Comparison of bone density measurements from different skeletal sites.

Absorptiometric measurements from multiple sites in 212 consecutive patients were examined to determine the interrelationships among bone mineral content values obtained from the lumbar spine, hip, and forearm. Dual photon absorptiometry was used to examine the spine, femoral neck, Ward's triangle, and greater trochanter while the radius and ulna were studied with single photon absorptiometry. All studies were performed on the same day. Concurrent measurements were available for the spine and hip in 197 patients, for the spine and forearm in 151 patients, and at all three sites for 146 patients. Variable degrees of correlation were found among the mineral content values from the six sites, with r values ranging from 0.40 to 0.93. The femoral neck and Ward's triangle showed the highest degree of correlation (r = 0.93); the ulna and lumbar spine demonstrated the poorest correlation (r = 0.40). Relationships between distant anatomic sites exhibited a large amount of variability (large standard error of the estimate) even when highly correlated. Useful predictions of bone mineral content could be obtained only for sites in close proximity. These results suggest that bone mineral content determinations in the upper extremities by single photon absorptiometry may not be useful for predicting mineralization in clinically more significant areas such as the lumbar spine and hip.