Severe vs. mild hemophilia A
Reviewed by If you have hemophilia A, you may wonder what it means if your condition is classified as mild, moderate, or severe. While all forms of hemophilia A affect blood clotting, the severity of the condition influences the frequency of bleeding episodes, what may trigger them, the treatments your healthcare team recommends, and your risk of long-term complications.
Understanding the severity of hemophilia A can help you make more sense of your symptoms, better understand your treatment plan, and know what to expect over time.
Hemophilia A severity depends on factor VIII levels
Hemophilia A is a bleeding disorder caused by low levels or reduced activity of factor VIII (FVIII), a protein that helps your blood clot after an injury. The amount of working FVIII in your blood determines how severe your hemophilia A is.
Approximately 60% of people with hemophilia A have the severe form, which is usually diagnosed during infancy or early childhood. Mild hemophilia A, however, may go undiagnosed for years because symptoms are often mild and may not appear until after surgery, dental work, or a significant injury.
Your healthcare provider measures your factor VIII activity to determine your factor VIII deficiency range and classify the severity of your hemophilia A.
Based on the results, hemophilia A is classified into one of three severity levels:
- Severe: Less than 1% of normal FVIII activity
- Moderate: 1%-5% of normal FVIII activity
- Mild: 6%-49% of normal FVIII activity
Your test results may also be reported in international units per milliliter (IU/mL). This measurement reflects how well your FVIII works rather than how much of the protein is present in your blood.
Normal FVIII activity ranges from 0.5-1.5 IU/mL, which is equivalent to 50%-150% of normal clotting activity. Hemophilia A severity generally corresponds to the following FVIII activity levels:
- Mild hemophilia A: 0.06-0.49 IU/mL (6%-49% FVIII activity)
- Moderate hemophilia A: 0.01-0.05 IU/mL (1%-5% FVIII activity)
- Severe hemophilia A: Less than 0.01 IU/mL (less than 1% FVIII activity)
Knowing your FVIII activity level can help you better understand your diagnosis and why your healthcare provider recommends a particular treatment plan. If you have questions about your results, ask your provider what they mean for your bleeding risk and overall care.
Bleeding triggers and frequency across clinical levels
One of the biggest differences between mild, moderate, and severe hemophilia A is how often bleeding episodes occur and what causes them. In general, the lower your factor VIII activity level, the greater your risk of bleeding. However, your symptoms don’t always correlate with your severity classification, so it’s important to discuss any concerns with your healthcare provider.
If you have severe hemophilia A, you may experience:
- spontaneous bleeding without an obvious injury or with a minimal injury
- bleeding into the joints, called hemarthrosis, which most often affects the knees, ankles, or elbows
Repeated joint bleeds in people with severe hemophilia A also can lead to chronic joint damage, known as hemophilic arthropathy, which may cause pain, stiffness, and reduced mobility.
If you have mild hemophilia symptoms, you are less likely to experience frequent bleeding. Instead, you may have:
- bleeding after surgery, dental procedures, or a significant injury
- few or no spontaneous bleeding episodes
- a lower risk of long-term joint damage because repeated joint bleeding is uncommon
If you have moderate hemophilia A, your symptoms can vary widely. Some people have bleeding patterns similar to those with mild hemophilia A, while others experience more frequent bleeding that resembles severe disease.
It’s also important to remember that your symptoms may not always match your diagnosis. A recent study estimated that about 20% of people with mild or moderate hemophilia A experience bleeding severe enough to increase their risk of joint damage if it isn’t treated appropriately.
If your bleeding episodes seem more frequent or severe than expected, talk with your healthcare provider. Your doctor can reassess your treatment plan and determine whether changes are needed.
Prophylactic vs. situational treatment
Your hemophilia A treatment plan depends on several factors, but primarily your factor VIII activity level, bleeding history, lifestyle, and overall health. While disease severity plays an important role, treatment is individualized based on your needs.
If you have severe hemophilia A, your healthcare provider will likely recommend prophylactic treatment, or regular therapy designed to help prevent bleeding episodes before they occur. The goal is to maintain enough factor VIII activity to reduce spontaneous bleeding and protect your joints from long-term damage.
Prophylactic treatment may include:
- regular infusions of factor VIII replacement therapy
- use of emicizumab, an antibody-based therapy, to mimic the function of factor VIII and help prevent bleeding episodes
If you have mild hemophilia A, you may not need ongoing prophylactic treatment. Instead, your healthcare provider may recommend on-demand treatment, which is given to stop or control bleeding after it starts or before situations that increase your risk of bleeding, such as surgery or dental procedures. Depending on your individual needs, treatment may involve factor VIII replacement therapy, emicizumab, or other medications.
Keep in mind that treatment recommendations aren’t based on severity alone. Some people with mild and moderate hemophilia A or frequent bleeding episodes may also benefit from prophylactic treatment. Your healthcare provider will recommend the approach that’s best for you based on your bleeding pattern and individual risk factors.
Advances in treatment have made it possible for many people with hemophilia A to prevent bleeding episodes more effectively and stay active. If you’re experiencing frequent bleeds, joint pain, or changes in your symptoms, talk with your healthcare team. Your doctors can help determine whether your current treatment plan is still meeting your needs.
Hemophilia News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
