Facilitated determination of ionized calcium.
Using a calcium-containing heparin preparation for anticoagulation, we determined [Ca2+], the mean concentration of ionized calcium, in whole blood of 120 healthy blood-donors to be 1.23 (SD 0.04) mmol/L. Similarly, for 50 intensive-care patients selected without conscious bias, the correlation between [Ca2+] in serum (mean 1.15, SD 0.10 mmol/L) and in whole-blood samples anticoagulated with the same heparin preparation (mean 1.15, SD 0.09 mmol/L) was very good (r = 0.95). Storing samples anaerobically on ice for as long as 2 h did not alter whole-blood [Ca2+]. On the other hand, various concentrations of calcium-free heparin preparations all induced a significant decrease in measured [Ca2+]. By using whole-blood samples, rather than plasma or serum, for [Ca2+] determination with a calcium-selective electrode, repetitive measurements can be made with simple handling procedures, facilitating rapid implementation of appropriate therapeutic measures for critically ill patients.
D000328:Adult; D002118:Calcium / Q000097:blood*; D004566:Electrodes; D005260:Female; D006493:Heparin; D006801:Humans; D008297:Male; D012016:Reference Values; D013048:Specimen Handling; D013696:Temperature
D006493:Heparin; D002118:Calcium