CHICAGO - If quantitative ultrasound were used as an initial screening exam among the patients with suspected osteoporosis referred to the Klinik Radiodiagnostik at the University of Vienna, it could have ruled out osteoporosis in 20% of patients, according to Dr. Stephan Grampp. This use of QUS will help patients avoid unnecessary follow-up exams with dual x-ray absorptiometry and the associated additional costs and radiation exposure, Grampp concluded.
But some listeners at the musculoskeletal scientific session at the RSNA Sunday morning questioned whether sending up to 80% of patients for additional testing would be cost-effective at all.
It is clear that quantitative ultrasound cannot be used as the sole test for diagnosis of osteoporosis, Grampp noted, citing his own earlier published study (AJR 1999 Aug; 173[2] 329-34) among others. However, the potential for QUS as a screening exam is still an open question.
QUS cut-off
To further explore QUS’ screening potential, Grampp and colleagues sought to determine a cut-off level for QUS of the calcaneus that would distinguish patients with normal bone density from those with osteoporosis.
DXA exams of the lumbar spine and femoral neck were used to identify osteoporotic patients from among 1357 people referred for evaluation in Grampp’s department. The World Health Organization’s definition of osteoporosis, T-score <-2.5 by DXA at the spine and femur, was used.
The researchers then identified the highest QUS T-scores among the osteoporotic patients. Among women with osteoporotic DXA values at the spine, the maximum QUS T-score was -1.0; among men it was -0.2. Among women with osteoporotic DXA values at the femur, the maximum QUS t-score was -0.6; among men it was 0.0.
These QUS T-scores could serve as cut-offs for ruling out osteoporosis in patients with higher measurements, Grampp said. However, he cautioned that the cut-offs were valid only for the Lunar Achilles system used for his heel measurements.
When questioned about the value of weeding out so few patients with an initial QUS exam, Grampp countered that his study looked at a comparatively afflicted population who had been referred because of suspected osteoporosis. "We were thinking of the general population," where QUS should screen out more patients, he stated.
Grampp was also asked about the fact that the QUS T-scores did not parallel the DXA T-scores as equipment manufacturers suggest they might. He said that well-known population variations could explain the low correlation.
By Tracie L. ThompsonAuntMinnie.com staff writer
November 29, 1999
