Hemophilia C is a bleeding disorder caused by a shortage of factor XI, a protein your body needs to form blood clots. Unlike the more well-known hemophilia A and B, hemophilia C is generally milder, rarely causes spontaneous bleeding, and follows a different inheritance pattern. It’s also called factor XI deficiency.
How It Differs From Hemophilia A and B
Hemophilia A results from a deficiency of clotting factor VIII, and hemophilia B from factor IX. Both are inherited through the X chromosome, which is why they overwhelmingly affect males. Hemophilia C works differently. It’s caused by mutations in the F11 gene, which carries instructions for making the factor XI protein. This gene sits on chromosome 4, not a sex chromosome, so hemophilia C affects men and women equally.
The practical difference is significant. People with hemophilia A or B often deal with spontaneous bleeding into joints and muscles, sometimes requiring regular preventive treatment. People with hemophilia C don’t experience joint or muscle bleeds. Their bleeding problems tend to surface only during surgery, dental procedures, serious injuries, or childbirth. Someone can live with hemophilia C for years without knowing they have it.
Who Gets It
Hemophilia C is the most common of the rare inherited clotting factor deficiencies. It occurs in all ethnic groups but is dramatically more prevalent among Ashkenazi Jewish populations. Research on this community found that roughly 5.5% to 11% of Ashkenazi Jews carry one copy of the mutant gene (heterozygotes), while about 1 in 450 have two copies and develop severe deficiency. This makes factor XI deficiency one of the most common genetic disorders in this population, alongside conditions like Tay-Sachs and Gaucher disease.
Outside Ashkenazi populations, hemophilia C is considerably rarer, though exact global numbers are harder to pin down because mild cases often go undiagnosed.
Severity Levels
How much factor XI your body produces determines the classification of your deficiency, though the relationship between factor levels and actual bleeding risk is surprisingly unpredictable.
- Severe deficiency: Factor XI activity below 15% to 20% of normal. This occurs in people who inherited a defective gene from both parents (homozygotes or compound heterozygotes).
- Partial deficiency: Factor XI activity between 20% and 70% of normal. This is typical of heterozygotes, people who carry one normal copy and one mutant copy of the gene.
Here’s what makes hemophilia C unusual: someone with very low factor levels may bleed very little, while someone with only moderately reduced levels can sometimes bleed more than expected. The severity of bleeding doesn’t track neatly with the measured factor level the way it does in hemophilia A or B. This unpredictability makes management decisions trickier for both patients and their medical teams.
Symptoms and Bleeding Patterns
Most people with hemophilia C notice bleeding problems only in specific situations. The most common trigger is dental surgery or tooth extraction, where the tissues of the mouth are rich in enzymes that break down clots. Tonsil removal is another classic setting for unexpected bleeding.
Day-to-day symptoms, when they occur, tend to be mild: nosebleeds, easy bruising, blood in urine, or unusually heavy and prolonged menstrual periods. Some male infants have excessive bleeding after circumcision, which can be the first clue to the diagnosis. After major surgery, a serious injury, or childbirth, bleeding can become prolonged and harder to control, which is the primary medical concern with this condition.
Pregnancy and Childbirth Risks
Hemophilia C poses real but manageable risks during pregnancy and delivery. The rate of postpartum hemorrhage (heavy bleeding after birth) is notably elevated. One study tracking over 200 deliveries found a postpartum hemorrhage rate of 11%, and a broader review of nearly 500 deliveries put the rate at 18%. For comparison, the general population rate is roughly 3% to 5%.
Women with moderate or severe factor XI deficiency typically have their clotting factor levels checked early in pregnancy and again around 36 weeks. Delivery is ideally planned at a facility with specialists in blood disorders, maternal-fetal medicine, and access to blood products. Certain procedures that increase bleeding risk for the baby, like fetal scalp electrodes, are generally avoided. Male infants born to parents who carry the gene should not be circumcised until testing can determine whether the baby is affected.
How It’s Diagnosed
Hemophilia C is often discovered by accident, either during routine pre-surgical blood work or after an unexpectedly heavy bleed during a procedure. Standard clotting tests may show a prolonged activated partial thromboplastin time (a test measuring how long blood takes to clot through one particular pathway), which prompts a specific factor XI activity level test. That measurement confirms the diagnosis and determines severity.
If you have a family history of hemophilia C, particularly if you’re of Ashkenazi Jewish descent, testing before any planned surgery is worthwhile. Knowing your factor XI level in advance allows your surgical team to prepare appropriately rather than reacting to unexpected bleeding.
Treatment and Management
Because hemophilia C rarely causes spontaneous bleeding, most people don’t need ongoing treatment. Management centers on preventing and controlling bleeding during high-risk events like surgery, dental work, or delivery.
When treatment is needed, options include fresh frozen plasma (which contains factor XI along with other clotting proteins) or, where available, a concentrated factor XI product. Antifibrinolytic medications, which help stabilize clots once they form, are commonly used after delivery or dental procedures. These can be given intravenously during an acute bleed or taken orally to prevent delayed bleeding in the days that follow.
One important complication to be aware of: some people with severe factor XI deficiency (particularly those with levels below 1%) can develop inhibitors, antibodies that neutralize factor XI when it’s given as a treatment. This makes replacement therapy ineffective and requires alternative strategies to manage bleeding. It’s uncommon, but it’s one reason that treatment decisions for hemophilia C are made on a case-by-case basis rather than following a simple formula.
People with hemophilia C are generally advised to avoid aspirin and nonsteroidal anti-inflammatory drugs like ibuprofen, which impair platelet function and can worsen bleeding. Acetaminophen is the safer choice for pain relief. Before any surgical or dental procedure, letting your care team know about your diagnosis allows them to plan ahead with appropriate preventive measures.