SELECTIVE SUPPLEMENTATION OF CALCANEAL ULTRASOUND DENSITOMETRY WITH DUAL-ENERGY X-RAY ABSORPTIOMETRY OF THE SPINE AND FEMUR FOR POPULATION SCREENING

Objective: To determine the limitations on the improvements in the eff icacy of screening with ultrasound densitometry of the calcaneus that can be achieved by adding direct-site mineral measurements of the lumb ar spine and the femur when the ultrasound t-score is low. Subjects an d methods: The author retrospectively analysed data from 2500 women fo r whom the results of both dual-energy x-ray absorptiometry of the lum bar spine and femur and ultrasonometry of the calcaneus were available . Various ultrasound t-score cut-off values (from 0 to -4.5) were test ed to determine changes in sensitivity, specificity, false negatives, false positives and accuracy with and without adding direct-site measu rements of the lumbar spine and the femur neck. Results: For this anal ysis, the addition of direct-site measurement data increases the speci ficity to 100% for all t-score cut-off values without affecting the se nsitivity, thereby improving the accuracy; however, the number of fals e negatives remains unknown. The number of false negatives decreases a s the cut-off value is increased, but with higher cut-off values, grea ter numbers of subjects would have to be recalled for direct-site meas urements of the lumbar spine and the femoral neck, which would entail extra costs. Conclusions: The accuracy of screening for low mineral co ntent by calcaneal ultrasonometry is improved by recalling subjects fo r direct-site measurements if their ultrasound t-score falls below som e arbitrary value. The cut-off value must be chosen to achieve a balan ce between the number of missed false negatives that are acceptable in the screening process and the number of subjects recalled for the dir ect-site study at additional cost. In remote areas, where dual-energy x-ray absorptiometry devices for performing the supplemental measureme nt are not usually available, the cost of transportation would be anot her factor.