Background and Evaluation of Hypercoagulability

The Clotting Process

Abnormalities of laboratory hemostatic parameters, as well as clinical disorders related to bleeding and thrombosis, are common in patients with liver disease, especially those with cirrhosis or acute liver failure. The endothelial proteins von Willebrand factor (VWF) and thrombomodulin among others can also be used to define the status of clotting in patients with cirrhosis. The normal clotting process begins with spontaneous or iatrogenic tissue injury, including to the vascular endothelium, leading to the initiation and formation of the platelet plug. This platelet plug formation is specifically initiated by damage to the endothelium. This damage can also result from other types of physical trauma to the vessel, chronic overexposure to stress hormones or inflammatory mediators, or physical rupture of plaque, as in coronary artery disease. Endothelial damage exposes platelets to collagen, which in turn promotes platelet adherence and activation. Activated platelets secrete both adenosine diphosphate and thromboxane A2, which are synthesized via the arachidonic acid pathway. Adenosine diphosphate and thromboxane A2 both promote further platelet recruitment and aggregation, resulting in the formation of a platelet plug.

Indexed through the National Library of Medicine (PubMed/Medline), PubMed Central (PMC), and EMBASE.

Disclaimer

Funding for this clinical monograph has been provided by Dova Pharmaceuticals. Support of this monograph does not imply the supporter’s agreement with the views expressed herein. Every effort has been made to ensure that drug usage and other information are presented accurately; however, the ultimate responsibility rests with the prescribing physician. Gastro-Hep Communications, Inc., the supporter, and the participants shall not be held responsible for errors or for any consequences arising from the use of information contained herein. Readers are strongly urged to consult any relevant primary literature. No claims or endorsements are made for any drug or compound at present under clinical investigation.

©2021 Gastro-Hep Communications, Inc. 611 Broadway, Suite 605, New York, NY 10012. Printed in the USA. All rights reserved, including the right of reproduction, in whole or in part, in any form.

The clotting process is then propagated by the coagulation cascade and controlled and also terminated by antithrombotic control mechanisms. Endothelial damage exposes blood to subendothelial tissue factor, which is found in the extravascular tissues. Intravascular sources of tissue factor, including endothelial cells and monocytes, have also been identified. Tissue factor is also found on hepatocytes, but is usually hidden from the circulation (encrypted). Injury can cause de-encryption. The reason this is important is that intrasinusoidal coagulation is activated in liver injury, leading to microvascular thrombosis and a possible “second hit” in the presence of local ischemia. Sources of intravascular tissue factor (eg, endothelial cells, blood cells) are normally repressed; however, during an inflammatory state, such as sepsis, intravascular tissue factor production may increase. Exposure to tissue factor initiates activation of the extrinsic or tissue factor pathway, which in turn initiates thrombin generation. After the initial generation of a small amount of thrombin, the tissue factor pathway is rapidly inhibited by the activation of tissue factor pathway inhibitor. However, the thrombin that is generated is able to activate platelets to build more platelet surface through aggregation and to produce a surface that is conducive to procoagulant activity through the expression of phospholipids. In addition, the initial amount of thrombin activates factor XI in the intrinsic pathway. Activation of factor XI, along with the creation of a platelet procoagulant surface, amplifies the generation of thrombin via the intrinsic “tenase” and prothrombinase complexes (Figure 1).

Figure 1.

Endothelial damage: initiation of thrombin generation. FXI, factor XI.

Thrombin generation is the pivotal point of the coagulation process. The prothrombotic actions of thrombin include amplification of thrombin generation via factor XI and platelet activation, as well as clot formation via conversion of fibrinogen to fibrin and the activation of factor XIII, which is required for the crosslinking of fibrin. The interaction of platelets and thrombin generation results in the formation of the fibrin-platelet clot, a barrier that impedes blood loss. Ultimately, the clot may be removed by fibrinolysis.

Clotting in Patients With Liver Disease

Among patients with liver disease, the clotting process is impacted by several events. Chief among them is a deficiency in the synthesis of the factors necessary for the coagulation cascade. All coagulation factors (except VWF, factor VIII [partially synthesized in the liver], and calcium) are produced in the liver. Factors II, VII, IX, and X are dependent on vitamin K; thus, factor deficiency can be related to vitamin K deficiency, decreased synthetic function, or increased consumption. In patients with liver disease, decreased levels of vitamin K are common for 2 reasons: dietary deficiency and lack of absorption in those with cirrhosis. In addition, in cirrhosis or acute liver failure, there is a lack of functional interaction with vitamin K in the liver cell. Furthermore, on the procoagulant side, there is also decreased degradation of activated coagulation factors, decreased synthesis of anticoagulant factors such as protein S and protein C, as well as synthesis of abnormal coagulation factors (including abnormal fibrinogen). Table 1 lists other clotting alterations noted in patients with cirrhosis.

Table 1.

Clotting Alterations in Patients With Cirrhosis

Abnormality	Description
Platelet abnormalities	Decreased amount Splenic sequestration Decreased thrombopoietin levels Bone marrow suppression Autoantibody destruction Increased function (minor) New platelets: old platelets are selectively destroyed/sequestered in the spleen Poor function Uremia Changes to vessel wall phospholipid composition
Hyperfibrinolysis	Accelerated intravascular coagulation and fibrinolysis Resembles disseminated intravascular coagulation, except for markedly elevated factor VIII Parallels degree of liver dysfunction Mild systemic fibrinolysis is found in 30% to 45% of cirrhotic patients. Clinically evident fibrinolysis is seen in 5% to 10% of patients Ascites is associated with increased fibrinolytic activity

Interestingly, cirrhosis predisposes patients to venous thrombosis and potentially to venous thromboembolism. These clotting events, especially when they occur in the portosystemic circulation, are a serious clinical problem. Commonly encountered clinical scenarios include portal vein thrombosis, Budd-Chiari syndrome, deep venous thrombosis and pulmonary embolism, thrombotic diathesis leading to nodular regenerative hyperplasia, progression of cirrhosis with parenchymal extinction nodules, and hepatic artery and portal vein thrombosis after liver transplant.

Separately, acquired or inherited thrombophilias can manifest in the portal or hepatic veins and result in thrombotic liver disease. Such patients may require thoughtful anticoagulation management to treat blood clots, as well as thromboprophylaxis before and after procedures. The evaluation of acquired and inherited thrombophilia in patients with venous or arterial thrombosis and liver disease is important because these disorders impact the success of liver transplant and the patient’s prognosis.¹ Identification of a specific prothrombotic state may guide subsequent therapy, influence duration of therapeutic anticoagulation, and increase precautionary measures in the care of these patients.

Based on the patient’s clinical scenario, history, findings, signs, and symptoms, it may be necessary to test for the acquired or inherited thrombophilias listed in Table 2. A personal or family history of thromboembolic events is an important part of the evaluation, and may be present in patients without an identifiable inherited clotting disorder. A negative test evaluation does not preclude an unidentified inherited disorder. Screening for protein C, protein S, and antithrombin deficiencies in liver failure by direct blood levels is often futile or confusing because levels are often low due to the liver disease. Conversely, factor V Leiden and factor II gene tests are never false-positive.

Table 2.

Acquired or Inherited Thrombophilias

Disorder	Testing—NOT Perturbed by Abnormal Hemostatic Parameters or Anticoagulation	Testing—Perturbed by Abnormal Hemostatic Parameters or Anticoagulation
Factor V Leiden	Genetic testing	APC-resistance test
Prothrombin gene mutation	Genetic testing
Protein C deficiency		Protein C activity (low)
Protein S deficiency		Protein S activity (low)
ATIII deficiency		ATIII activity (low in liver disease and with heparin; can be elevated with warfarin)
Familial FVIII elevation		FVIII activity (elevated in liver disease and inflammation)
Hyperhomocysteinemia and homocystinuria (cystathionine beta synthase deficiency)	Serum homocysteine massively elevated (>100 µmol/L; often 200-400 µmol/L). Part of newborn screen in many states
Acquired Disorders
Antiphospholipid syndrome	Anti-cardiolipin antibodies, anti–β2-GPI-antibodies	DRVVT for lupus anticoagulant
Myeloproliferative neoplasm	JAK2 mutation (V617F and exon 12-15); CALR, MPL mutations
Paroxysmal nocturnal hemoglobinuria	Flow cytometry of peripheral blood or bone marrow for CD59 and CD55
Protein S deficiency in HIV-positive patients

APC, activated protein C; ATIII, antithrombin III; DRVVT, dilute Russell viper venom time; FVIII, factor VIII; GPI, glycosylphosphatidylinositol.

Portal vein thrombosis is the most common macro-thrombotic manifestation in patients with liver disease, occurring in 8% to 18% of patients with cirrhosis.^2,3 The risk for portal vein thrombosis is lower in patients with Child-Pugh A disease, increases with worsening liver dysfunction and decreased portal flow, and is increased in patients with liver disease due to nonalcoholic steatohepatitis who are undergoing liver transplant.^4-7 Deep venous thrombosis and pulmonary embolism are other forms of macrothrombotic complications, which have been reported in 5% of hospitalized patients with acute and chronic liver disease.⁸

Microthrombotic complications include intrahepatic microthrombi (“parenchymal extinction”) resulting in nodules,⁹ portopulmonary hypertension, and cirrhosis as an ischemic/reinjury process.

Coagulopathy of Liver Disease

The coagulopathy of liver disease refers to the prolonged plasma coagulation (measured as prolonged prothrombin time [PT]), coupled with low blood platelet counts, that is observed in patients with cirrhosis.^3,10 The understanding of coagulopathy in patients with liver disease has greatly evolved over the past 2 decades.¹¹

Originally, it was thought that patients with advanced liver disease with prolonged clotting times had “auto-anticoagulation.” However, more recent data have contradicted this theory, and have recognized an increased prevalence of thrombotic complications in patients with liver disease and cirrhosis. Thus, there is no “auto-anticoagulation” in cirrhosis, and instead there is a concept of “rebalanced hemostasis.” This terminology reflects a careful balance in which the hemostatic imbalance caused by a decrease in the hepatic synthesis of procoagulants is “rebalanced” by a concomitant decrease in the hepatic synthesis of anticoagulant proteins (Table 3).¹²

Table 3.

The Concept of “Rebalanced Hemostasis” in Chronic Liver Disease

Changes That Impair	Changes That Promote
Hemostasis	Hemostasis
Thrombocytopenia	↑Levels of von Willebrand factor
Impaired platelet function	↓Levels of ADAMTS-13
↑Production of nitric oxide and prostacyclin	↑Level of factor VIII
↓Levels of factors II, V, VII, IX, X, XI	↓Levels of protein C, protein S, antithrombin, α2-macroglobulin, and heparin cofactor II
Vitamin K deficiency	↓Levels of plasminogen
Dysfibrinogenemia
↓ α2-antiplasmin, factor
XIII, and TAFI
↑t-PA levels

ADAMTS-13, a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13; TAFI, thrombin-activatable fibrinolysis inhibitor; t-PA, tissue plasminogen activator.

However, major events such as gastrointestinal bleeding, infection, and renal failure can upset the delicately rebalanced hemostasis of cirrhosis.

Evaluation for Hypercoagulability

Evaluation for hypercoagulability (Table 4) should be considered in appropriate patients, especially those with family history, unprovoked/unexplained venous or arterial thromboembolism, and venous thromboembolism in an unusual location (ie, splanchnic or hepatic vein thrombosis, dural venous sinus thrombosis).

Table 4.

Evaluation for Hypercoagulability

Tier 1 Can be useful in clinical circumstances (special caution with recent thrombotic event or use of anticoagulation)

Factor V Leiden mutation Prothrombin gene mutation Antithrombin activity Protein C level, activity Protein S level, activity Lupus anticoagulant assay (eg, DRVVT, PTT-LA) Antiphospholipid (β2 glycoprotein, cardiolipin) antibodies, IgG, and IgM

Tier 2 Useful in certain circumstances; order in consultation with hematologist

Factor VIII level (cirrhotic patients have elevated levels, confounding interpretation) JAK2 V617F mutation testing with reflex to exon 12-15,CALR, MPL (consider with Budd-Chiari syndrome, polycythemia, normal platelet count despite portal hypertension, splenomegaly out of proportion to degree of cirrhosis) PNH flow cytometry for CD59 and CD55 (very rare; consider with pancytopenia, hemoglobinuria, iron deficiency)

DRVVT, dilute Russell viper venom time; Ig, immunoglobulin; PNH, paroxysmal nocturnal hemoglobinuria; PTT-LA, partial thromboplastin time–lupus anticoagulant.

Thromboelastography (TEG) and Rotational Thromboelastometry (ROTEM)

The PT test was originally designed for the management of patients receiving warfarin and is the foundation for evaluating blood clotting and dysfunction in vitamin K–dependent coagulation factors among patients taking warfarin. This measurement is now expressed as an international normalized ratio (INR) and used broadly in assessing patients’ coagulation status in many clinical settings. PT and the INR reflect some of the coagulopathy associated with synthetic dysfunction in patients with end-stage liver disease. INR has been validated as a prognostic marker for liver disease mortality (as a component of the Model for End-Stage Liver Disease [MELD] score),¹³ but not for bleeding risk. There can be wide interlaboratory variation in INR among patients with liver disease due to many confounding factors.¹⁴ Importantly, routine diagnostic tests, such as the PT/INR and the platelet count, do not adequately reflect the hemostatic status in patients with liver disease.

Bleeding episodes frequently occur in patients with liver disease and may be related to dysregulated hemostasis. However, bleeding episodes cannot be predicted by routine diagnostic tests, such as the PT/INR. Poor synthetic liver function and vascular endothelial dysfunction result in altered plasma levels of coagulation proteins, anticoagulation proteins, and factors involved in fibrinolysis, which confound bleeding risk assessment. Thus, an evaluation based on the INR or activated partial thrombo-plastic time (aPTT) is sensitive only to the levels of coagulation proteins and therefore not suitable to determine the overall hemostatic balance that helps define bleeding or thrombotic risk in patients with liver disease. aPTT has little use in the evaluation of patients with acute and chronic liver disease. Likewise, the level of predisposition to bleeding in liver disease due to thrombocytopenia—frequently caused by splenic pooling and/or reduced production of thrombopoietin—remains unclear.

Instead, thromboelastography (TEG) and a similar technique termed rotational thromboelastometry (ROTEM) are considered the most accurate tests to evaluate hypercoagulable, hypocoagulable, and rebalanced coagulation status and to help guide selection of anticoagulation therapy and indicate whether anticoagulation is even needed. The TEG and ROTEM analyzers measure both the kinetic and physical properties of clot formation. The kinetic properties include the time to initial fibrin formation and the rate of fibrin-clot buildup. The physical properties include clot quality or strength, which is dependent on platelet function, and clot stability, which is dependent on the extent of clot lysis. Table 5 provides a comparison of standard hemostatic laboratory tests with TEG/ROTEM parameters among healthy individuals and those with varying degrees of liver injury.^15,16

Table 5.

Comparison of Standard Hemostatic Laboratory Tests and TEG/ROTEM Parameters in Healthy Individuals and in Patients With Liver Disease

Parameter	Normal Range	ALI/ALF (N=51)	Cirrhosis (N=273)	Cirrhosis INR ≥1.5 (N=48)
Standard hemostatic laboratory tests
INR	0.9-1.1	3.4±1.7	1.3±0.3c	1.7±0.4c
Fibrinogen (mg/dL)	200-450	195±84	263±108b	179±89
Platelets (× 109/L)	172-440	186±95	112±79c	84±46c
TEG parametersd
Reaction time (min)	2.5-7.5	4.7±1.9	4.4±1.2	4.2±1.5
Kinetic time (min)	0.8-2.8	1.7 [0.8-20.0]	2.2 [0.8-16.6]	2.8 [1.2-16.6]b
α -angle (degrees)	55.2-78.4	63.7±12.2	62.6±9.3	58.1±10.8a
Maximum amplitude (mm)	50.6-69.4	55.0±10.9	51.5±10.4a	45.0±9.9d
Lysis-30 (%)	0.0-7.5	0.0 [0.0-2.1]	0.5 [0.0-5.2]d	0.25 [0.0-3.2]a

ALF, acute liver failure; ALI, acute liver injury; INR, international normalized ratio; ROTEM, rotational thromboelastometry; TEG, thromboelastography.

Patients with cirrhosis and an INR of 1.5 or greater were selected from the overall cirrhosis cohort. Normal range is for the local laboratory. Values are given as mean±standard deviation or median [range].

^aP <.05.

^bP <.001.

^cP <.0001. All comparisons are vs ALI/ALF.

^dTEG was performed on a Thrombelastograph Haemostasis Analyzer 5000 (Haemonetics Corp., Haemoscope Division). Clotting was initiated at 37°C by the addition of kaolin to 0.34 mL of recalcified blood.

Adapted from Stravitz RT. Gastroenterol Hepatol (N Y). 2012;8(8):513-52015 and Hugenholtz GCG et al. Res Pract Thromb Haemost. 2017;1(2):275-285.¹⁶

A standard TEG/ROTEM records 5 parameters.¹⁵ The variables measured by TEG and ROTEM are shown in Table 6.¹⁷ The reaction (r)-time (in minutes) shows the time of clot latency from the beginning of the clotting reaction to the initial formation of fibrin. The r-time loosely corresponds to INR and aPTT. The kinetic (k)-time (in minutes) is defined as the time required for the initial fibrin formation to reach a specific clot firmness. The α-angle (in degrees) represents the kinetics of clot formation and reflects the rate of fibrin formation and crosslinking. The maximum amplitude (MA, in mm) corresponds to the maximum clot strength and is also primarily dependent on the platelet count and function of platelets and the concentration of fibrinogen. Clot lysis at 30 minutes (Lysis-30; in percent) shows the clot dissolution within 30 minutes of reaching maximum amplitude, corresponding to fibrinolysis. ROTEM is shown in Figure 2. Viscoelastic measurement of clot formation in whole blood is shown in Figure 3. Figure 4 illustrates the parameters of a temogram using the terminology for TEG. Figure 5 provides a comparison of the terminology used in TEG and ROTEM.¹⁸

Table 6.

Variables Measured by TEG and ROTEM

Variable	TEG	ROTEM
Measurement period	-	Reaction time
Time from start to when waveform	R	Clotting time
reaches 2 mm above baseline
The time from 2 mm above baseline to 20 mm above baseline	K	Clot formation time
Alpha angle [°]	Slope between R and K	Angle of tangent at 2 mm amplitude
Maximum angle	-	CRF
Maximum strength	Maximal amplitude	Maximal clot firmness
Time to maximum strength	-	Maximal clot firmness–t
Amplitude at a specific time	A30, A60	A5, A10
Clot elasticity	G	Maximum clot elasticity
Maximum lysis	-	CLF
Clot lysis at a specific time (minutes)	CL30, CL60	LY30, LY45, LY60
Time to lysis	2 mm from maximal amplitude	CLT (10% difference from maximal clot firmness)

CLF, maximum lysis; CLT, clot lysis time; CRF, clot formation rate; K, clot kinetics, measuring time taken for a certain level of clot strength to be reached; R, measure of coagulation time from start to initial fibrin formation; ROTEM, rotational thromboelastometry; TEG, thromboelastography.

Adapted from Thromboelastography [TEG] & Rotational Thromboelastometry [ROTEM]. Practical-Haemostasis.com. https://www.practical-haemostasis.com/Miscellaneous/Global%20Assays/teg_rotem.html. Updated January 5, 2021. Accessed January 12, 2021.¹⁷

Figure 2.

Rotational thromboelastometry: clot formation in whole blood. Courtesy: R. Todd Stravitz, MD.

Figure 3.

Viscoelastic measurement of clot formation in whole blood. ROTEM, rotational thromboelastometry; TEG, thromboelastography. Courtesy: R. Todd Stravitz, MD.

Figure 4.

The parameters of a temogram using the terminology for TEG. R, measure of coagulation time from start to initial fibrin formation. Alpha angle, the angle between the midline and a line tangential to the developing “body” of the TEG trace. Represents clot kinetics of clot buildup and crosslinking. MA, maximum amplitude is the maximum width of the “body” of the TEG trace. Represents ultimate clot strength.

Figure 5.

A comparison of the terminology used in ROTEM (A) and TEG (B). The depictions demonstrate clot initiation, propagation, stabilization, and lysis. Adapted from Whiting D and DiNardo JA. Am J Hematol. 2014;89(2):228-232.¹⁸

Increasing evidence suggests that the net effect of a decrease in procoagulant and anticoagulant clotting factors in liver disease provides a relative rebalance of hemostasis. Prolonged PT (INR) and aPTT only crudely reflect the procoagulant pathway and are therefore not predictive of bleeding or thrombosis. In addition, the thrombocytopenia of liver disease does not reliably predict the risk of periprocedural or spontaneous bleeding events. This may be the case partly because liver disease platelets pooled by the spleen are systemically available, and may function well due to increased levels of VWF. We suggest that, instead of using PT and aPTT to assess coagulation status among patients with cirrhosis, those medical centers with TEG devices available should begin using TEG/ROTEM, complemented by measurement of fibrinogen levels and platelet count.

Acknowledgment

Dr Gish would like to acknowledge Timothy Halterman, MD, for reviewing this article.