A list of device-specific thresholds for the clinical interpretation of peripheral x-ray absorptiometry examinations

Abstract

The UK National Osteoporosis Society (NOS) has recently issued new guidelines on the use of peripheral x-ray absorptiometry (pDXA) devices in managing osteoporosis. The NOS guidelines recommend a triage approach in which patients' bone mineral density (BMD) measurements are interpreted using upper and lower thresholds specific to each type of pDXA device. The thresholds are defined so that patients with osteoporosis at the hip or spine are identified with 90% sensitivity and 90% specificity. Patients with a pDXA result below the lower threshold are likely to have osteoporosis at the hip or spine, patients with a result above the upper threshold are unlikely to have osteoporosis, while those between the two thresholds require a hip and spine BMD examination for a definitive diagnosis. This report presents data from a multicenter study to establish the triage thresholds for a range of pDXA devices in use in the UK. The subjects were white female patients aged 55-70 years who met the normal referral criteria for a BMD examination. For each device, at least 70 women with osteoporosis at the hip or spine and 70 women without osteoporosis were enrolled. All women had hip and spine BMD measurements using axial DXA systems that were interpreted using the National Health and Nutrition Examination Survey (NHANES) reference range for the hip and the manufacturers' reference ranges for the spine. Data are presented for five different devices: the Osteometer DTX-200 (forearm BMD), the Schick AccuDEXA (hand BMD), the GE Lunar PIXI (heel BMD), the Alara MetriScan (hand BMD), and the Demetech Calscan (heel BMD). The clinical measurements were supplemented by theoretical modeling to estimate the age dependence of the triage thresholds and the effect of the correlation coefficient between pDXA and axial BMD on the percentage of women referred for an axial BMD examination. In summary, this study provides thresholds for implementing the new NOS guidelines for managing osteoporosis using pDXA devices. The figures reported apply to postmenopausal white women aged 55-70 years who meet the conventional criteria for a BMD examination. The results confirm that the thresholds are specific to each type of pDXA device and that the NOS triage algorithm requires 40% of women to have an axial DXA examination.