Platelet Count Plays a Major Role in Regulating Fibrin Formation in Cirrhosis: Clinical Study of Whole Blood Coagulation

Abstract 2290

Recent studies document a paradoxical absence of bleeding in the setting of an abnormal PT and aPTT in cirrhosis. A new equilibrium is established between thrombin generation, fibrin formation and fibrinolysis in cirrhosis that confers protection from spontaneous bleeding and may pose a thrombotic risk. The purpose of this study was to evaluate the coagulation paradox in cirrhosis by using whole blood thromboelastometry. Citrate anticoagulated whole blood is added to a cuvette and coagulation is initiated by adding calcium with either a tissue factor (TF)-based reagent (ExTEM) or an intrinsic pathway activator reagent (InTEM). The transformation of blood into a gel is measured by a computer-based system (ROTEM Instrument) over 30 minutes. We collected samples after obtaining informed consent form patients with cirrhosis. Part of the sample was process for platelet-poor plasma and the PT and aPTT assays performed. The clotting time (CT) which is the time from the start of the assay until initiation of fibrin formation;the clot formation time (CFT), the time from initiation of clotting until a half maximum clot firmness were measured. In addition, maximal clot firmness (MCF) in the presence or absence of cytochalasin an inhibitor of platelet activation was also measured by Fib-TEM assay. The effect of platelet count on these measurements was also evaluated. A total of 54 patients were enrolled with a median MELD score of 16, median PT 19.5sec, median aPTT 46.5sec and median platelet count 77K/CUMM. Only 20% of the population had a platelet count greater than 100K/CUMM. The average CT and CFT measured by the ExTEM were 72sec (normal 38–79sec) and 178sec (normal 34–159sec) respectively. The InTEM assay average CT was 172sec (normal 100–240) and CFT 175sec (normal 20–110). Normal CT was seen in 73% of ExTEM measurements and normal CFT in 53%. CT in InTEM was normal in 93%. In contrast, the InTEM CFT was normal in only 20% of measurements. Changes in CFT, a measure of the rate of thrombin generation and fibrin formation, could be influenced by platelet count. Activated platelets must be able to bind and assemble enzyme complexes that promote thrombin formation. We measured ExTEM and InTEM assays with varying platelet concentrations in normal volunteers. The CFT prolonged in ExTEM assays at 75–90K/CUMM platelets and between 90–120K/CUMM with the InTEM assay for normal volunteers. The platelet count for cirrhotic patient samples that had an abnormal InTEM CFT had platelet count of 64K/CUMM while those with normal InTEM CFT had 136K/CUMM platelets. Cirrhosis patient samples with a normal CFT by ExTEM had an average platelet count of 95K/CUMM and those that had an abnormal CFT by ExTEM had a platelet count of 53K/CUMM. We then looked at whether fibrinogen levels as measured by a Fib TEM assay were normal in cirrhotic patients. We found that 84% had normal fibrinogen levels. When the MCF was abnormal 85% of the samples had platelet counts below 70K, while the others had a low fibrinogen level. Lastly we found 4 patients that had an elevated MCF and these patients had an elevated fibrinogen by FIB-TEM despite having a platelet counts less than 70 K. In conclusion, despite having abnormalities in PT and aPTT assays the ability to initiate and generate a fibrin gel in whole is not abnormal in many cirrhotic patients. If there is a defect in whole blood testing it is more readily detected by the INTEM assay a measure of the intrinsic pathway. The majority of the abnormalities in thrombin formation and generation of maximum fibrin clot are dependent on platelet number. Some patients with elevated fibrinogen levels can compensate for a reduced platelet number. These studies support recent data that suggest platelet count <70K increase the risk of bleeding after invasive procedures in cirrhosis. Future studies will examine whether whole blood coagulation assays can be used to identify cirrhotic patients at risk for bleeding and will require prospective randomized clinical studies. The coagulation paradox in cirrhosis requires evaluation of new assays to define hemorrhagic and thrombotic risk.