Reference intervals for calcium, phosphate, and alkaline phosphatase as derived on the basis of multichannel-analyzer profiles.

In an attempt to demonstrate a rapid and economical approach to deriving reference intervals, we analyzed data on plasma calcium and phosphate from a multichannel analyzer for more than 20 000 subjects and data on alkaline phosphatase from more than 10 000 subjects. Subjects were selected by the criterion, that their results for constituents other than the one of interest were within current reference intervals. Thus we have been able to include older patients who have diseases that accompany old age, but that do not affect test results. The mean concentrations of calcium and phosphate decreased with increasing age in both sexes, except for an abrupt increase for women about the time of reaching menopause. Similarly, the mean alkaline phosphatase activity increased with age in both sexes, reflecting a skewed frequency distribution. Here also, there was an abrupt increase in the modal value for women near menopause.