IMPROVED PROTAMINE-SENSITIVE MEMBRANE-ELECTRODE FOR MONITORING HEPARIN CONCENTRATIONS IN WHOLE-BLOOD VIA PROTAMINE TITRATION

An improved protamine-sensitive electrode based on a polymeric membran e doped with the charged ion exchanger dinonylnaphthalenesulfonate (DN NS) is used for monitoring heparin concentrations in whole blood. The electrode exhibits significant nonequilibrium potentiometric response to polycationic protamine over the concentration range of 0.5-20 mg/L in undiluted whole-blood samples. The sensor can serve as a simple end point detector for the determination of heparin via potentiometric ti trations with protamine. Whole-blood heparin concentrations determined by the electrode method (n greater than or equal to 157) correlate we ll with other protamine titration-based methods, including the commerc ial Hepcon HMS assay (r = 0.934) and a previously reported potentiomet ric heparin sensor-based method (r = 0.973). Reasonable correlation wa s also found with a commercial chromogenic anti-Xa heparin assay (r = 0.891) with corresponding plasma samples and appropriate correction fo r whole-blood hematocrit levels. Whereas a significant positive bias ( 0.62 kU/L; P <0.001) is observed between the anti-Xa assay and the pro tamine sensor methods, insignificant bias is observed between the prot amine sensor and the Hepcon HMS tests (0.08 kU/L; P = 0.02). The possi bility of fully automating these titrations offers a potentially simpl e, inexpensive, and accurate method for monitoring heparin concentrati ons in whole blood.