Defining cut-off values for the diagnosis of osteoporosis in postmenopausal women by quantitative ultrasonography of the phalanx

Abstract

Aim. Quantitative ultrasound (QUS) of the phalanx is a non-invasive, inexpensive and portable method for bone assessment. We determined a cut off point for it in the diagnosis of osteoporosis.

Methods. In 180 postmenopausal women, dual-energy X-ray absorptiometry (DEXA) of the spine and femur and QUS of the phalanx were performed. Then, the optimum cut-off point for QUS was determined.

Results. Osteoporosis was found in 28.8% of women by DEXA (18.3% in L2–L4, 3.9–7.8% in different regions of the femur) and in 28.9% by QUS. Agreement of the methods (kappa value) was 0.317 for spine and 0.036–0.068 for femoral regions. Using receiver-operating characteristic (ROC) curves, we found T-score of −2.0 as the optimum cut-off point of QUS in diagnosing osteoporosis in the spine (sensitivity and specificity were 78.8% and 55.9%, respectively). We did not find a cut-off point for femoral regions because the 95% confidence interval of the area under the ROC curve contained the diagonal line (p = 0.150, 0.179 and 0.05 for femoral neck, trochanter and total femur, respectively). We defined −2.5 as the other T-score cut-off point under these different conditions; more specificity is needed.

Conclusion. Agreement was weak to moderate between the two methods. Thus QUS of the phalanx is not a good replacement for DEXA in defining osteoporosis, but it may be used as a screening method.

Keywords:

• Quantitative ultrasound
• dual-energy X-ray absorptiometry
• bone mineral density
• osteoporosis
• menopause
• cut-off