Specific heparin preparations interfere with the simultaneous measurement of ionized magnesium and ionized calcium.

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.