Quantitative ultrasound or clinical risk factors--which best identifies women at risk of osteoporosis?

Dual energy X-ray absorptiometry (DXA) is the current technique of choice to assess risk of future fracture and to diagnose osteoporosis as defined by bone mineral density (BMD). Guidelines for bone densitometry referral have been published listing clinical risk factors that might be considered grounds for assessment. However, these factors are known to be poorly predictive of subsequent BMD measurement and, accordingly, new inexpensive methods of selecting subjects for assessment should be sought. Quantitative ultrasound (QUS) of bone may be such a technique. Women (n = 250) considered by their general practitioners to be at risk of osteoporosis and who had been referred for DXA measurements of the spine and hip were recruited into the study. All underwent a QUS scan of the heel using a McCue CUBA Clinical machine, which measures broadband ultrasound attenuation (BUA) and velocity of sound (VOS), a clinical risk factor questionnaire, and spine and hip BMD measurement by a Norland XR-26 bone densitometer. Patients were categorized according to published diagnostic criteria for BMD, and these were also applied to the QUS parameters. Risk factors were arbitrarily categorized into "low", "medium" and "high" risk groups. Kappa scores were calculated to analyse the agreement between different techniques. Receiver operator characteristic (ROC) analyses were undertaken to demonstrate the technique with the best sensitivity and specificity for the detection of low BMD at the spine and hip. Analysis of the bone mass data demonstrated only moderate agreement (kappa 0.33) between femoral neck and spine BMD with femoral neck BMD and BUA showing a very similar level of agreement (kappa 0.31). ROC analysis demonstrated that VOS followed by BUA was the best predictor of low BMD, with risk factors alone being significantly poorer; QUS parameters are better predictors than clinical risk factors for women with low BMD and could be used effectively at the primary care level to indicate those who should be considered for full osteoporosis assessment. However, further study into the cost effectiveness of this approach is required.