Acquired haemophilia – Diagnostics – Overview of Information and Clinical Research

Diagnosing acquired haemophilia can be challenging because this rare bleeding disorder often appears suddenly in people who have never experienced bleeding problems before. Understanding when to seek testing and what diagnostic methods doctors use is crucial for timely identification and treatment of this potentially life-threatening condition.

Introduction: Who Should Undergo Diagnostics

Any person who suddenly develops unexplained bleeding symptoms without a previous history of bleeding problems should seek medical evaluation immediately. This is especially important for older adults and women in late pregnancy or who have recently given birth, as these groups are most commonly affected by acquired haemophilia.^[1]

Acquired haemophilia differs dramatically from the hereditary form of the disease. People with this condition would have been completely well before, with normal blood clotting throughout their lives. The sudden appearance of bleeding symptoms in someone without any personal or family history of bleeding disorders is a significant warning sign that requires prompt medical attention.^[3]

The condition presents in various ways. Some people experience severe, life-threatening bleeding, while others may have only mild bleeding or even no bleeding at all. Because of this variability, doctors must remain vigilant when they discover certain laboratory abnormalities during routine testing, even in patients who are not actively bleeding. Approximately 10% of patients with acquired haemophilia do not present with any bleeding symptoms at all, making laboratory findings the only indication of the disease.^[6]

Diagnostic testing becomes especially important before any surgical procedure or invasive medical intervention. A prolonged activated partial thromboplastin time (a laboratory measurement that checks how long it takes blood to clot) should never be ignored before these procedures, even if the patient appears healthy and has no bleeding symptoms. Identifying acquired haemophilia before surgery can prevent potentially catastrophic bleeding complications.^[6]

⚠️ Important

If you experience sudden, unexplained bleeding—such as large bruises appearing without injury, bleeding from your gums that won’t stop, blood in your urine or stool, or severe muscle bleeding—seek medical attention immediately. This is especially critical if you are over 60 years old or are pregnant or recently gave birth, as these are the peak times when acquired haemophilia typically appears.

Classic Diagnostic Methods

The diagnostic process for acquired haemophilia begins with recognizing the clinical picture and proceeds through a series of increasingly specific laboratory tests. The first clue typically comes from routine blood work that reveals an unexpected abnormality.^[4]

Initial Laboratory Screening

The most important initial finding is a prolonged activated partial thromboplastin time, commonly abbreviated as aPTT. This test measures how long it takes for blood to clot through a specific pathway in the body’s clotting system. In acquired haemophilia, this time is extended beyond normal limits. Importantly, other basic clotting tests remain normal—the prothrombin time (PT), bleeding time, and platelet count all show normal results. This pattern of one abnormal test with others remaining normal helps doctors narrow down the possibilities.^[4]

The bleeding time test specifically measures how long it takes for a small cut on the skin to stop bleeding, while platelet count tells doctors how many of these tiny clotting cells are circulating in the blood. When these tests are normal but the aPTT is prolonged, it suggests a problem with specific clotting factors rather than with platelets or the blood vessels themselves.^[1]

The Mixing Study

Once a prolonged aPTT is discovered, doctors perform what is called a mixing study. This crucial test helps distinguish between two different causes of prolonged clotting time: a deficiency of clotting factors versus the presence of an inhibitor (an antibody that blocks clotting factors).^[7]

In a mixing study, the patient’s blood plasma is mixed with normal plasma from a healthy person. If the prolonged aPTT corrects to normal after mixing, this suggests the patient simply lacks sufficient clotting factors, which are replaced by the normal plasma. However, if the aPTT remains prolonged even after mixing, this indicates the presence of an inhibitor—an antibody that is actively blocking the clotting factors, preventing them from working properly.^[7]

The mixing study in acquired haemophilia has a characteristic pattern. The test is performed both immediately after mixing the blood samples and again after incubating the mixture at body temperature for one to two hours. In acquired haemophilia, the aPTT may be only slightly prolonged immediately after mixing, but becomes significantly more prolonged after incubation. This time-dependent pattern occurs because the autoantibodies against factor VIII work slowly, requiring time and warmth to neutralize the clotting factor.^[7]

Factor VIII Level and Inhibitor Detection

After the mixing study suggests the presence of an inhibitor, doctors measure the level of factor VIII in the blood. In acquired haemophilia, this level is reduced, confirming that factor VIII specifically is affected. However, measuring the level alone is not sufficient—doctors must also confirm that neutralizing antibodies against factor VIII are present.^[4]

The presence and strength of these antibodies are measured using specialized tests called the Bethesda assay or its modification, the Nijmegen-modified Bethesda assay. These tests quantify how much inhibitory activity is present in the blood, with results expressed in Bethesda units (BU). This measurement is important not only for confirming the diagnosis but also for guiding treatment decisions later.^[6]

The Nijmegen modification is particularly useful because it is more sensitive and can detect lower levels of inhibitors than the original Bethesda assay. This increased sensitivity helps ensure that no cases are missed, even when inhibitor levels are relatively low.^[6]

Testing Other Clotting Factors

Even after identifying low factor VIII levels and detecting factor VIII inhibitors, doctors typically test other clotting factors as well. This step ensures that factor VIII is the only clotting factor affected and helps establish what doctors call “inhibitor specificity.” In acquired haemophilia, only factor VIII should be affected, while other clotting factors remain at normal levels.^[4]

Excluding Other Conditions

Several other conditions can cause a prolonged aPTT and must be ruled out before confirming a diagnosis of acquired haemophilia. One important condition to exclude is lupus anticoagulant, an antibody that prolongs clotting tests but does not actually cause bleeding—in fact, it increases the risk of blood clots rather than bleeding.^[7]

To distinguish lupus anticoagulant from factor VIII inhibitors, doctors perform additional specialized tests such as the dilute Russell viper venom time and the kaolin clotting time. The pattern of results on the mixing study also helps make this distinction. With lupus anticoagulant, the aPTT values in the mixing study are similarly prolonged both immediately and after incubation, whereas with factor VIII inhibitors, the prolongation worsens with incubation.^[4]

If a patient is already taking the blood-thinning medication heparin, special testing must be done to exclude its effect on clotting test results. Heparin can prolong the aPTT for different reasons, and doctors need to account for this when interpreting the results.^[4]

Investigating Underlying Causes

Once acquired haemophilia is diagnosed, doctors typically search for any underlying conditions that might have triggered the development of autoantibodies. Approximately half of all cases are associated with other medical conditions, while the other half are considered idiopathic, meaning no underlying cause can be identified.^[1]

Common associated conditions include autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and other connective tissue disorders. Various types of cancer, both solid tumors and blood cancers, can also be associated with acquired haemophilia. This diagnostic investigation may include blood tests for autoimmune markers, imaging studies to look for cancers, and other evaluations based on the patient’s symptoms and medical history.^[1]

Diagnostics for Clinical Trial Qualification

When patients with acquired haemophilia are being considered for enrollment in clinical trials, additional standardized diagnostic criteria and monitoring procedures are typically required. These ensure that all participants in the study have properly confirmed diagnoses and that their progress can be accurately tracked and compared.^[6]

Baseline Assessment Requirements

Clinical trials for acquired haemophilia typically require comprehensive baseline testing before a patient can be enrolled. This includes confirmation of the diagnosis through all the standard laboratory tests described above, with specific minimum or maximum thresholds for factor VIII levels and inhibitor titers. For example, some trials may only include patients with factor VIII levels below a certain percentage of normal or with inhibitor titers within a specific range.^[4]

The baseline assessment also documents the severity and location of any bleeding symptoms, as this information is crucial for measuring whether treatments being studied in the trial are effective. Doctors carefully record details about bruising, muscle bleeds, bleeding into soft tissues, and any other bleeding manifestations.^[1]

Repeated Monitoring Tests

Throughout a clinical trial, participants undergo regular repeat testing to monitor their response to the treatment being studied. This typically includes frequent measurements of factor VIII levels and inhibitor titers, often performed weekly or at other regular intervals. These serial measurements help researchers understand how quickly the treatment works and how long its effects last.^[6]

The Bethesda assay or Nijmegen-modified Bethesda assay is repeated regularly to track changes in inhibitor levels. A declining inhibitor titer suggests that the treatment is working to eliminate the autoantibodies, while stable or rising levels may indicate that the treatment needs to be adjusted or changed.^[6]

Specialized Prognostic Testing

Some clinical trials may include more specialized testing beyond the standard diagnostic procedures. Research has identified certain laboratory markers that may help predict which patients will respond well to treatment and which may need more aggressive therapy. These prognostic markers include the factor VIII activity level at presentation, the inhibitor titer, and the specific type of antibody involved (the autoantibody isotype).^[6]

These markers help researchers stratify patients into different risk groups, which can be important for designing treatment strategies and understanding trial results. Higher inhibitor titers and lower factor VIII levels at diagnosis are generally associated with more challenging cases that may take longer to achieve remission.^[6]

Safety Monitoring

Clinical trials also require extensive safety monitoring through regular blood tests and physical examinations. Since treatments for acquired haemophilia often involve medications that suppress the immune system, trials include monitoring for infections and other complications. Complete blood counts, kidney function tests, liver function tests, and other assessments may be performed regularly to ensure patient safety throughout the trial.^[10]

Any bleeding episodes that occur during the trial are carefully documented and assessed. Doctors record the location, severity, and duration of bleeding, as well as what treatments were needed to control it. This information helps researchers understand the effectiveness and safety of the treatments being studied.^[10]

Prognosis and Survival Rate

Prognosis

The outlook for people with acquired haemophilia depends on several factors, including how quickly the condition is diagnosed and treated, the severity of bleeding symptoms, the patient’s age, and the presence of other medical conditions. The bleeding pattern of acquired haemophilia is variable, ranging from life-threatening hemorrhages to mild bleeding or even no bleeding at all in some cases. Most patients who present with severe bleeding typically experience these dangerous episodes during the initial several weeks after diagnosis, though life-threatening bleeding can occur at any point if appropriate treatment is not initiated.^[1]

Treatment has two major goals that influence prognosis: controlling acute bleeding episodes and eliminating the antibodies causing the disease. The median time to achieve remission—meaning the autoantibodies are eliminated and factor VIII levels return to normal—is approximately 5 weeks, though this varies considerably between individuals. About 60% to 80% of patients achieve remission with immunosuppressive therapy, which involves medications that calm the overactive immune system.^[11]

Several laboratory findings at the time of diagnosis can help predict outcomes. Patients with lower factor VIII activity levels at presentation, higher inhibitor titers, and certain types of autoantibodies may have more difficulty achieving remission and face higher risks of complications. These prognostic markers help doctors determine which patients may need more intensive treatment approaches.^[6]

Patients with underlying conditions such as autoimmune diseases or cancer may have different outcomes depending on whether the associated condition can be successfully treated or controlled. In cases where acquired haemophilia develops after childbirth, the prognosis is generally favorable, with many women experiencing spontaneous resolution of the condition within months.^[1]

Survival Rate

Acquired haemophilia carries significant mortality risk, with overall death rates reported in various studies ranging from 20% to 70%, depending on the patient population studied. The wide variation in these figures reflects differences in study populations, time periods, and treatment approaches. More recent registry data suggests mortality rates are typically in the lower part of this range with modern treatment approaches.^[7]

The causes of death in patients with acquired haemophilia are varied. Approximately 50% of deaths are attributed to the underlying medical conditions associated with the disease, such as cancer or severe autoimmune disorders, rather than to bleeding complications directly. Infections account for approximately 5% to 15% of deaths, which is particularly concerning given that many treatments for acquired haemophilia suppress the immune system. Major bleeding episodes themselves account for about 4% of deaths, though this risk is highest early in the disease course before diagnosis and treatment are established.^[7]

Advanced age is an important risk factor for poorer outcomes. Since acquired haemophilia most commonly affects elderly individuals, many patients have multiple other health conditions that complicate treatment and recovery. The presence of medications such as antiplatelet agents (drugs that prevent blood clots) may worsen bleeding complications and influence overall survival.^[6]

Mortality rates are particularly concerning when the condition is not promptly diagnosed and treated. Early recognition of acquired haemophilia and immediate initiation of appropriate therapy—both to control bleeding and to eliminate the autoantibodies—can significantly improve survival outcomes. Access to specialized care at comprehensive haemophilia treatment centers has been associated with better outcomes, as these centers have experience managing this rare and complex condition.^[4]

One encouraging finding is that patients who achieve complete remission—meaning their autoantibodies disappear and factor VIII levels return to normal—generally have good long-term outcomes. However, a small percentage of patients do not respond to initial treatment or experience relapse of their condition after apparent remission, and these individuals face ongoing risks.^[3]

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