In vitro neutralization of heparin in plasma prior to the activated partial thromboplastin time test: an assessment of four heparin antagonists and two anion exchange resins.

This study was carried out to investigate the effects on the activated partial thromboplastin time test (APTT) when heparin in plasma was neutralized with protamine, Polybrene(R), poly-DL-lysine, or heparin neutralizing activity (HNA) extracted from platelets; or removed by means of the anion exchange resins TEAE cellulose or ECTEOLA cellulose. The effect on the APTT of adding the polycations protamine, Polybrene or poly-DL-lysine to citrated plasma was examined. The formation of heparin/polycation complexes was studied by means of their light scattering properties. The low yields of platelet HNA obtained excluded this from practical use as an in vitro heparin antagonist. ECTEOLA cellulose was unable to remove plasma heparin at levels as low as 1 U/ml by the technique employed. TEAE cellulose was able to efficiently remove at least 40 U of heparin from 1 ml of plasma but also caused a non-specific prolongation of the APTT. The polycations protamine, Polybrene, and poly-DL-lysine, possessed clot promoting activity at low concentrations and acted as anticoagulants in their own right at higher concentrations. At a plasma heparin concentration of 4 U/ml, protamine was the most efficient neutralizer of heparin, while at 10 U/ml, Polybrene was the most effective in this respect. It was concluded that care must be taken in the interpretation of the APTT after heparin neutralization or removal as heparin antagonist induced non-specific effects may be present.