A hereditary bleeding disorder resulting from a premature stop codon in thrombomodulin (p.Cys537Stop).

In this study, we describe a novel thrombomodulin (TM) mutation (c.1611C>A) that codes for a change from cysteine 537 to a premature stop codon (p.Cys537Stop). Three members of a family with a history of posttraumatic bleeding were identified to be heterozygous for this TM mutation. All coagulation screening tests, coagulation factor assays, and platelet function test results were within normal limits. However, the endogenous thrombin potential was markedly reduced at low-tissue factor concentration, and failure to correct with normal plasma indicated the presence of a coagulation inhibitor. Plasma TM levels were highly elevated (433-845 ng/ml, normal range 2-8 ng/ml, equating to 5 to 10 nM), and the addition of exogenous protein C further decreased thrombin generation. The mutation, p.Cys537Stop, results in a truncation within the carboxyl-terminal transmembrane helix. We predict that as a consequence of the truncation, the variant TM is shed from the endothelial surface into the blood plasma. This would promote systemic protein C activation and early cessation of thrombin generation within a developing hemostatic clot, thereby explaining the phenotype of posttraumatic bleeding observed within this family.

Point-of-care assessment of hypothermia and protamine-induced platelet dysfunction with multiple electrode aggregometry (Multiplate®) in patients undergoing cardiopulmonary bypass.

BACKGROUND: Coagulopathy is common after cardiopulmonary bypass (CPB), and platelet dysfunction is frequently considered to be a major contributor to excessive bleeding. Exposure to hypothermia may exacerbate the platelet function defect. We assessed platelet function during and after deep hypothermia with multiple electrode aggregometry (Multiplate(®); Verum Diagnostica GmbH, Munich, Germany). METHODS: Twenty adult patients undergoing pulmonary endarterectomy for chronic pulmonary hypertension were cooled on CPB to 20°C and deep hypothermic arrest was used to facilitate surgery. We analyzed platelet aggregation in whole blood samples at 12 measuring points during and after the procedure. Platelet aggregation was stimulated via the thrombin receptor (TRAPtest) at the patient's actual body temperature (AUC-CT) and after rewarming the samples to 37°C (AUC-37). In addition, we tested samples at 2 time points after 2 minutes of in vitro incubation with 20 µg protamine (0.067 µg/µL). Results are expressed as area under the aggregation curve (AUC). RESULTS: Cooling resulted in a marked decrease of platelet aggregation to a minimum AUC-CT of 20.5 (95% confidence interval [CI] 8.9-32.1) at 20°C body temperature. AUC-CT was significantly different from baseline (92.8, 95% CI 82.5-103.1) for temperatures of ≤28°C (P < 0.001), whereas the change in AUC-37 only became significant at the lowest body temperature (59.4, 95% CI 41.3-77.4). After rewarming to 36°C, AUC-CT and AUC-37 had recovered to 67.6 (95% CI 53.9-81.3) and 71.7 (95% CI 52.5-90.8), respectively. The mean AUC-CT was significantly lower than the mean AUC-37 from cooling at 28°C to warming at 24°C inclusive, and the relationship with temperature during cooling was significantly different between AUC-CT and AUC-37 (regression coefficients 4.7 [95% CI 4.2-5.2] vs 1.3 [95% CI 0.7-1.9]; P < 0.0001). After administration of protamine, mean aggregation decreased significantly for both measurements by 38.2 (95% CI -27.9 to -48.5; P < 0.001) and 44.5 (95% CI -58.5 to -30.5; P < 0.001), respectively. Similarly, adding protamine in vitro resulted in a decrease of mean aggregation by 35.1 (95% CI -71.0 to 0.8; P = 0.055) when measured after administration of heparin, and 56.5 (95% CI -94.5 to -18.5; P = 0.005) at the end of CPB. CONCLUSION: Platelet aggregation, assessed by multiple electrode aggregometry (Multiplate), was severely affected during deep, whole-body hypothermia. This effect was partially reversible after rewarming, and was distinct from a general decline of platelet aggregation during CPB. Protamine also caused a significant decrease in platelet aggregation in vivo and in vitro.

Critical factors contributing to the thromboelastography trace.

The thromboelastography trace provides a graphical and numerical representation of the viscoelastic changes associated with fibrin polymerization. When used with whole blood, the shape of this trace is a composite of the effects of white and red cell content and composition, platelet number and function, fibrinogen concentration, as well as coagulation protein function and balance. The trace is also influenced by pharmacological agents such as anticoagulants, antiplatelet therapy, and coagulation factor supplementation. As such the main role of this technology has been as a point-of-care device to guide transfusion of blood components. Recently the technology has moved from the cardiac and hepatic surgical settings, where most of the early work was focused, into other areas of hemostatic monitoring. New applications for pharmaceutical monitoring and patient screening are being explored. This review gives a broad overview of the applications of the technology. In particular it considers the factors that most influence the characteristics of the trace, be they preanalytical, analytical, or clinical.