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