Acquired haemophilia is a rare but serious bleeding disorder that can appear without warning in people who have never had bleeding problems before. Unlike the inherited form, this condition develops when the body’s immune system mistakenly creates antibodies that attack its own clotting factors, usually factor VIII. Understanding this disorder and recognising its signs early can be life-saving.

Understanding Acquired Haemophilia

Acquired haemophilia occurs when a person’s body develops autoantibodies, also called inhibitors (proteins produced by the immune system that block the function of clotting factors), against their own blood clotting factors. Most commonly, these antibodies target factor VIII (a protein essential for blood clotting), which is why the condition is often referred to as acquired haemophilia A. Unlike congenital or inherited haemophilia, which people are born with, acquired haemophilia develops later in life in individuals who previously had normal blood clotting.^[1]

The condition is fundamentally different from hereditary forms of haemophilia in several important ways. People with acquired haemophilia have no personal or family history of bleeding disorders, and their blood clotting tests would have been completely normal throughout their entire life until the condition developed. The immune system essentially loses tolerance to the body’s own clotting factors, though scientists are still working to understand exactly why this happens.^[3]

How Common Is Acquired Haemophilia

Acquired haemophilia is extremely rare, affecting approximately 1.5 people per million each year. This rarity means that many healthcare providers may never encounter a case during their entire career, which can make diagnosis challenging. The condition does not discriminate between men and women—both sexes are affected equally, unlike inherited haemophilia which primarily affects males.^[5][6]

The age distribution of acquired haemophilia shows a distinctive pattern with two peaks. The first peak occurs in younger adults, particularly women between 20 and 30 years old, and is often associated with pregnancy or the period shortly after giving birth. The second and larger peak appears in older adults between 68 and 80 years old, with no difference between males and females in this age group. This elderly population represents the majority of cases.^[7]

The mortality rate associated with acquired haemophilia is concerning, varying from 20% to 70% depending on different case series. Death is attributed to the underlying disorder in about half of cases, infections in 5-15% of cases, and major bleeding episodes in approximately 4% of cases. These statistics highlight the serious nature of this condition and the importance of prompt diagnosis and treatment.^[7]

What Causes Acquired Haemophilia

The exact reason why the immune system suddenly begins attacking the body’s own clotting factors remains unclear. Scientists believe there may be different mechanisms involved, including the presence of certain gene variations and the activation of specific immune cells called autoreactive CD4+ T lymphocytes. These immune cells, which normally help protect the body from infections, mistakenly identify clotting factors as foreign invaders that need to be destroyed.^[7]

In approximately half of all diagnosed cases, no specific cause or triggering factor can be identified. These cases are called idiopathic (having no known cause), meaning they occur spontaneously without any apparent reason. However, for the other half of cases, healthcare providers can identify an underlying condition or trigger that may have prompted the immune system to develop these harmful antibodies.^[1][5]

Risk Factors and Associated Conditions

Several conditions and circumstances can increase the risk of developing acquired haemophilia. Immunological or autoimmune disorders account for 17 to 18% of cases. These include systemic lupus erythematosus (a chronic disease where the immune system attacks various body tissues), rheumatoid arthritis (chronic inflammation of the joints), Sjögren syndrome, other connective tissue diseases, autoimmune thyroiditis, Grave disease, antiphospholipid syndrome, multiple sclerosis, temporal arteritis, myasthenia gravis, and Goodpasture syndrome.^[1]

Pregnancy and the postpartum period represent important risk factors, particularly for younger women. The condition can develop during pregnancy or within one year following childbirth, accounting for approximately 8.4% of total cases. Between 1% and 5% of all acquired haemophilia cases are diagnosed during pregnancy or the postpartum period. Women who develop this condition during or after pregnancy typically present with abnormal vaginal bleeding that doesn’t stop as expected.^[1][6][7]

Malignancies or cancers, both solid tumors and blood-related cancers, are associated with acquired haemophilia. Elderly patients, who form the majority of cases, often have multiple other health conditions and may be taking various medications including antiplatelet agents and anticoagulants, which can complicate the clinical picture and influence bleeding risk.^[6][7]

Certain medications have also been linked to the development of acquired haemophilia, though specific drugs are not always identified. Additionally, the condition can emerge in elderly people without any identifiable risk factors whatsoever, appearing completely out of the blue.^[7]

Recognising the Symptoms

The clinical presentation of acquired haemophilia varies dramatically from person to person. Some individuals experience life-threatening bleeding episodes, while others have only mild bleeding or, surprisingly, no bleeding symptoms at all. This variability makes the condition particularly challenging to recognise and diagnose. Most patients present with bleeding symptoms, but the severity can range across the entire spectrum.^[4][6]

The pattern of bleeding in acquired haemophilia is notably different from that seen in inherited haemophilia. Rather than bleeding into joints, which is characteristic of congenital haemophilia, people with acquired haemophilia typically develop large haematomas (collections of blood outside blood vessels), extensive bruising under the skin (called ecchymosis), and bleeding from mucous membranes. Spontaneous haemarthroses (bleeding into joints) are actually unusual in acquired haemophilia, unlike in the inherited form.^[6][7]

Common bleeding manifestations include bleeding into the skin, which appears as large purple or blue areas; bleeding into muscles and soft tissues; and bleeding from mucous membranes such as nosebleeds, bleeding from the gums, gastrointestinal bleeding, and blood in the urine. In some cases, bleeding first becomes apparent after a surgical procedure, though most bleeding episodes occur spontaneously without any obvious trigger or injury.^[7]

Life-threatening bleeds can occur and often involve the colon or small intestine. Bleeding into the head and brain can cause long-term problems including seizures and paralysis. The most dangerous period is typically during the initial several weeks after the condition develops, but life-threatening bleeding can happen at any point during the disease course if appropriate treatment is not started promptly.^[1][4]

Because patients with acquired haemophilia are often elderly with other health conditions and may be taking medications that affect bleeding, such as antiplatelet agents or anticoagulants, the overall clinical picture can be complex and requires individualised assessment and care.^[6]

Preventing Acquired Haemophilia

Unfortunately, there are no known preventive measures for acquired haemophilia because the condition develops spontaneously and the exact triggers for why the immune system begins producing autoantibodies against clotting factors remain unclear. Since approximately half of all cases are idiopathic with no identifiable cause, prevention strategies cannot be developed. For cases associated with underlying conditions, managing those conditions appropriately may theoretically help, though this has not been proven to prevent acquired haemophilia.

However, once someone has been diagnosed with acquired haemophilia, preventing bleeding episodes becomes crucial. Until the inhibitors are eliminated through treatment, individuals should avoid any activities that carry a significant risk of trauma or injury. Even minor invasive procedures such as dental work or injections should be postponed if possible, or carefully planned with appropriate preventive measures in place.^[11]

People diagnosed with acquired haemophilia need to be extremely cautious about physical activities that might trigger bleeding in soft tissues. Any bump, fall, or minor injury that a person without the condition wouldn’t think twice about could potentially lead to significant internal bleeding in someone with acquired haemophilia. This level of caution must be maintained until treatment successfully eradicates the antibodies and normal clotting function is restored.^[11]

How the Body Changes: Pathophysiology

In acquired haemophilia, the fundamental problem lies in the immune system’s production of autoantibodies that specifically target and neutralise coagulation factor VIII. These autoantibodies are typically detected using specialised laboratory tests called the Bethesda assay or its Nijmegen modification, which measure how strongly the antibodies block factor VIII activity.^[6]

When these antibodies bind to factor VIII, they prevent it from participating in the normal blood clotting cascade. The coagulation cascade (a series of chemical reactions involving various clotting factors that work together to form a blood clot) cannot function properly without adequate factor VIII activity. The antibodies work in a time and temperature-dependent manner, meaning their inhibitory effect increases with longer exposure and at body temperature.^[7]

The antibodies essentially act as blockers, physically interfering with factor VIII molecules and preventing them from doing their job. Even though the body continues to produce factor VIII, the presence of these neutralising antibodies means that much of this factor VIII becomes non-functional. The severity of bleeding doesn’t always correlate directly with the level of factor VIII activity or the titre (strength) of the inhibitor, making the condition somewhat unpredictable.^[4]

Laboratory testing typically shows a prolonged activated partial thromboplastin time or aPTT (a test that measures how long it takes for blood to clot) due to the factor VIII deficiency. The prothrombin time, bleeding time, and platelet count usually remain normal, which helps distinguish acquired haemophilia from other bleeding disorders. When patient blood plasma is mixed with normal plasma in a mixing study, the aPTT remains prolonged rather than correcting, indicating the presence of an inhibitor rather than a simple factor deficiency.^[6][7]

The characteristic finding is that the prolongation of aPTT worsens after incubation compared to immediate mixing, which is typical behaviour of factor VIII autoantibodies. The final diagnosis is confirmed by demonstrating both reduced factor VIII levels and the presence of factor VIII neutralising activity through specialised testing.^[7]