The usefulness of dual energy X-ray and laser absorptiometry of the calcaneus versus dual energy X-ray absorptiometry of hip and spine in diagnosing manifest osteoporosis.

INTRODUCTION: Osteoporosis is a major health problem. Dual energy X-ray absorptiometry (DXA) of the hip and spine is the worldwide standard in diagnosing osteoporosis. Measurement of bone mineral density (BMD) with dual energy X-ray and laser absorptiometry of the calcaneus (Calscan) might be a good alternative. Advantages of the Calscan are that it is quick, widely available and manageable. In this study we compared BMD expressed in T-scores measured by DXA and Calscan. The aim of this study was to define threshold T-scores on the Calscan that could exclude or predict osteoporosis correctly in comparison with DXA.
MATERIALS AND METHODS: Patients > or =50 years attending our emergency department with a fracture were offered osteoporosis screening at our fracture and osteoporosis outpatient clinic (FO-Clinic) and enrolled in this study. BMD was measured at the hip and spine using DXA and at the calcaneus using Calscan. A T-score measured by DXA < or =-2 standard deviations (SD) below the reference population was defined as manifest osteoporosis and was the treatment threshold.
RESULTS: During a 10-month study period, 182 patients were screened with both devices. The mean DXA-T-score was -1.63 SD (range -4.9 to 2.1) and Calscan T-score -1.91 SD (range -5.3 to 1.4). There was a significant correlation between both devices (r = 0.47, P < 0.01). Using an upper threshold for the Calscan T-score of -1.3 SD, 47 patients could be classified as non-osteoporotic with 89.3% sensitivity (95% CI 80.0-95.3%). Using a lower threshold for the Calscan T-score of -2.9 SD, 34 patients could be classified by the Calscan as osteoporotic with 90.7% specificity (95% CI 83.5-95.4). The remaining 101 patients could only be correctly classified by DXA-T-scores.
CONCLUSION: Although DXA is the established modality worldwide in measuring BMD it is restricted to specialized centres. Peripheral bone densitometers like the Calscan are widely available. When BMD measurements with DXA were compared to Calscan measurements it was possible to correctly classify 81 of 182 patients based on the Calscan T-score. Of these 81 patients 34 could be classified as manifest osteoporotic and 47 as non-osteoporotic. Therefore the Calscan seems to be a promising technique which might be used as a screening device at a FO-Clinic, especially when DXA is not easily available.