Objective: We aimed to evaluate the chemical effect of heparin on ionized calcium (iCa). In this multi-step experimental study, we analyzed serum samples with Nova CCX blood gas analyzer.

Materials and Methods: In the first two steps, we calculated the percent changes of iCa in samples with decreased volumes, suctioned into the 1, 2, 5 and 10 ml syringes washed with liquid sodium heparin and into evacuated tubes, blood gas syringes, electrolyte balanced blood gas syringes with dry lithium heparin. In the last two steps, we determined a dose-reponse relation via calculating percent changes of iCa in serum pool samples containing 2500, 1250, 625, 313, 156, 78, 39, 20, 10, 5, 2, 1 IU/ml of heparin and effects of cations on dose-response relation by adding potassium (K) and magnesium (Mg) at 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 mM concentrations.

Results: Statistical differences in percent changes of ionized calcium were obtained between groups of samples of 10, 5, 2, 1, 0.5 ml volumes with syringes washed with liquid heparin and groups of samples of 2, 1, 0.5 ml volumes with containers containing dry heparin (p<0.05). A negative hyperbolic dose-response (heparin Ð percent changes in iCa) curve and a negative sigmodal log dose-responce curves were concluded. The log dose - reponse curve was shifted to left with adding of K of 10 mM, and the curve slope increased with adding of Mg of 10 mM.

Conclusion: Owing to the results of this preliminary study, we think that in vitro dose - response relation of heparin and percent changes in iCa will help us to find a solution for the chemical interference of heparin on electrolyte measurements in blood gas samples.