Recombinant platelet factor 4 reversal of heparin in human cardiopulmonary bypass blood

The ability of recombinant platelet factor 4, a protein of human origin with high heparin affinity, and the present clinical heparin reversal agent, protamine, to neutralize heparin in human whole blood was studied by means of three standard whole blood coagulation tests: whole blood clotting time, heparin assay, and activated clotting time. Ten subjects were chosen at random among patients undergoing cardiopulmonary bypass operations. Heparinized blood, free of protamine, was obtained from the bypass reservoir for testing. Whole blood aliquots, without reversal agents (controls) or with either protamine (10, 20, 30, or 40 micrograms/ml) or recombinant platelet factor 4 (10, 20, 40, or 80 micrograms/ml), were analyzed. The quantity of each agent required to reverse the ten samples, using 95% upper confidence bounds (t distribution) was determined for each method. Recombinant platelet factor 4 reversed heparin at 40 micrograms/ml and protamine at 20 micrograms/ml, suggesting a reversal ratio for recombinant platelet factor 4/protamine of 2:1 on a milligram basis. Further, currently available methods for testing coagulation should be reliable, without modification, to monitor the restoration of normal coagulation parameters with recombinant platelet factor 4 after cardiopulmonary bypass.