Dexamethasone Test May Show Cushing’s Before Bariatric Surgery

Of 753 people tested, hypercortisolism was confirmed with additional tests in 6

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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Not many people who are very obese have Cushing’s syndrome, but a low-dose dexamethasone test may help distinguish who has the disease from who doesn’t before weight loss surgery, a Turkish study has reported.

The study, “Assessment of the diagnostic performance of the 1 mg dexamethasone suppression test in class 3 obese patients,” was published in Endocrine Regulations.

Cushing’s syndrome occurs as a result of hypercortisolism, which is when the hormone cortisol is found at high levels in the body. One of the telltale symptoms of Cushing’s is weight gain and fat accumulation at the back of the neck, shoulders, and around the chest and waist.

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Bariatric surgery, also known as weight loss surgery, is sometimes used to treat people who are very obese. Candidates for it may have symptoms nearly identical to Cushing’s, yet they may not have the disease. When this happens, they’re said to have pseudo-Cushing’s syndrome.

Being able to tell people who have pseudo-Cushing’s from those who have Cushing’s ahead of bariatric surgery is important to ensure patients receive proper treatment.

Researchers in Turkey evaluated how common Cushing’s is among people who are interested in bariatric surgery. They also evaluated the performance of the low-dose dexamethasone test as a diagnostic method on these patients.

Dexamethasone is a man-made steroid that shuts off cortisol production in healthy people. It’s possible to tell if the body is making more cortisol than normal when its levels fail to drop in response to a low dose (1 mg) of dexamethasone.

The study included 753 people (545 women, 208 men) who were a mean age of 40 and had a mean body mass index (BMI) of 46 kilograms per square meter.

The BMI is a measure of body fat. People who have a BMI of 30 or higher fall within the obesity range. Obesity can also be divided into three classes, with those having a BMI of 40 or higher falling in the highest class (class 3) of severe obesity.

Of the 753 people, 24 (3.18%) failed to show a drop in cortisol levels in response to 1 mg of dexamethasone. Hypercortisolism was confirmed by additional tests in six (0.79%) of them. This finding showed the prevalence of Cushing’s syndrome among people with severe obesity may be “close to [that of] the non-obese population,” the researchers wrote.

Additional tests included a 24-hour urinary test to measure the amount of cortisol in urine over a day and a midnight serum test to measure the amount of cortisol in the blood late at night when its values are normally low.

The specificity of the low-dose dexamethasone test in these patients was 97.5%, with a cutoff value of 1.8 micrograms per deciliter. This means that 97.5% of people who do not have hypercortisolism (or a cortisol level less than 1.8 micrograms per deciliter) will test negative.

The low-dose dexamethasone test was “an adequate test with a very good performance in Cushing’s syndrome screening in this patient group,” the researchers wrote.