NATIONAL HARBOR, MD. – If you’re one of the many physicians with an X-ray absorptiometry machine collecting dust in the nether regions of your clinic, recent findings from a small pilot study might interest you.
Dr. Steven R. Goldstein said he found that roughly 20% of postmenopausal women whose body mass index (BMI) measurement indicated they had a normal weight actually had body fat measurements greater than the 75th percentile when their body fat was assessed using a X-ray absorptiometry (DXA) scanner.
Dr. Steven R. Goldstein
Similarly, about a fifth of postmenopausal women in the study whose BMI indicated they were in the overweight range actually had DXA scanner readings indicating their percentage of body fat placed them below the 25th percentile.
“When you have 20% in each group, that’s not a tiny number,” Dr. Goldstein said in an interview at this year’s annual meeting of the North American Menopause Society. “BMI or weight alone does not always predict metabolic health.”
BMI, a measurement first created for use by insurance actuaries by Belgian mathematician Adolphe Quetelet in the mid-1800s, has come under scrutiny across the specialties in recent years, particularly since 1998 when the Centers for Disease Control and Prevention aligned with the World Health Organization determined that the criteria for being overweight was a BMI of 25 kg/m2 instead of 27.8 kg/m2.
“This instantly rendered 29 million previously healthy Americans as now being overweight,” Dr. Goldstein, a professor of obstetrics and gynecology at New York (N.Y.) University Langone Medical Center, told the audience.
Additionally, as one audience member noted during the question and answer period of the presentation, many members of nonAnglo populations, such as those from Mexico and Central America, are strong, healthy endomorphs, even though their BMIs would indicate otherwise.
“Most people don’t think about the fact that BMI is 170 years old and that with it, a 25-year-old man who weighs 150 pounds and is 5 foot 8 inches, has the same BMI as a 60-year-old woman who also weighs 150 pounds,” Dr. Goldstein said in an interview. “And yet, it’s used almost as another vital sign.”
Instead, Dr. Goldstein said that data from DXA scanners could be used by insurance companies to make more accurate decisions about obesity-related medical procedures, such as bariatric surgery. Studies have shown that some adults considered normal weight have cardiovascular abnormalities, and some considered obese are metabolically healthy (Arch. Intern. Med. 2008;168:1617-24).
“Using BMI, some people are being denied bariatric surgery when they need it, but there may be other people who are having the surgery who don’t actually need it,” Dr. Goldstein said.
The scanners also have met with some darker times, especially as reimbursements for the technology primarily used to determine bone mineral density in an aging population have fluctuated over the years, leaving many physicians with thousands of dollars in equipment they no longer use for fear they will not be paid for their time.
DXA scanners use two different energy levels that are absorbed differently by bone and lean and fat tissues, then uses the differences between them to determine the amount of lean and fat tissue across the entire body.
Dr. Goldstein and his colleagues analyzed DXA data taken from 50 postmenopausal women who visited his clinic for a routine bone mass DXA scan. The scanner software was used to calculate the women’s body fat percentile according to age and sex. Women who were between the 25th and 75th percentile were considered to have “normal” body fat, whereas below the 25th percentile or above the 75th percentile was considered abnormally lean or heavy, respectively. The measurements then were compared with the women’s BMI measurements.
Just over 18% of the cohort had normal BMI readings but placed above the 75th percentile for body fat when measured by the scanner. Conversely, 22% of women in the lowest percentile for body fat per their DXA scan also had normal BMI weight. Twenty-three percent of women considered overweight according to their BMI fell into the normal range for DXA body fat results. All of the women in the study considered obese by BMI were in the 100th percentile using the DXA scanner.
“DXA determination of body fat percentile seems like a reasonable and probable surrogate for metabolic health that is more accurate than BMI,” Dr. Goldstein said.
“We have the equipment, it’s just a matter of updating the software,” he said.
Dr. Goldstein said he had no relevant disclosures.
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