SPECIFIC HEPARIN PREPARATIONS INTERFERE WITH THE SIMULTANEOUS MEASUREMENT OF IONIZED MAGNESIUM AND IONIZED CALCIUM

Objective: To determine whether heparin anticoagulants used for analys is of whole blood ionized calcium would influence the measurement of i onized magnesium. Methods: The effects of zinc heparin, lithium hepari n, and electrolyte-balanced heparin on the simultaneous measurement of ionized magnesium and ionized calcium in serum were determined using ion selective electrodes. Results: Time-dependent biases in ionized ma gnesium and calcium concentrations were apparent with zinc heparin but not with lithium or electrolyte-balanced heparin. Ionized magnesium a nd calcium concentrations were more significantly influenced by volume -dependent changes in zinc heparin potency than with lithium or electr olyte-balanced heparin. Conclusion: Zinc heparin produces a significan t positive bias in the simultaneous determination of ionized magnesium and ionized calcium concentrations.