DXA More Accurate Than BMI to Measure Obesity


From the annual meeting of the American Association of Clinical Endocrinologists

Major Finding: BMI failed to detect obesity in 37% and falsely detected it in 5% in a study of 1,234 adults who had both BMI and DXA measurements.

Data Source: Medical chart review of private adult outpatients.

Disclosures: Study funded by the PATH Research Foundation NY. Dr. Braverman, who is director of PATH medical centers in New York and Philadelphia, said he had no other financial disclosures.

BOSTON — Dual x-ray absorptiometry was a more accurate predictor of obesity than was body mass index in a retrospective comparison of the two measures in 1,234 adults.

Despite its widespread use, BMI is not an accurate indicator of body fat. Direct measures of adiposity, such as those obtained by dual x-ray absorptiometry (DXA), are far more precise, Dr. Eric R. Braverman and his associates reported in a poster at the meeting.”

“We have a big problem with the BMI. You could retitle it the 'baloney mass index.' It's a mathematical equation. … The scientific standard is clearly subpar compared to our other endocrinology standards,” Dr. Braverman of the department of neurological surgery at Weill Cornell Medical College, New York, said at a press briefing.

Medical records of 1,234 private adult outpatients (490 men, 744 women) who had both BMI and DXA measurements during 2003-2009 were analyzed. They had a mean age of 51 years, a mean BMI of 26.2 kg/m

Using BMI, 249 (20%) were classified as obese. DXA measurement showed that of those 249, 95% (237) were obese and 5% (12) were nonobese on the basis of body fat percentage.

Using DXA, 689 (56%) were classified as obese. Of those 689, 34% (237) were obese and 66% (452) were not obese based on BMI.

Thus, 37% of patients were misclassified by BMI: 452 were found to be obese by DXA but nonobese by BMI and 12 were obese by BMI but not by DXA. The 66% of patients classified as obese by DXA but who were “missed” by BMI had lower muscle and lean body mass, Dr. Braverman and his associates noted.

The BMI measurement of obesity in this study was approximately identical to the national percentage of obesity, which is also determined by BMI. “However, we have shown that BMI is a highly insensitive measure, resulting in an underdiagnosis of obesity. If we can extrapolate from the rest of our data on the national scale, it is very likely that obesity is a much bigger epidemic than is currently acknowledged,” the investigators said in the poster.

Dr. Braverman, who is also director of the Place for Achieving Total Health (PATH) medical centers, New York and Philadelphia, said in an interview that he foresees DXA becoming a routine part of clinical practice in the future, to measure bone density as well as assess obesity. “In the 21st century, the physical is really quite outdated and almost no yield to silent disease that every endocrinologist works in. DXA and an efficiency system that can deliver it at $3 a test will make it simply a part of the physical.

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