Development of a rapid and sensitive chromogenic heparin assay for clinical use.

A new sensitive chromogenic heparin assay is developed, which is well suited for clinical use. For the assay two reaction mixtures are required which can be lyophilized and reconstituted on the day of use. These reagents are stable during at least 6 h. Only two time-dependent pipetting steps are necessary. Any compound that inactivates thrombin, or can potentiate thrombin inactivation by an inhibitor, can be measured with this assay, including standard heparin, low molecular weight heparins, hirudin, alpha-NAPAP, pentosan polysulphate and dermatan sulphate. It is shown that heparin can be measured accurately in whole blood and in plasma. By addition of dextran sulphate to one of the reagents a platelet factor 4-insensitive assay is developed, so heparin can be measured even in blood that is partially activated and thus contains platelet factor 4 which neutralizes heparin.