The Overall Haemostatic Potential (OHP) Assay Detects Abnormalities in Fibrinolytic Factors

No routine assays are available which quantify abnormalities in the fibrinolytic system. The Overall Haemostatic Potential (OHP) assay is a global assay of fibrin generation and fibrinolysis. Our aim in this study was to assess changes in fibrinolysis measured by the OHP assay in samples with variable levels of the different components of the fibrinolytic system: plasminogen, a2-antiplasmin, PAI-1 and TAFI. Plasmas deficient in these factors were obtained commercially. Samples were spiked with Lys-plasminogen, Glu-plasminogen, PAI-1, TAFI or pooled normal plasma to produce serial increases in these factors. Potato tuberose carboxypeptidase inhibitor (PTCI) was also used to inhibit TAFI in PNP and patient samples. OHP assays were performed utilizing either thrombin (0.03 IU/ml) or tissue factor (5 pM) to trigger fibrin generation, and rt-PA (350 ng/ml) to trigger fibrinolysis. Data analysis involved calculation of Spearman correlations for OHP assay parameters and concentrations of the various fibrinolytic factors tested. The OHP assay demonstrated markedly reduced fibrinolysis in plasminogen deficient plasmas, which normalised when plasminogen levels were increased to the normal range. At elevated Lys-plasminogen levels fibrin generation was impaired. Overall fibrinolytic potential was mildly increased in a2-antiplasmin deficiency. PAI-1 depleted plasma had mildly increased fibrinolysis compared with PNP but with addition of PAI-1, to concentrations of 300 ng/ml or higher, fibrinolysis was markedly impaired. TAFI deficient plasma had reduced fibrin generation but no change in fibrinolysis was seen in spiked samples, even with elevated TAFI levels. Representative hypofibrinolytic patient samples showed normalisation of fibrinolysis with TAFI inhibition by PTCI.

The OHP assay shows appropriate changes in OFP with variations in the concentrations of activators and inhibitors of the fibrinolytic system. The assay provides a simple means of quantifying overall fibrinolysis and is sensitive to abnormalities in individual components of the fibrinolytic system. It should be useful for investigating fibrinolytic abnormalities in patients, where no routine assay is currently available.