New guidelines for the diagnosis of Cushing’s
Posted by Michael Kleerekoper, MD, MACE July 7, 2008 07:37 AM
The Endocrine Society has just published new clinical guidelines for the diagnosis of Cushing’s syndrome.
The first recommendation is key: before any testing, obtain a complete drug history for any use of steroid preparations. I just spent three months on a Cushing’s workup before my patient asked whether the spinal injections he was getting every three months for control of back pain might be why the laboratory results weren’t making sense to me!
Consider Cushing’s in patients with unexpected osteoporosis or new onset hypertension, those with highly suggestive clinical features, and those with an adrenal incidentaloma.
For the initial testing the recommendations are 24 hour urine free cortisol (x2), or late night salivary cortisol (x2), or an overnight 1 mg dexamethasone suppression test. Few patients enjoy collecting urine in a bottle for 24 hours let alone twice. The overnight DST is straightforward but does require the patient to go the pharmacy for the tablet and present to the laboratory for blood work between 8 and 9 a.m. the next morning.
The late night salivary cortisol test is the most recently developed of the tests and seems the easiest for patients. On two separate occasions have the patient drool (yes that’s the word used in the guidelines) into a plastic tube. The sample is stable at room temperature for several weeks (I would not recommend waiting that long) and can be mailed to the testing laboratory.
As with all laboratory tests, be careful that specimens collected on separate days are sent to the same testing lab — assay methods and reference intervals do vary.
The guidelines, which are evidence based and very easy to read and follow, provide many more important details about both the initial screening I have just summarized and subsequent follow-up for positive or equivocal results.