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Specific heparin preparations interfere with the simultaneous measurement of ionized magnesium and ionized calcium
1Department of Laboratory Medicine, School of Medicine, University of Washington, USA.
Objective:
To determine whether heparin anticoagulants used for analysis of whole blood ionized calcium would influence the measurement of ionized magnesium.
Methods:
The effects of zinc heparin, lithium heparin, 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 magnesium and calcium concentrations were apparent with zinc heparin but not with lithium or electrolyte-balanced heparin. Ionized magnesium and calcium concentrations were more significantly influenced by volume-dependent changes in zinc heparin potency than with lithium or electrolyte-balanced heparin.
Conclusion:
Zinc heparin produces a significant positive bias in the simultaneous determination of ionized magnesium and ionized calcium concentrations.