Valor predictivo de la densitometría por ultrasonidos como método de cribado selectivo de la osteoporosis en atención primaria

Abstract

Objective. To determine the cut-off point of calcaneous quantitative ultrasound densitometry (QUS) as a selection method in primary care for referral of postmenopausal women for dual energy x-ray absorptiometry (DXA). Design. Diagnostic techniques trial. Setting. Four general practices in the Basque Country Autonomous Region, Spain. Participants. Randomly selected Caucasian women older than 45, chosen at random. A sample size of 146 women was used. Interventions. Calcaneous ultrasound bone mineral density (BMD) measurement, using Achilles Express® and DXA. Principal measurements. T-score BMD measurement on both devices. The sensitivity, specificity and positive predictive values of QUS and finally the ideal cut-off value were calculated. Results. The mean age of the sample was 58.2 (17.7) (range, 48-83 years old). The prevalence of women with osteoporosis, osteopaenia and normal DXA was 14.1%, 50.4% and 35.5%, respectively. The estimated sensitivity of QUS was 78.9% (56.7-91.5) and the specificity was 64.7% (55.6-72.8). The negative predictive value (NPV) was 94.9% (87.7-98.0) and the positive predictive value (PPV) was 26.8% (17.0-39.6). After the COR curve analysis, the ideal cut-off for QUS was determined as a T-score ≤ -2.0. Conclusions. Given its high NPV, QUS can be considered a useful device for screening before DXA. Its low PPV means it has to be combined with other complementary or substitutive selective screening methods, such as predictive rules, which should be evaluated in each specific use.