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PubMed This is a summary of 21 peer-reviewed journal articles Updated
Hematology · Budd-Chiari Syndrome

Causes and Clues: Why Do Blockages Form?

At a Glance

Budd-Chiari syndrome is usually linked to a tendency to form blood clots, often from an underlying bone-marrow blood disorder. Doctors also look for inherited or acquired clotting conditions, hormone exposure, tumors, cysts, and infections.

Understanding why Budd-Chiari Syndrome (BCS) happened to you is a critical part of your care. In many cases, BCS is not a random event; it is the result of one or more underlying conditions that make your blood “sticky” or more prone to forming clots [1][2]. Identifying these triggers helps your hematologist and hepatologist decide how to treat the current obstruction and how to prevent future ones.

The Role of Clonal Blood Disorders (MPNs)

The most frequently identified underlying causes of Budd-Chiari Syndrome are Myeloproliferative Neoplasms (MPNs) [3]. MPNs are chronic, clonal disorders of the bone marrow that can alter blood cells and increase thrombosis risk through multiple complex mechanisms—not just by “thickening” the blood [1].

  • The JAK2 Mutation: A specific genetic marker called the JAK2 V617F mutation is strongly associated with MPN-related BCS [4][3]. Your doctors will test your blood for this mutation, as well as others like CALR and MPL.
  • Hidden Disease: It is important to know that in BCS, your standard blood counts (like red cells or platelets) might look completely normal even if you have an MPN. This is because the congested liver or an enlarged spleen can “hide” or trap these extra cells, or because bleeding has lowered the counts [5].
  • Because a negative JAK2 blood test does not entirely rule out an MPN, your hematologist will individualize your workup, which may ultimately include a bone marrow biopsy [6].

Other Clotting Triggers

Many other conditions can make you prothrombotic (prone to clotting). Often, a patient has more than one risk factor present at the same time [7].

Inherited Conditions

These are genetic traits that affect how your blood clots:

  • Factor V Leiden or Prothrombin Gene Mutation: Genetic changes that can increase clotting risk [2][7].
  • Protein C, Protein S, or Antithrombin Deficiency: These proteins are natural “brakes” on the clotting system [8]. Note: Testing for these proteins can be distorted by acute clotting, liver disease itself, or the blood thinners you are taking. Your hematologist will carefully time and interpret these tests.

Acquired Conditions and Contributors

  • Antiphospholipid Syndrome (APS): An autoimmune disorder where the body produces antibodies that attack its own tissues, leading to clots [7][9].
  • Paroxysmal Nocturnal Hemoglobinuria (PNH): A rare blood disease that can cause severe clots in the abdominal veins [10][9].
  • Hormonal Factors: Estrogen exposure—such as from oral contraceptives, hormone replacement therapy, or pregnancy—can be an independent contributor to clot formation, or it may act as an additional trigger in someone who already has an underlying thrombophilia [11][12]. Any decisions about birth control or pregnancy should be carefully discussed with your care team.

Secondary Causes: When Something Presses on the Vein

In some cases, the blockage isn’t a clot that started inside the vein. Instead, something outside the vein is compressing it or invading it [13]. This is called Secondary Budd-Chiari Syndrome. Causes can include:

  • Tumors: Cancers of the liver (hepatocellular carcinoma) or kidneys can sometimes compress or grow into the hepatic veins or the inferior vena cava [14][15].
  • Cysts or Infections: Large benign cysts or certain parasitic infections can put enough pressure on the veins to block blood flow [16][17].

What is Sinusoidal Obstruction Syndrome (SOS)?

Sometimes BCS is discussed alongside a condition called Sinusoidal Obstruction Syndrome (formerly Veno-Occlusive Disease). While both cause liver congestion, they affect different anatomy and have different causes [18]:

  • Budd-Chiari Syndrome involves the outflow tract from the small hepatic veins up to the large inferior vena cava [19].
  • SOS is a toxic injury and obliteration of the microscopic sinusoids and terminal venules deep inside the liver tissue [1][18].

SOS is almost always triggered by specific exposures, such as high-dose chemotherapy, radiation, or stem cell transplants [20][21]. Because imaging cannot always definitively separate small-vessel BCS from SOS, specialists use your clinical history, laboratory findings, imaging, and occasionally a liver biopsy to make the correct diagnosis.

Common questions in this guide

What are the most common causes of Budd-Chiari syndrome?
The most frequently identified causes are myeloproliferative neoplasms, which are bone-marrow disorders that can make clots more likely. Other causes include inherited or acquired clotting disorders, estrogen exposure, and blockage from tumors, cysts, or infections. More than one risk factor may be present.
Can I have an MPN even if my blood counts and JAK2 test are normal?
Yes. Liver congestion, an enlarged spleen, or bleeding can make blood counts look normal, and a negative JAK2 V617F test does not completely rule out a myeloproliferative neoplasm. A hematologist may consider CALR or MPL testing and, when appropriate, a bone marrow biopsy.
Which blood-clotting conditions might doctors check for?
Testing may include Factor V Leiden, a prothrombin gene mutation, low protein C, protein S, or antithrombin, as well as antiphospholipid syndrome and paroxysmal nocturnal hemoglobinuria. Acute clotting, liver disease, and anticoagulants can alter some results, so a hematologist must choose the timing and interpret the findings.
Can hormones or pregnancy contribute to hepatic vein thrombosis?
Yes. Estrogen exposure from oral contraceptives, hormone replacement therapy, or pregnancy can increase clotting risk or add to another clotting tendency. Discuss contraception, hormone therapy, or pregnancy planning with your care team.
How can doctors tell whether the blockage is a clot or something pressing on the vein?
Primary Budd-Chiari syndrome is caused by blockage within the hepatic veins or nearby outflow tract, usually from clotting. Secondary Budd-Chiari syndrome occurs when a tumor, cyst, infection, or another outside process compresses or grows into a vein, and imaging helps evaluate the difference.
How is sinusoidal obstruction syndrome different from Budd-Chiari syndrome?
Budd-Chiari syndrome affects the liver’s larger outflow veins, while sinusoidal obstruction syndrome damages tiny channels and terminal veins within liver tissue. Sinusoidal obstruction syndrome is commonly linked to high-dose chemotherapy, radiation, or stem cell transplantation; doctors use the medical history, laboratory findings, imaging, and sometimes a liver biopsy to distinguish it.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Have I been tested for the JAK2 V617F mutation, as well as CALR or MPL mutations, as markers of myeloproliferative neoplasms (MPNs)?
  2. 2.Since blood counts can sometimes look normal in Budd-Chiari even when an MPN is present, should I have a bone marrow biopsy?
  3. 3.Which specific inherited and acquired blood-clotting disorders have you screened me for, taking into account that my liver function and anticoagulants might affect the results?
  4. 4.Is my blockage caused by a blood clot (primary BCS) or by something outside the vein pressing on it (secondary BCS)?
  5. 5.Do my imaging and clinical history clearly distinguish my condition from Sinusoidal Obstruction Syndrome (SOS)?

Questions For You

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References

References (21)
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    Review article: a multidisciplinary approach to the diagnosis and management of Budd-Chiari syndrome.

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    The epidemiology of Budd-Chiari syndrome in France.

    Ollivier-Hourmand I, Allaire M, Goutte N, et al.

    Digestive and liver disease : official journal of the Italian Society of Gastroenterology and the Italian Association for the Study of the Liver 2018; (50(9)):931-937 doi:10.1016/j.dld.2018.04.004.

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    Splanchnic vein thrombosis and myeloproliferative neoplasms: molecular-driven diagnosis and long-term treatment.

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This page explains possible causes and diagnostic tests for Budd-Chiari syndrome for informational purposes only and does not constitute medical advice. Your hematologist and hepatologist should interpret your results and guide decisions about clotting tests, blood thinners, hormones, pregnancy, or procedures.

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