Definition and epidemiology
Hemophilia is a group of inherited, X-linked recessive bleeding disorders caused by deficiency or dysfunction of a specific coagulation factor.
- Hemophilia A: deficiency of factor VIII; accounts for roughly 80-85% of cases
- Hemophilia B: deficiency of factor IX; accounts for roughly 15-20% of cases; also called Christmas disease
Both are inherited in an X-linked recessive pattern, so they almost always affect males. Female carriers are usually asymptomatic but can have mild bleeding tendencies, especially with extreme lyonization (skewed X-inactivation).
Hemophilia A occurs in approximately 1 in 5,000 male births; hemophilia B occurs in approximately 1 in 25,000-30,000 male births. About one-third of cases arise from de novo mutations with no family history. Historically called the "royal disease" due to its presence in European royal bloodlines descended from Queen Victoria.
- X-linked recessive: affects males; female carriers usually asymptomatic
- Hemophilia A (factor VIII) is more common than hemophilia B (factor IX), roughly 80-85% vs 15-20%
- Classic lab pattern: isolated prolonged aPTT, normal PT, normal platelet count, normal bleeding time
- Hemarthrosis (joint bleeding) is the hallmark clinical finding, not mucosal bleeding
- Mixing study corrects aPTT in factor deficiency but NOT in lupus anticoagulant
- Desmopressin works only in mild hemophilia A, never in hemophilia B
- Emicizumab mimics factor VIII and works even in patients with inhibitors
- Up to 25-30% of severe hemophilia A patients develop inhibitors against factor VIII
Etiology and risk factors
- Genetic mutation: mutations in the F8 gene (factor VIII, hemophilia A) or F9 gene (factor IX, hemophilia B), both located on the long arm of the X chromosome
- Inheritance pattern: X-linked recessive; affected fathers cannot transmit disease to sons (sons get Y chromosome) but all daughters become carriers
- Carrier mothers: have a 50% chance of transmitting the mutant allele to each son (who will be affected) and each daughter (who will be a carrier)
- De novo mutation: accounts for a significant minority of cases, particularly important when there is no family history
- Severity correlates with genotype: large deletions and inversions (e.g., intron 22 inversion in factor VIII gene) typically cause severe disease, while missense mutations often cause milder phenotypes
Risk factors are essentially genetic; there are no significant environmental or lifestyle risk factors for the inherited forms. A rare acquired form (acquired hemophilia A) results from autoantibodies against factor VIII and is associated with postpartum state, malignancy, autoimmune disease, and advanced age.
Pathophysiology
Factor VIII and factor IX are both essential components of the intrinsic coagulation pathway. Factor VIII acts as a cofactor for factor IXa, which activates factor X in the presence of calcium and phospholipid, propagating thrombin generation.
Deficiency of either factor impairs secondary hemostasis (the coagulation cascade) while primary hemostasis (platelet plug formation) remains intact. This explains the characteristic bleeding pattern:
- Deep bleeding: into joints (hemarthrosis), muscles, and soft tissues, rather than mucocutaneous bleeding
- Delayed bleeding: after trauma or surgery, bleeding may start hours later as the initial platelet plug forms normally but fails to be stabilized by fibrin
Disease severity is classified by residual factor activity:
| Severity | Factor activity | Clinical pattern |
|---|---|---|
| Severe | less than 1% | Spontaneous bleeding, recurrent hemarthrosis |
| Moderate | 1-5% | Bleeding after minor trauma |
| Mild | 5-40% | Bleeding only after surgery or major trauma |
Recurrent hemarthrosis leads to synovial hypertrophy, chronic inflammation, and progressive cartilage destruction, culminating in hemophilic arthropathy.
Clinical features
- Hemarthrosis: the hallmark finding; recurrent bleeding into large joints (knees, elbows, ankles) causing pain, swelling, and warmth; repeated episodes lead to a "target joint"
- Muscle hematomas: can cause compartment syndrome or nerve compression (e.g., iliopsoas hematoma causing femoral nerve palsy)
- Easy bruising and prolonged bleeding after minor cuts, dental procedures, or surgery
- Mucosal bleeding: epistaxis, gum bleeding (less prominent than in platelet disorders)
- Neonatal presentation: intracranial hemorrhage, prolonged bleeding after circumcision, or bleeding at the umbilical stump
- Severe disease: often presents in infancy or early childhood with spontaneous bleeding
- Mild disease: may not be diagnosed until significant hemostatic challenge (surgery, trauma) in adulthood
- Family history of bleeding in maternal male relatives is a useful clue but is absent in de novo cases
Diagnosis
Initial screening
- CBC: normal platelet count
- PT (prothrombin time): normal (extrinsic pathway unaffected)
- aPTT (activated partial thromboplastin time): prolonged (intrinsic pathway affected)
- Bleeding time: normal (primary hemostasis intact)
Confirmatory testing
- Mixing study: aPTT corrects when patient plasma is mixed 1:1 with normal plasma, confirming a factor deficiency rather than an inhibitor
- Specific factor assays: measure factor VIII and factor IX activity levels to confirm diagnosis, identify which factor is deficient, and establish severity
- Genetic testing: identifies the specific F8 or F9 mutation; useful for carrier detection and prenatal diagnosis
Additional considerations
- Von Willebrand factor level should be checked when factor VIII is low, since von Willebrand disease type 2N and acquired von Willebrand syndrome can mimic hemophilia A
- Inhibitor screening (Bethesda assay) is performed in patients who fail to respond to factor replacement or develop a new prolonged aPTT despite treatment, to detect alloantibody inhibitors against the infused factor
- Prenatal diagnosis via chorionic villus sampling or amniocentesis is available for known carriers
Differential diagnosis
- Von Willebrand disease: most common inherited bleeding disorder; affects both sexes; mucocutaneous bleeding pattern; low or dysfunctional von Willebrand factor with secondarily low factor VIII
- Factor XI deficiency: also causes isolated prolonged aPTT; more common in Ashkenazi Jewish population; generally milder bleeding
- Acquired hemophilia: autoantibody against factor VIII; occurs in older adults, postpartum women, or those with autoimmune disease/malignancy; no personal or family bleeding history
- Vitamin K deficiency / liver disease: prolongs both PT and aPTT, unlike isolated aPTT prolongation in hemophilia
- Lupus anticoagulant: prolongs aPTT but mixing study does NOT correct (distinguishes from factor deficiency) and is associated with thrombosis, not bleeding
- Platelet function disorders / thrombocytopenia: mucocutaneous bleeding pattern (petechiae, epistaxis) rather than deep tissue/joint bleeding; abnormal platelet count or function tests
Management
General principles
Management follows comprehensive hemophilia care center models endorsed by the World Federation of Hemophilia and major hematology societies, emphasizing prophylaxis over on-demand treatment where resources allow.
Factor replacement therapy
- Hemophilia A: recombinant or plasma-derived factor VIII concentrate
- Hemophilia B: recombinant or plasma-derived factor IX concentrate
- Prophylactic regimens: regular scheduled infusions to prevent spontaneous bleeding and joint damage; now standard of care for severe hemophilia in most guidelines
- On-demand treatment: factor given at the time of a bleeding episode; used for milder disease or where prophylaxis is not feasible
- Extended half-life factor products allow less frequent dosing
Non-factor and adjunctive therapies
- Desmopressin (DDAVP): stimulates release of endogenous factor VIII and von Willebrand factor; useful in mild hemophilia A only (not hemophilia B)
- Emicizumab: a bispecific antibody that mimics factor VIII function by bridging factor IXa and factor X; approved for prophylaxis in hemophilia A, including patients with inhibitors; administered subcutaneously
- Antifibrinolytics (tranexamic acid, aminocaproic acid): adjuncts for mucosal bleeding (dental procedures, epistaxis)
- Topical hemostatic agents for superficial bleeding
Management of inhibitors
- Patients who develop neutralizing alloantibodies against factor VIII or IX require bypassing agents such as recombinant activated factor VII or activated prothrombin complex concentrate during bleeds
- Immune tolerance induction (regular high-dose factor exposure) is used to eradicate inhibitors long-term
- Emicizumab provides effective prophylaxis in hemophilia A patients with inhibitors
Supportive measures
- Avoid intramuscular injections, NSAIDs, and antiplatelet agents
- Physical therapy to preserve joint function and prevent/manage hemophilic arthropathy
- Comprehensive care through specialized hemophilia treatment centers improves outcomes
- Gene therapy (adeno-associated virus vector delivering factor VIII or IX genes) has received regulatory approval in some countries and represents an emerging one-time treatment option, though guideline consensus on its routine use is still evolving
Complications and prognosis
- Hemophilic arthropathy: chronic joint damage from recurrent hemarthrosis; the leading cause of long-term disability
- Intracranial hemorrhage: a leading cause of hemophilia-related death, can occur spontaneously or after minor head trauma
- Inhibitor development: occurs in up to 25-30% of severe hemophilia A patients, complicating treatment and increasing morbidity
- Transfusion-related infections: historically HIV and hepatitis C from plasma-derived products in the pre-1990s era; now rare with recombinant products and improved screening
- Compartment syndrome and nerve palsy: from muscle hematomas
With modern prophylactic factor replacement, life expectancy approaches that of the general population and most patients lead active lives. Without treatment, severe hemophilia significantly shortens life expectancy and causes major disability from recurrent bleeding and joint destruction. Early initiation of prophylaxis in childhood is the strongest predictor of preserved long-term joint function.
"PaTT" the Pathway: aPTT tests the intrinsic Pathway (factors VIII, IX, XI, XII) — hemophilia A and B both prolong aPTT while PT stays normal.
Practice questions
1. A 3-year-old boy is brought to the emergency department after his parents noticed his right knee is swollen, warm, and painful following a minor fall. He has had two similar episodes in the past year. Laboratory studies show a normal platelet count, normal PT, and prolonged aPTT. Mixing study with normal plasma corrects the aPTT. Which of the following is the most likely diagnosis?
2. A 45-year-old woman who delivered a baby 3 months ago presents with extensive bruising and a large thigh hematoma with no prior personal or family history of bleeding. Laboratory studies show a prolonged aPTT that corrects on an immediate mixing study but becomes prolonged again (fails to correct) after incubation of the mixed plasma. Factor VIII activity is markedly reduced. Which of the following is the most likely underlying mechanism?
3. A 10-year-old boy with known severe hemophilia A is being started on prophylactic therapy. After several factor VIII infusions, his bleeding episodes continue despite seemingly adequate dosing, and his aPTT remains prolonged after infusion. Which of the following tests should be performed next to evaluate this finding?
Frequently asked questions
What causes hemophilia?
Hemophilia is caused by inherited mutations in the F8 gene (hemophilia A) or F9 gene (hemophilia B), both located on the X chromosome, leading to deficient clotting factor VIII or IX. It is inherited in an X-linked recessive pattern, so it almost always affects males, while female relatives can be carriers. About one-third of cases arise from a new mutation with no prior family history.
What are the first symptoms of hemophilia?
The first symptoms are often excessive bruising, prolonged bleeding after minor injuries or circumcision, and in severe cases, spontaneous bleeding into joints or muscles starting in infancy or early childhood. Joint bleeding (hemarthrosis) causing pain and swelling in a knee, elbow, or ankle is a classic early presentation once a child starts crawling or walking. Milder forms may not become apparent until surgery or significant trauma occurs later in life.
How is hemophilia diagnosed?
Hemophilia is diagnosed through blood tests showing a prolonged aPTT with a normal PT and normal platelet count, followed by specific factor VIII and factor IX assays to confirm which factor is deficient and determine severity. A mixing study helps confirm a true factor deficiency. Genetic testing can identify the specific mutation, which is useful for family counseling and prenatal diagnosis.
Is hemophilia curable?
Hemophilia is not curable with standard treatment, but it is highly manageable with regular factor replacement therapy or newer agents like emicizumab, allowing a near-normal lifespan and lifestyle. Gene therapy, which delivers a working copy of the factor gene, has been approved in some countries and may offer long-term or potentially one-time correction, but it is not yet considered a universal cure and long-term outcome data are still accumulating.
Hemophilia vs von Willebrand disease — what is the difference?
Hemophilia is an X-linked disorder affecting mainly males with deep tissue and joint bleeding, caused by deficiency of factor VIII or IX, while von Willebrand disease affects both sexes and causes primarily mucocutaneous bleeding (nosebleeds, gum bleeding, heavy menstrual bleeding) due to deficient or dysfunctional von Willebrand factor. Von Willebrand disease is also more common overall and often milder. Lab testing and family bleeding patterns help distinguish the two.
Key drugs
Related conditions and differentials
Sources and further reading
StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: D68
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.