% of whom were women. The mean age for women and men was 35 and 37, respectively.
Based on this pool of patients, researchers established the cutoff value for diagnosing Cushing’s syndrome at 70 ng/dL. Below this value, patients have normal levels of salivary cortisol. A value of 70 or above is positive for Cushing’s syndrome.
Researchers said this value was “more appropriate as a frontline screening and diagnostic tool to rule out CS syndrome, with a resulting sensitivity and specificity of 100% and 92%, respectively.”
Overall, “the improved LC-MS/MS method is sensitive and specific with enhanced analytical performance and clinical diagnostic utility for screening Cushing’s syndrome. The assay may have broad clinical application due to its high sensitivity and wide dynamic range,” the study concluded.