BOSTON – A random morning serum cortisol above 11.1 mcg/dL safely rules out adrenal insufficiency in both inpatients and outpatients, according to a review of 3,300 adrenal insufficiency work-ups at the Edinburgh Centre for Endocrinology and Diabetes.
The finding could help eliminate the cost and hassle of unnecessary adrenocorticotropic hormone (ACTH) stimulation tests; the investigators estimated that the cut point would eliminate almost half of them without any ill effects. “You can be very confident that patients aren’t insufficient if they are above that line,” with more than 99% sensitivity. If they are below it, “they may be normal, and they may be abnormal.” Below 1.8 mcg/dL, adrenal insufficiency is almost certain, but between the cutoffs, ACTH stimulation is necessary, said lead investigator Dr. Scott Mackenzie, a trainee at the center.
Dr. Scott Mackenzie
In short, “basal serum cortisol as a screening test ... offers a convenient and accessible means of identifying patients who require further assessment,” he said at the annual meeting of the Endocrine Society.
Similar cut points have been suggested by previous studies, but the Scottish investigation is the first to validate its findings both inside and outside of the hospital.
The team arrived at the 11.1 mcg/dL morning cortisol cut point by comparing basal cortisol levels and synacthen results in 1,628 outpatients. They predefined a sensitivity of more than 99% for adrenal sufficiency to avoid missing anyone with true disease. The cut point’s predictive power was then validated in 875 outpatients and 797 inpatients. Morning basal cortisol levels proved superior to afternoon levels.
The investigators were thinking about cost-effectiveness, but they also wanted to increase screening. “We may be able to reduce the number of adrenal insufficiency cases we are missing because [primary care is] reluctant to send people to the clinic for synacthen tests” due to the cost and inconvenience. As with many locations in the United States, “our practice is to do [ACTH on] everyone.” If there was “a quick and easy 9 a.m. blood test” instead, it would help, Dr. Mackenzie said.
Adrenal insufficiency was on the differential for a wide variety of reasons, including hypogonadism, pituitary issues, prolactinemia, fatigue, hypoglycemia, postural hypotension, and hyponatremia. Most of the patients were middle aged, and they were about evenly split between men and women.
There was no outside funding for the work, and the investigators had no disclosures.