A bone calcium index based on partial-body calcium measurements by in vivo activation analysis.

Measurements of partial-body calcium by in vivo neutron activation analysis have been carried out on normal and osteoporotic subjects. Based on measurements on 16 normal subjects (volunteers less than 55 years of age), a calcium index has been established that takes into account variation in skeletal frame size. On the basis of this index, all osteoporotic patients have bone mineral content less than any of the normal subjects. The normal calcium indices range from 0.9 to 1.2, and the osteoporotic indices ranged from 0.41 to 0.83. Thirteen of 22 volunteers over 55 years of age had calcium indices less than 0.9 in agreement with the expected loss of calcium with age. Measurements of total-body potassium were also made on these same subjects and the calcium/potassium ratios calculated. Although as groups the older volunteers and older osteoporotic subjects had mean calcium/potassium ratios similar to the mean for the normal subjects, the osteoporotic subjects under 55 years of age had a mean calcium/potassium ratio significantly lower, indicationg that for this latter group the loss in bone mineral was not associated with a corresponding loss in muscle mass.