It may be appropriate to forgo dual-energy x-ray absorptiometry scanning and instead use body mass index to rule out osteoporosis in some obese patients, according to the findings of a large study presented by Dr. Thomas Nelson at the annual European Congress of Rheumatology.
Patients in the study with a BMI greater than 30 kg/m2, age younger than 70 years, and few clinical risk factors for osteoporosis had a low prevalence of osteoporosis, compared with the general population, said Dr. Nelson, a rheumatologist at the Royal Lancaster (England) Infirmary.
For example, after correction for risk factors including age, sex, index of deprivation, and a number of clinical risk factors (such as recurrent falls, smoking, rheumatoid arthritis, corticosteroid use, maternal hip fracture, excessive consumption of alcohol, fragility fractures, and secondary osteoporosis), a low BMI in 10,657 patients who were randomly assigned to a reference cohort was found to be an independent predictor of osteoporosis (area under the ROC curve, 0.72 for total hip osteoporosis and 0.67 for lumbar spine osteoporosis).
Use of a BMI threshold "of approximately 30 was found to give 93.6% sensitivity for hip osteoporosis and 90.8% for lumbar spine osteoporosis," Dr. Nelson said.
Thus, a hypothesis was formed that in obese patients, osteoporosis could be excluded without dual-energy x-ray absorptiometry (DXA), and only 6.4% of patients with hip osteoporosis – and 9.2% with lumbar spine osteoporosis – would be missed.
When the hypothesis was applied in a validation cohort of 5,329 patients, hip osteoporosis was seen in 2.7% of obese patients, and lumbar spine osteoporosis was observed in 7.2%, compared with 10.7% and 16.6%, respectively, in the entire cohort.
Among those younger than age 70 years, only 0.7% and 5.4% had hip and lumbar spine osteoporosis, respectively.
Patients in the study were scanned between June 2004 and August 2010. They were randomly assigned to the reference or validation cohorts. The cohorts did not differ in regard to age, sex, BMI, body fat percentage, deprivation, or number of clinical risk factors. About 23% of patients in both groups were obese.
Should the suggestion that DXA scanning is unnecessary for ruling out osteoporosis in obese patients be validated in other populations, the finding could help to minimize radiation exposure, improve convenience, and lower costs for many patients. However, it is plausible that a greater bone mineral density is required by obese patients, compared with nonobese patients, to avoid symptoms and fracture risk associated with osteoporosis, and further research is required in this area, he concluded.
Dr. Nelson had no disclosures to report.