A normal reference standard for radiocalcium turnover and excretion in humans

To overcome a lack of normal reference values for radiocalcium behavior in adult humans, a composite standard has been assembled from 23 studies performed in 6 laboratories. Both plasma calcium specific activity and isotope excretion values are presented at intervals from five- to three-hundred hours after isotope injection. The statistical grouping of plasma specific activity values at each time interval was relatively tight: the coefficient of variation approximated 20 per cent. A small correlation with body surface area was detected, and sample variances were somewhat smaller when the individual values were corrected for differences in area. No correlation between specific activity and either age or sex was observed. The data are presented solely to provide a preliminary numerical estimate of the normal range, and to offer a standard composite curve suitable for analysis by any of the several mathematical models describing calcium turnover.