Development of an assay to quantify tranexamic acid levels in plasma

Dysregulations of blood clot breakdown (fibrinolysis) during vascular trauma can lead to excessive blood loss. Tranexamic acid (TXA) is an inhibitor of fibrinolysis that works by blocking the interaction between plasminogen and fibrin degradation products (FDPs) - a key step in fibrinolysis. Despite the widespread usage, there are no tests available in a clinical setting to monitor TXA levels. We developed a fluorescence resonance energy transfer (FRET)-based assay to quantify TXA concentrations in plasma by using 1) fluorescently labeled plasminogen, and 2) FDPs labeled with a fluorescence quencher. Once plasminogen binds the FDPs, the fluorescent signal is quenched. TXA causes plasminogen to dissociate from the FDPs, thus increasing fluorescence signal in a dose-dependent manner. The dose response was sensitive between 1 and 100 μM (0.16 and 15.7 mg/L). The intraassay and interassay variabilities were determined to be 5.7 % and 3.0 %, respectively. Limit of detection was estimated to be 0.28 μM (0.044 mg/L). When tested for measuring known levels of TXA added to plasma samples, the ratio between measured and expected TXA concentration was 1.0151. Our study demonstrates a novel assay that can rapidly quantify TXA concentrations in plasma samples, thus demonstrating its potential as an in-hospital tool.