This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. AbstractNumerous methods for evaluation of global fibrinolytic activity in whole blood or plasma have been proposed, with the majority based on tissue-type plasminogen activator (t-PA) addition to initiate fibrinolysis. We propose that such an approach is useful to reveal hypofibrinolysis, but t-PA concentrations should be kept to a minimum. In this paper, we describe a low-concentration t-PA plasma turbidity assay to evaluate several congenital factor deficiencies, including plasminogen activator inhibitor-1 (PAI-1) and plasminogen deficiency, as well as hemophilia A and B. In addition, we demonstrate a threshold dependency on endogenous PAI-1 levels. To assess endogenous hyperfibrinolysis, we suggest that assays that avoid t-PA addition are preferable, with assays based on euglobulin fractionation remaining a viable choice.We describe a euglobulin fraction clot lysis time (ECLT) assay with spectrophotometric readout and other modifications, and evaluate it as a tool to measure hyperfibrinolysis in inherited clotting factor deficiency states. We demonstrate that the ECLT is predominantly driven by residual amounts of PAI-1, t-PA, and α 2 -antiplasmin.These assays should be further evaluated for the detection of hypo-or hyperfibrinolysis in acquired thrombotic or hemorrhagic disorders. K E Y W O R D Seuglobulin clot lysis time, fibrinolysis, hemophilia, plasminogen, plasminogen activator inhibitor 1 Essentials• Clot lysis of the euglobulin fraction of plasma reliably assesses endogenous hyperfibrinolysis.• A modified version of the euglobulin clot lysis time (ECLT) is described herein.• This version of ECLT is sensitive to low plasminogen activator inhibitor-1 and high tissue-type plasminogen activator (t-PA) levels.• Turbidimetric assays of clot lysis using low amounts of t-PA are sensitive to hypofibrinolysis.

Introduction Deficiencies of plasminogen and plasminogen activator inhibitor type 1 (PAI‐1) are rare disorders of fibrinolysis. Current laboratory assays for analysis of activity of plasminogen and PAI‐1 do not provide an accurate correlation with clinical phenotype. Methods The Nijmegen Hemostasis Assay (NHA) was used to simultaneously measure thrombin and plasmin generation in 5 patients with plasminogen deficiency (PLGD) and 10 patients with complete PAI‐1 deficiency. Parameters analysed included: lag time ratio, thrombin peak time ratio, thrombin peak height, thrombin potential (AUC), fibrin lysis time, plasmin peak height and plasmin potential. Parameters were expressed as a percentage compared to a reference value of 53 healthy normal controls. Results Patients with PLGD demonstrated a short lag time and thrombin peak time, with normal thrombin peak height but an increased AUC. Plasmin generation was able to be detected in only one (23% plasminogen activity) of the five PLGD patients. All ten PAI‐1 deficient patients demonstrated a short lag and thrombin peak time, low thrombin peak height with normal AUC. Plasmin generation revealed an increased plasmin peak and plasmin potential; interestingly, there was a large variation between individual patients despite all patients having the same homozygous defect. Conclusion Patients with either PLGD or PAI‐1 deficiency show distinct abnormalities in plasmin and thrombin generation in the NHA. The differences observed in the propagation phase of thrombin generation may be explained by plasmin generation. These results suggest that disorders of fibrinolysis also influence coagulation and a global assay measuring both activities may better correlate with clinical outcome.