Diagnosis of thrombophilia/prothrombotic conditions in patients with liver disease

Watch a video presentation of this article

Answer questions and earn CME

Introduction

Thromboses of splanchnic veins are encountered increasingly by clinicians, either as a complication of chronic liver disease (typically cirrhosis with or without hepatocellular carcinoma) or as the first presentation of a primary form of vascular liver disease, such as noncirrhotic portal vein thrombosis (PVT) or Budd‐Chiari syndrome (BCS), in a previously healthy person. PVT forms part of the spectrum of idiopathic noncirrhotic portal hypertension (INCPH).

Hypercoagulability and Thrombophilia

Hypercoagulability is defined as a procoagulant imbalance due to increased plasma levels of coagulation factors not compensated for by naturally occurring anticoagulants. It occurs in physiologic states, such as pregnancy and the puerperium, and in acquired conditions, such as the postoperative state, prolonged immobilization, estrogen use, inflammatory/infectious diseases, antiphospholipid syndrome, and cancer. Hypercoagulability is also encountered in inherited conditions due to mutations in the genes encoding factor V and factor II or, more rarely, in deficiencies of the naturally occurring anticoagulants protein C, protein S, and antithrombin. Thrombophilia, the tendency to venous thromboembolism due to hypercoagulability, is a relevant risk factor for splanchnic vein thrombosis in patients with primary vascular disorders of the liver.1 Laboratory screening for thrombophilia should include a functional test for activated protein C resistance, genotyping of the factor V gene to search for the G1691A mutation (FV Leiden) and the factor II gene for the G20210A mutation, measurement of antithrombin, protein C and protein S, factor VIII, basal plasma homocysteine levels, and antiphospholipid antibody assays.2 High levels of factors IX and XI, although more likely acquired than inherited, have also been identified as markers of thrombophilia, but their inclusion in a thrombophilia screening is not currently recommended.

A list of laboratory tools to assess for the most frequent inherited or acquired prothrombotic condition in liver disease is reported in Table 1.

Table 1.

Most Frequent Prothrombotic Conditions Detected in Hepatology: Relative Prevalence in PVT, BCS, INCPH, and Liver Cirrhosis and Diagnostic Tests

Prothrombotic Risk Factor	Prevalencea				Diagnosis
	PVT	BCS	INCPH	Liver Cirrhosis
MPN	30%‐40%	40%‐50%	10%	NA	Hypersplenism and hemodilution due to portal hypertension mask abnormal blood cell count; detection of V617F JAK2‐mutation; in patients testing negative, consider bone marrow biopsy; other JAK2 (exon 12) or MPL mutations rarely found
Factor V Leiden	6%‐32%	6%‐32%	0%	5%‐13%	Functional test: resistance to activated protein C; genetic confirmatory test: FV G1691A mutation
Factor II gene mutation	14%‐40%	5%‐7%	3%	9%‐35%	G20210A mutation
Primary protein C deficiency	0%‐26%	10%‐30%	3%	NA	Decreased protein C activity levels interpretable only in presence of normal levels of coagulation factors; a positive first‐degree relative is necessary to confirm inherited deficiency
Primary protein S deficiency	2%‐30%	7%‐20%	3%	NA	Decreased protein S levels interpretable only in presence of normal levels of coagulation factors; a positive first‐degree relative is necessary to confirm inherited deficiency
Primary antithrombin deficiency	0%‐26%	0%‐23%	0%	NA	Decreased protein antithrombin activity levels interpretable only in presence of normal levels of coagulation factors; a positive first‐degree relative is necessary to confirm inherited deficiency
Hyperhomocysteinemia	12%‐22%	37%	NA	21%‐44%	Often difficult to establish; high serum levels prior to the thrombotic disease are necessary; C677T homozygous polymorphism and/or levels of vitamin B12 and folic acid may be useful
Recent oral contraceptives use	12%	6%‐60%	NA	NA	Medical history
Antiphospholipid syndrome	6%‐19%	4%‐25%	4%	5%‐44%	Anticardiolipin antibody at high levels or lupus anticoagulant, or anti‐beta2‐glycoprotein 1 antibodies
Paroxysmal nocturnal hemoglobinuria	0%‐2%	0%‐4%	NA	NA	Detection of CD55‐ and CD59‐deficient clone by flow cytometry

^aIncludes the minimum and maximum percentage described for noncirrhotic patients in refs. 2 and 5 and in refs. 6, 7, and 9 for cirrhotic patients.

Abbreviation: NA, not available.

Thrombophilia/Prothrombotic Conditions in Primary PVT and BCS

One or more prothrombotic disorders or an established risk factor for venous thrombosis can be found in the vast majority of patients with BCS or PVT. Philadelphia‐chromosome negative chronic myeloproliferative neoplasms (MPNs), account for about half of cases of BCS and 25‐30% of PVT not resulting from cancer or other obvious circumstantial risk factors. The search for the Janus kinase 2 (JAK2 V617F) mutation is positive in the majority of patients with an underlying MPN.3 This somatic point mutation confers constitutive kinase activity leading to enhanced hematopoiesis independent of growth factors. It is present in 95%‐97% of patients with polycythemia vera, up to 90% of those with unclassifiable MPN, and around 50% of patients with essential thrombocythemia and idiopathic myelofibrosis. However, because the absence of the JAK2 mutation does not exclude the presence of MPN and its presence does not define the phenotype, bone marrow biopsy is often needed to rule out or specifically define the type of MPN. Other MPN‐associated JAK2 mutations (in exon 12) and in the gene encoding the thrombopoietin receptor have been described, but very few patients with such mutations and primary splanchnic vein thrombosis have been reported.

Finally, other rare causes of thrombosis of the splanchnic veins should be considered. Among these, paroxysmal nocturnal hemoglobinuria should be assessed using flow cytometry, even in the absence of clinical signs of hemolysis, anemia or dark urine.

Thrombophilia in INCPH

The mechanistic role of thrombophilia in INCPH is less defined due to a lack of studies on this topic. In a small patient cohort, a 54% prevalence of prothrombotic disorders was found,4 but larger studies are needed to confirm these findings. Chronic abdominal infections are recognized as the main risk factor for INCPH in the East, while drugs, toxins, immunological or genetic disorders are more often the cause in the West, with thrombophilia as a facilitating factor.

Thrombophilia in Liver Cirrhosis

PVT occurs frequently in the course of cirrhosis, particularly in its advanced stage. It may occur because of slowing of portal flow and vessel wall damage. Hypercoagulability, the third component of the classical triad of pathogenic factors for venous thromboembolism, has been reported at an increased rate in some studies, but not in others. Causes include factor V Leiden and prothrombin gene mutation, hyperhomocysteinemia, protein C and protein S deficiencies, and elevated factor VIII.5, 6 An increased prevalence of antiphospholipid antibodies has also been reported, although its role remains controversial due to the inconsistency of the available studies.

Unfortunately, once an impairment of the liver synthetic function has ensued due to thrombosis of the main hepatic vessels, the causes and consequences are often indiscernable. Detecting a specific prothrombotic condition does not influence the medical treatment, which is the same whatever the cause. However, in accordance with international recommendations,2, 7 thrombophilic screening is often indicated, especially to justify lifelong anticoagulation. Well‐designed human studies are warranted for a more evidenced‐based approach.

The Confounding Effect of Liver Disease on Thrombophilia Screening

Inherited defects of the anticoagulant proteins antithrombin, protein C, and protein S are very rare, and in the context of an acquired liver disease, they should more often be regarded as acquired than inherited. Decreased levels of one of the coagulation inhibitors should be suspected to be inherited only when levels of other coagulation factors and inhibitors are normal or almost normal.8 Only in this unusual situation should a family study be performed to check for a hereditary etiology of these deficiencies. In a study of 65 patients with primary PVT assessed for thrombophilia, only four out of 18 patients with deficiency of one or more anticoagulant proteins had a hereditary deficiency confirmed.1

High levels of factor VIII, IX, and XI have been recognized recently as markers of prothrombotic risk. Increased plasma levels of factor VIII seem particularly associated with both cirrhotic and noncirrhotic PVT.9 Unfortunately, liver disease resulting from thrombosis of its main venous vessels confounds these findings, as factors IX and XI decrease in the setting of impaired liver synthesis, whereas factor VIII increases in this situation. Therefore, the role of these risk factors for venous thrombosis in primary vascular disorders of the liver is still questioned.

The diagnosis of the metabolic abnormality hyperhomocysteinemia also suffers similar limitations in patients with liver disease. After liver disease is established, assessing whether homocysteine plasma levels are markers of a risk factor for thrombosis or a consequence of the disease is difficult to discriminate. Vitamin supplementation (with folic acid, pyridoxine, and vitamin B12) is generally effective in reducing plasma homocysteine levels.

Finally, portal hypertension and the resulting hemodilution and hypersplenism mask the typical peripheral blood features of MPN. Hence, all patients with primary vascular disorder of the liver should be evaluated for MPN, regardless the peripheral blood cell counts, by testing for the JAK‐2 mutation.

Liver disease as a prothrombotic condition

Recently, the old belief of liver cirrhosis as the epitome of acquired hypocoagulability has been dismissed in favor of a new theory of a rebalanced hemostasis in cirrhosis, due to the parallel reduction of procoagulants and anticoagulants synthesized by the liver.10 Further refinements of such research now suggests a procoagulant imbalance in cirrhosis, mainly due to increased levels of factor VIII (one of the main triggers of thrombin generation) and low levels of protein C (one of the main inhibitors of thrombin generation and of activated factor VIII). This imbalance occurs even in the presence of a marked prolongation of the traditional coagulation tests PT and APTT that, due to their design, are much more sensitive to procoagulant than to anticoagulant factors. Indeed, more refined tests such as the thrombin generation test confirm that plasma from patients with cirrhosis is able to generate even greater amounts of thrombin than healthy subjects, provided that it is measured in the presence of thrombomodulin, the endothelial thrombin receptor that, in vivo, quenches thrombin generation by activating protein C. It has been shown that the addition of thrombomodulin is able to efficiently inhibit thrombin generation in normal plasma, but not in plasma from patients with cirrhosis, given the marked reduction of protein C in plasma from these subjects. Therefore, cirrhosis, particularly in its advanced stage, and regardless of the coexistence of markers of thrombophilia, is considered to be an acquired prothrombotic condition, thus clarifying the apparent paradox of an increased tendency to PVT (and probably of venous thromboembolism in general) in a disease previously supposed as the archetype of acquired hypocoagulability.

Abbreviations

BCS

Budd‐Chiari syndrome

INCPH

idiopathic noncirrhotic portal hypertension

JAK2

Janus kinase 2

MPN

myeloproliferative neoplasm

PVT

portal vein thrombosis.