Comparison Between Measured and Calculated Free Calcium Values at Different Serum Albumin Concentrations

Free ionic calcium is the metabolically active component of total calcium (TCa) in blood. However, most laboratories report TCa levels that are dependent on serum albumin concentration. Hence, several formulae have evolved to calculate free calcium levels from TCa after adjustment for albumin. However, free calcium can directly be measured using direction selective electrodes rather than spectrophotometric methods used in autoanalyzers. This study compares the levels of free calcium obtained by measurement by direct ion selective electrode (ISE) and the one calculated as a function of TCa by formulae.