Two measures of fracture risk – bone mineral density T score and FRAX score – are clinically useful in patients with type 2 diabetes, even though they tend to underestimate the increased fracture risk in this patient population, according to the results of a large study reported in the June 1 issue of JAMA.
But to be more accurate for older adults with diabetes, these treatment and diagnostic algorithms should undergo "refinements," said Ann V. Schwartz, Ph.D., of the department of epidemiology and biostatistics, University of California, San Francisco, and her associates (JAMA 2011;305:2184-92).
Type 2 diabetes is known to be associated with a higher bone mineral density (BMD) but, paradoxically, also with a higher risk of fracture. There has been concern that established methods for predicting fractures "may not perform adequately in patients with type 2 diabetes," the researchers said.
In what they described as the first study to prospectively examine the relationship between BMD and fractures in older adults with type 2 diabetes, Dr. Schwartz and her colleagues analyzed data from three large, prospective, observational studies that all used radiology reports and radiographs to confirm fracture diagnoses. The three studies also ascertained subjects’ diabetes status.
The Study of Osteoporotic Fractures (SOF) involved 7,926 white women at four U.S. clinical centers who underwent femoral neck-hip BMD measurement and were followed for the occurrence of fractures from 1988 through 2008. The Osteoporotic Fractures in Men Study (MrOS) involved 5,994 men at six U.S. clinical centers who underwent hip BMD measurement and were followed from 2000 through 2009. And the Health, Aging, and Body Composition (Health ABC) study involved 1,523 women and 1,442 men in their 70s, approximately half of whom were white and half black, who underwent hip BMD measurement and were followed from 1997 through 2007.
The FRAX (Fracture Risk Algorithm) scores were calculated for subjects in the SOF and MrOS studies by the World Health Organization (WHO) Collaborating Center for Metabolic Bone Disease, but not for subjects in the Health ABC study.
Dr. Schwartz and her associates found that both low BMD T score and high FRAX score were predictive of hip and nonspinal fracture in patients with diabetes. "However, for a given T score and age, those adults with diabetes had a higher risk of fracture than those without diabetes," they said.
For example, the risk of hip fracture in a woman with diabetes was equivalent to that of a nondiabetic woman with a T score of about 0.5 units lower.
The subjects with diabetes showed higher rates of fracture at any given FRAX score than did subjects who didn’t have diabetes, they noted.
"Interpretation of T score or FRAX score in an older patient with diabetes must take into account the higher fracture risk associated with diabetes. For example, ... a T score in a woman with diabetes is associated with hip fracture risk equivalent to a woman without diabetes with a T score of approximately 0.5 units lower," the investigators said.
"The FRAX score has been incorporated into U.S. guidelines for prevention and treatment of osteoporosis. The FRAX algorithm does not currently include type 2 diabetes as a risk factor for fracture, and our results indicate that use of the FRAX score in patients with diabetes will likely underestimate risk.
"An adjustment of this algorithm for type 2 diabetes seems justified, given the prevalence of diabetes among older adults," Dr. Schwartz and her associates said.
The reason diabetes raises fracture risk even as it appears to protect against loss of BMD is not understood. "Bone strength may be compromised through changes that are not captured with dual-energy x-ray absorptiometry, such as higher levels of advanced glycation end products in bone collagen. More frequent falls in older adults with diabetes could also increase fracture risk for a given BMD," they said.
This study was funded by an investigator-initiated grant from Amgen to Dr. Schwartz. She and her associates also reported receiving support from Novartis, Merck, Pfizer, Nycomed, and Roche.