Direct measurement of unfractionated heparin using a biochemical assay

A number of investigations have noted that functional biological assays for heparin are not always reliable and may not reflect the actual biochemical level of heparin in patients receiving anticoagulant therapy. This creates the possibility that patients receiving anticoagulant treatment may have a n excess or deficiency of circulating levels of heparin. To address this pr oblem, we have developed a direct biochemical measurement of heparin. The h eparin assay uses fluorophore assisted carbohydrate electrophoresis (FACE) to directly measure the predominate disaccharide of unfractionated heparin. In this study, unfractionated heparin was measured in vitro throughout a w ide range of heparin concentrations in plasma. Seven in vivo pharmacokineti c studies in five normal subjects given 3,000 USP units of unfractionated h eparin intravenously showed a three-phase elimination process with higher p eak plasma levels and shorter elimination times than predicted from previou s studies. At these doses, heparin is largely eliminated intact through uri nary excretion. Body weight has a significant effect on heparin kinetics. W hen we compared the direct biochemical assay with two biological clotting a ssays, we found the latter can overestimate biochemical heparin concentrati ons. The FACE assay, due to its sensitivity, is also able to measure circul ating levels of endogenous heparin in plasma and urine. Direct heparin meas urement using the FACE technique is practical and useful for studies of the correlation of biochemical and biological activities.