Standard Fracture Risk Tools Effective in Diabetes

Norra MacReady

May 31, 2011 — Bone mineral density (BMD) and fracture risk scores are reliable indicators of fracture risk in elderly people with type 2 diabetes mellitus (DM), a new study shows.

In an analysis of data from 3 prospective, observational studies of diabetic adults with a mean age of 73 to 74 years, lower femoral neck BMD T scores, and higher World Health Organization Fracture Risk Algorithm (FRAX) scores were associated with a higher risk for hip and nonspine fractures, investigators report in the June 1 issue of the Journal of the American Medical Association.

On average, BMD is higher in people with type 2 DM than people without diabetes, yet diabetic patients have a higher risk for fracture, the study authors explain. This paradox has elicited "concern that these established methods for predicting fractures may not perform adequately in patients with type 2 DM."

This analysis showed that despite higher BMD among patients with diabetes vs their nondiabetic counterparts, DM was associated with higher fracture risk at any given T or FRAX score, confirming both the paradox and the usefulness of standard predictors of fracture risk.

The study authors, led by Ann V. Schwartz, PhD, of the University of California, San Francisco, write that this is "the first study to our knowledge to prospectively examine the relationship between BMD and fracture in older adults with type 2 DM."

They examined data from the Study of Osteoporotic Fractures (SOF); the Osteoporotic Fractures in Men Study; and the Health, Aging, and Body Composition (Health ABC) Study. The 3 studies together included 9449 women and 7436 men, all community-dwelling adults in the United States. Of the participants, 770 women had type 2 DM, of whom 138 were taking insulin, and 1199 men had diabetes, of whom 134 were taking insulin.

At a mean follow-up period of 12.6 years, hip fractures occurred in 84 of the women with DM, and nonspine fractures occurred in 262 women. Among the men with DM, 32 experienced a hip fracture and 133, a nonspine fracture, for a mean follow-up period of 7.5 years.

Among the women with DM, for every 1-unit decrease in femoral neck BMD T score, the age-adjusted hazard ratio (HR) was 1.88 (95% confidence interval [CI], 1.43 - 2.48) for hip fractures and 1.52 (95% CI, 1.31 - 1.75) for nonspine fractures. For every 1-unit increase in FRAX hip fracture score, the HR for hip fractures was 1.05 (95% CI, 1.03 - 1.07). For every 1-unit increase in FRAX osteoporotic fracture score, the HR for nonspine fractures was 1.04 (95% CI, 1.02 - 1.05).

Among the men with DM, every 1-unit decrease in femoral neck T score was associated with an HR of 5.71 (95% CI, 3.42 - 9.53) for hip fractures and 2.17 (95% CI, 1.75 - 2.69) for nonspine fractures. Each 1-unit increase in FRAX hip fracture score was associated with an HR of 1.16 (95% CI, 1.07 - 1.27) for hip fractures, and every 1-unit increase in FRAX osteoporotic fracture scores was associated with an HR of 1.09 (95% CI, 1.04 - 1.14) for nonspine fractures.

"Our results indicate that femoral neck BMD and the FRAX score are as useful for the assessment of fracture risk in older adults with DM as in those without DM," the study authors write. However, they warn that any interpretation of the scores in this population must account for the higher fracture risk conferred by DM. They continue: "For example, using the mean differences in T scores between older adults with and without DM estimated from these cohorts, a T score in a woman with DM is associated with a hip fracture risk equivalent to a woman without DM with a T score of approximately 0.5 units lower (mean difference, 0.59; 95% CI, 0.31-0.87)."

Limitations of the study included lack of glucose measurements from the participants in the SOF, and no FRAX data from the Health ABC study. In none of the studies could the study authors confirm which patients had type 1 or type 2 DM, although "given the age range of these cohorts, it is likely that very few participants had type 1 DM." Also, the analyses did not include vertebral fractures and did not adjust for DM duration. Strengths of the study included the size and diversity of the population study, length of follow-up times, and adjudication of fracture outcomes.

"Femoral neck BMD T score and FRAX score are both associated with fracture risk in older adults with type 2 DM and appear to be useful for clinical evaluation of fracture risk," the study authors conclude. They also warn that, at any given T or FRAX score, fracture risk is higher in those with diabetes.

This study was funded by an investigator-initiated grant from Amgen. The Study of Osteoporotic Fractures is supported by the National Institutes of Health funding and the National Institute on Aging. The Osteoporotic Fractures in Men study is supported by National Institutes of Health funding and by a grant from the American Diabetes Association. The National Institute of Arthritis and Musculoskeletal and Skin Diseases, the National Institute on Aging, the National Center for Research Resources, and the National Institutes of Health Roadmap for Medical Research also provided grant support. The Health, Aging, and Body Composition study is supported by contracts from the National Institute on Aging; the National Institute of Nursing Research; and the Intramural Research Program of the National Institutes of Health, National Institute on Aging.

Dr. Schwartz has received an honorarium from Amgen. Some of the other study authors have disclosed various financial relationships with Amgen, Novartis, Merck, Pfizer, Nycomed, and/or Roche.

JAMA. 2011;305:2184-2192. Abstract