Hemophilia C is a rare inherited bleeding disorder caused by a shortage of factor XI, one of the 13 proteins your blood needs to form clots. It affects roughly 1 in 1 million people worldwide and is considerably milder than the better-known hemophilia A and B. Unlike those types, hemophilia C rarely causes spontaneous bleeding and never targets the joints or muscles. Most people discover they have it only after unusual bleeding during surgery, dental work, or childbirth.
How Factor XI Fits Into Clotting
When you’re injured, your body kicks off a chain reaction called the coagulation cascade, where clotting proteins activate one another in sequence until a stable clot seals the wound. Factor XI sits in the middle of that chain. Without enough of it, the cascade slows down and clots form too slowly or too weakly to stop bleeding efficiently.
The gene responsible for making factor XI is called F11. Mutations in this gene either reduce the amount of factor XI your body produces or prevent it from being made at all. The result is the same: your blood takes longer to clot than it should, particularly at sites rich in blood vessels like the gums, nasal passages, and urinary tract.
How It Differs From Hemophilia A and B
All three types of hemophilia involve a missing or defective clotting protein, but the similarities largely end there. Hemophilia A (factor VIII deficiency) and hemophilia B (factor IX deficiency) are X-linked conditions, meaning a child can inherit them from a single parent carrying the affected gene. They often cause painful, recurrent bleeding into joints and muscles, and the severity of symptoms closely tracks the level of the missing clotting factor in the blood.
Hemophilia C breaks those patterns in several ways. It follows an autosomal recessive inheritance pattern, so a child typically needs to receive the abnormal F11 gene from both parents to develop the full condition. And the relationship between factor levels and symptoms is unpredictable. Someone with very low factor XI levels may bleed only mildly, while another person with the same lab results might bleed more. This makes hemophilia C harder to classify neatly into “mild” and “severe” categories the way clinicians do with hemophilia A and B.
Who Gets It
Hemophilia C can affect anyone regardless of sex, which is another departure from hemophilia A and B (both far more common in males). It appears across all ethnic groups, but it is strikingly concentrated among Ashkenazi Jewish populations, where the carrier rate reaches 8 to 9 percent. This high frequency is linked to the historical prevalence of marriage within the community, which increased the odds of both parents carrying the same F11 mutation.
If both parents carry one copy of the abnormal gene, each pregnancy carries a 25% chance the child will have hemophilia C, a 50% chance the child will be a carrier without symptoms, and a 25% chance the child will inherit two normal copies of the gene.
Symptoms and Bleeding Patterns
Many people with hemophilia C go years without a noticeable bleeding problem. The condition tends to reveal itself in situations that challenge the clotting system: a tooth extraction, a tonsillectomy, a heavy menstrual period, or a significant injury. Bleeding after surgery is the most common red flag.
Typical bleeding sites include the mouth and gums, the nose, and the urinary tract. Heavy or prolonged menstrual bleeding is common in women with the condition. What you won’t see in hemophilia C is the spontaneous joint bleeding (hemarthrosis) that defines severe hemophilia A and B. That distinction matters because it means most people with hemophilia C don’t face the chronic joint damage that can be disabling in other forms of hemophilia.
The unpredictable relationship between factor levels and actual bleeding risk is one of the trickiest parts of managing the condition. A person classified as having “major” deficiency (factor XI activity below 15% of normal) doesn’t necessarily bleed more than someone with a moderate deficiency. Doctors often rely more on a patient’s personal and family bleeding history than on lab values alone when estimating risk.
How It’s Diagnosed
Hemophilia C is usually suspected when routine pre-surgical blood work shows a prolonged clotting time, specifically on a test called the activated partial thromboplastin time (aPTT). A normal aPTT effectively rules the condition out, while a prolonged one prompts further testing to measure factor XI activity directly. Major deficiency is defined as factor XI activity below 15 IU/dL, though again, that number alone doesn’t predict how much someone will bleed.
Because many people with hemophilia C have no symptoms in daily life, the diagnosis is frequently made in adulthood, often right before or after a surgical procedure. Genetic testing can confirm the specific F11 mutation and is useful for family screening.
Treatment Before Surgery and Procedures
Day-to-day treatment is rarely needed. The condition demands attention mainly around surgery, dental extractions, and other procedures that carry bleeding risk. The standard approach is to give fresh frozen plasma (FFP) before and during the operation, which temporarily supplies the missing factor XI and brings clotting closer to normal.
For less invasive procedures, or as an add-on to plasma, doctors sometimes use antifibrinolytic medications. These drugs work by preventing clots from breaking down too quickly once they’ve formed, which is especially helpful for bleeding in the mouth after dental work. They can be taken as a pill or used as a mouthwash.
One complication worth knowing about: up to 33% of people with severe factor XI deficiency (activity below 1%) can develop inhibitors, antibodies that attack the replacement factor XI received through plasma products. When that happens, alternative strategies are needed, which is part of why treatment plans should be individualized.
Pregnancy and Childbirth
Hemophilia C poses specific risks during and after delivery. Roughly 20% of pregnant women with severe factor XI deficiency experience excessive bleeding at delivery if no preventive treatment is given. Postpartum hemorrhage, both in the first 24 hours and in the weeks that follow, is significantly more common in women with partial or severe deficiency, occurring in 13 to 31% of affected women in published studies.
Managing pregnancy with hemophilia C calls for coordination among obstetricians, hematologists, and anesthesiologists. One key question is whether epidural or spinal anesthesia is safe, since these procedures carry a small risk of bleeding around the spinal cord. The decision is made case by case, weighing each woman’s factor levels, bleeding history, and personal preferences. In some cases, low doses of a clotting factor concentrate are given before delivery or before regional anesthesia to reduce risk.
Living With Hemophilia C
For most people, hemophilia C has a minimal impact on daily life. You won’t need regular infusions or factor replacement the way someone with severe hemophilia A might. The main practical steps are making sure every healthcare provider you see knows about your diagnosis, planning ahead for surgeries or dental procedures, and being aware of bleeding symptoms after any significant trauma. Women should discuss their diagnosis with their OB-GYN, particularly if they experience heavy periods or are planning a pregnancy.
Carrying a medical alert card or wearing a medical ID bracelet is a simple precaution that ensures emergency responders know about your condition if you’re unable to communicate. Because the disorder is rare and unfamiliar even to some clinicians, having that information immediately available can prevent delays in appropriate care.