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 efficacy of screening with ultrasound densitometry of the calcaneus that can be achieved by adding direct-site mineral measurements of the lumbar spine and the femur when the ultrasound t-score is low.


METHODS
The author retrospectively analysed data from 2500 women for whom the results of both dual-energy x-ray absorptiometry of the lumbar spine and femur and ultrasonometry of the calcaneus were available. Various ultrasound t-score cut-off values (from 0 to -4.5) were tested to determine changes in sensitivity, specificity, false negatives, false positives and accuracy with and without adding direct-site measurements of the lumbar spine and the femur neck.


RESULTS
For this analysis, the addition of direct-site measurement data increases the specificity to 100% for all t-score cut-off values without affecting the sensitivity, thereby improving the accuracy; however, the number of false negatives remains unknown. The number of false negatives decreases as the cut-off value is increased, but with higher cut-off values, greater numbers of subjects would have to be recalled for direct-site measurements of the lumbar spine and the femoral neck, which would entail extra costs.


CONCLUSIONS
The accuracy of screening for low mineral content by calcaneal ultrasonometry is improved by recalling subjects for direct-site measurements if their ultrasound t-score falls below some arbitrary value. The cut-off value must be chosen to achieve a balance between the number of missed false negatives that are acceptable in the screening process and the number of subjects recalled for the direct-site study at additional cost. In remote areas, where dual-energy x-ray absorptiometry devices for performing the supplemental measurement are not usually available, the cost of transportation would be another factor.
Rosenthall
L
L
Department of Nuclear Medicine, Montreal General Hospital, Que.
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D002111:Calcaneus / Q000000981:diagnostic imaging*; D003720:Densitometry / Q000379:methods*; D005260:Female; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006801:Humans; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging*; D008403:Mass Screening / Q000379:methods*; D008875:Middle Aged; D010024:Osteoporosis / Q000517:prevention & control*; D011237:Predictive Value of Tests; D011859:Radiography; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014463:Ultrasonography