Ionized Calcium: Its Significance and Clinical Usefulness*

NC 27514 M aintenance of normal blood levels of ionized calcium (Ca2 +) plays an important role in the m anagement of the critically ill patient. Therefore, Ca2+ should be collected properly and m easured reliably. The sound ana lytical performance of today’s Ca2+ analyzers using ion-selective electrode technology have made m easurem ents accurate and precise. The introduc tion of this technology allows rapid and direct analysis in whole blood or serum, resulting in an enhanced reporting tim e. Since the am ount of heparin in the syringe was shown to lower plasma ionized calcium con centration artifactually, samples for plasma Ca2+ determ ination should be anticoagulated with a m easured quantity of heparin. Ancillary factors in Ca2+ determ ination include effects of changes in sample pH, and situa tions where abnormal concentrations of calcium ligands are present. Many clinical situations require Ca2+ rather than total calcium m easurem ents. Liver transplantation, citrated blood transfusions, and neonatal hypocalce mia are examples of a few such circumstances where determ ination of Ca2 + may be more physiologically and clinically meaningful than total calcium