Standardization of definition and management for bleeding disorder of unknown cause: communication from the SSC of the ISTH

In many patients referred with significant bleeding phenotype, laboratory testing fails to define any hemostatic abnormalities. Clinical practice with respect to diagnosis and management of this patient cohort poses significant clinical challenges. We recommend that bleeding history in these patients should be objectively assessed using the International Society on Thrombosis and Haemostasis (ISTH) bleeding assessment tool. Patients with increased bleeding assessment tool scores should progress to hemostasis laboratory testing. To diagnose bleeding disorder of unknown cause (BDUC), normal complete blood count, prothrombin time, activated partial thromboplastin time, thrombin time, von Willebrand factor antigen, von Willebrand factor function, coagulation factors VIII, IX, and XI, and platelet light transmission aggregometry should be the minimum laboratory assessment. In some laboratories, additional specialized hemostasis testing may be performed to identify other rare causes of bleeding. We recommend that patients with a significant bleeding phenotype but normal laboratory investigations should be registered with a diagnosis of BDUC in preference to other terminology. Global hemostatic tests and markers of fibrinolysis demonstrate variable abnormalities, and their clinical significance remains uncertain. Targeted genomic sequencing examining candidate hemostatic genes has a low diagnostic yield. Underlying BDUC should be considered in patients with heavy menstrual bleeding since delays in diagnosis often extend to many years and negatively impact quality of life. Treatment options for BDUC patients include tranexamic acid, desmopressin, and platelet transfusions.

Correlation between plasma clot properties, thrombin generation and whole blood fibrinolytic assays in patients presenting with STEMI

Background

Impaired endogenous fibrinolysis is a novel risk factor for recurrent adverse cardiovascular events in acute coronary syndrome (ACS) patients. This is independent of conventional cardiovascular risk factors and unaffected by dual antiplatelet therapy (DAPT). The mechanism underlying impaired endogenous fibrinolysis in ACS patients is currently unclear.

Aim

To identify the relationship between whole blood fibrinolysis, plasma fibrinolysis and thrombin generation in samples from STEMI patients.

Methods

In a large, prospective, observational study of 500 patients presenting with ST-segment elevation myocardial infarction (STEMI), blood samples were taken on arrival, after DAPT loading, and before administration of heparin or PPCI. Non-anticoagulated venous whole blood was analysed using the point-of-care Global Thrombosis Test, which assesses the time taken for occlusive thrombus formation under high shear (occlusion time, OT) and time required for spontaneous restart of flow as a measure of endogenous fibrinolysis (lysis time, LT). Patients were divided into 4 groups based on quartiles (Q) of whole blood LT (Q1: LT<1500s, Q2:1501–3000s, Q3:3001–4500s, Q4:>4500s). Plasma samples (20 per quartile) were examined in a thrombin generation assay using 1pM tissue factor to initiate and using a turbidity assay to determine the plasma clot lysis time (CLT).

Results

Clinical characteristics of patients were similar in the four groups. The whole blood LT in the 4 groups were Q1: 1194 (1125–1329) s, Q2: 1859 (1634–2157) s, Q3: 3638 (3252–3962) s, Q4: 6000 (5523–6000) s. As LT increased, there was a trend towards longer plasma CLT (50% CLT Q2: 88.5 [73.5–102] vs. Q4: 100 [85–128.5] min, p=0.088). As a continuous variable, there was no significant relationship between whole blood LT and plasma CLT, or between endogenous thrombin potential (ETP) and either whole blood LT or plasma CLT. There was a significant negative correlation between OT and velocity index (r=−0.425, p=0.0138), ETP (r=−0.519, p=0.002), peak thrombin generation (r=−0.390, p=0.0247) and a positive correlation with lag-time (r=0.427, p=0.013). There was positive correlation between CLT and white cell count (WCC, r=0.388, p=0.026), C-reactive protein (CRP, r=0.477, p=0.005) and maximum absorbance (MA, r=0.530, p=0.002). MA correlated with WCC (r=0.436, p=0.011) and platelet count (r=0.357, p=0.042). There was a negative correlation between OT and WCC (r=−0.537, p=0.001) and CRP (r=−0.381, p=0.029).

Conclusion

In patients with STEMI, increased platelet reactivity (shorter OT) correlated with increased thrombin generation (higher ETP, peak thrombin generation, velocity index and reduced lag time), demonstrating the key role of thrombin in occlusive thrombus formation. Fibrinolysis in whole blood was poorly related to plasma CLT or thrombin generation, suggesting that cellular components such as platelets, erythrocytes and neutrophil extracellular traps may significantly influence endogenous fibrinolysis.

Funding Acknowledgement

Type of funding source: None

Localization and Identification of Thrombin and Plasminogen Activator Activities in Model Human Thrombi by in situ Zymography

Human thrombi vary in their susceptibility to lysis and this is clinically important. Several potential contributory factors were examined in this study by using model thrombi, created under flow; these provide a robust, reproducible and easily-manipulated system. Here we identify the plasminogen activators (PA) active in model thrombi of known age and define the cellular and plasma contribution to activity in different areas. The cell-rich head of model thrombi had strong thrombin and PA activity, with coagulant activity also at the tail. Thrombin activity decreased as model thrombi were aged. PA activity in the thrombus head also decreased on ageing of thrombi but activity emerged around the thrombi, including the tail. Activity in the head of fresh model thrombi was primarily due to uPA, with some contribution from tPA. Experiments with thrombi prepared from platelet-rich plasma and added leucocytes showed that uPA activity at the head of fresh thrombi was derived from PMN. Older thrombi had tPA activity around the tail of the thrombus; this activity occurred in the absence of cells. This study highlights the importance of PMN-derived uPA activity in the lysis of fresh thrombi, with activity originating in the leucocyte-rich head. It also shows that thrombi are dynamic structures in which fibrin can be repeatedly laid down and lysed, observations that are relevant to therapeutic lysis and potential rethrombosis.

Medicinal Kaolin in Food Poisoning

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