RADIOCALCIUM STUDIES OF BONE FORMATION RATE IN HUMAN METABOLIC BONE DISEASE*

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Abstract
Calcium45 tracer studies were performed in 12 adult human subjects with and without bone disease. The size of the misciblc calcium pool averaged slightly less than 100 mg. Ca/Kg. in all subjects, except for 2 patients with osteitis deformans in whom the pools were four times that size. A direct relationship between the size of the pool and the rate of bone formation was demonstrated, and attributed to the variable contribution of the mass of newly formed bone to the miscible calcium pool. Evidence is cited which indicates that this pool, despite its theoretical complexity, behaves as a single compartment. The turnover of this pool is shown to be greatly in excess of combined excretoiy loss and is therefore presumed to include loss of tracer into non-exchanging bone, in the process of bone formation. A method is described whereby this bone uptake may be estimated quantitatively. On the basis of a study in 1 normal adult in the present series, and of available studies in the current literature, the normal rate of bone formation is estimated to be approximately 9 mg. Ca/Kg./Day (mean for 10 subjects: 9.1 ± 3.9 S.D.). The rates of bone formation in 6 patients with osteoporosis uncomplicated by parathyroid disease were clearly within this tentatively normal range (9.4 ± 1.07). A much reduced rate of bone formation was found in 1 patient with uncomplicated hypoparathyroidism, a slightly elevated rate in a young male with familial hyperostosis, and greatly elevated rates in 2 patients with osteitis deformans. From the time of return of bone isotope into the pool, the biologic life of the shortest-lived species of bone was estimated, and measurement was made of the proportion of total bone formation represented by this recycling. In general, the time required for this earliest recycling seemed to vary inversely with the postulated turnover of bone.

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