Identifying Fracture Risk in Postmenopausal Women

To the Editor: Dr Siris and colleagues¹ found that many asymptomatic postmenopausal women have previously undetected low bone mineral density (BMD). They also confirmed that peripheral bone densitometry, categorized according to T scores, is predictive of subsequent fracture risk in this population.

In this study, and often in clinical practice, the diagnostic threshold of a T score of −2.5 (BMD of 2.5 SDs below the peak adult value) is used. However, Siris et al found that the proportion of women with BMDs below this value varies dramatically by device, from 3.4% with heel ultrasound to 13.5% with finger dual-energy x-ray absorptiometry (DXA). When adjusted for age, weight, and other confounding factors, there was more than a 6-fold difference in the proportion below the threshold. Other studies have shown similar variations in the apparent prevalence of osteoporosis, as well as risk of fractures, when different devices are used with T-score thresholds.^{2 - 3}

The lack of comparability across peripheral devices represents an important barrier to the use of peripheral densitometry in clinical practice and is one reason that central (ie, hip and spine) DXA is recommended by the National Osteoporosis Foundation and the International Society for Clinical Densitometry as the definitive diagnostic tools.³ Furthermore, the central DXA has been shown to be more precise and predictive of hip fracture than peripheral densitometry or ultrasonography.⁴

While peripheral densitometry may be useful as a general risk assessment tool for patients and their physicians, central DXA of the hip and spine should be performed as the definitive diagnostic tool and used in treatment decision making. Diagnostic categories derived from T scores on peripheral devices are misleading and should not be relied on for treatment decisions.