Hemophilia is an inherited bleeding disorder in which the blood does not clot normally. Hemophilia A, also known as classical hemophilia, is caused by having low levels of a protein called clotting factor VIII.  Hemophilia B, also known as Christmas disease, is caused by having low levels of clotting factor IX.

People with hemophilia bleed more than normal after an injury, surgery, or dental procedure. The disorder can be mild, moderate, or severe. In mild forms, the disorder may be diagnosed only after a surgery or serious injury. In severe cases, heavy bleeding occurs after minor injury or can even happen spontaneously without any injury. Hemophilia can be diagnosed by a blood test, which may be done if other family members have the condition. 

Hemophilia mainly affects males. 


Diagnosis is determined by screening blood tests and specific clotting factor assay tests. Screening blood tests show if the blood is clotting properly and specific clotting factor tests indicate the type of hemophilia (A or B) and the severity.

Screening blood tests typically include the Activated Partial Thromboplastin Time (APTT) Test, which measures:

  • How long it takes for blood to clot
  • Clotting ability of factors VIII, IX, XI, and XII—blood clots more slowly if any of these clotting factors are too low

If the APTT is longer than normal, a test called an APTT Mixing Study is done. If the results of the APTT Mixing Study indicate that the level of one of the clotting factors may be low, specific testing for each clotting factor can be performed to determine the activity level. If the Factor VIII level is low, the individual may have Hemophilia A and if the Factor IX level is low, the individual may have Hemophilia B. These clotting factor tests also indicate the severity of the deficiency.


Hemophilia is most often treated by replacing the missing blood clotting factor so that the blood can clot properly. The treatment products, known as clotting factor concentrates, are typically injected directly into the veins. This therapy can be used to both prevent and treat episodes of bleeding.

The two main types of clotting factor concentrates available are human plasma-derived factor concentrates made from donated blood and recombinant factor VIII concentrate, which is genetically engineered using DNA technology. 

A medication called Hemlibra (emicizumab) can also be used in Hemophilia A patients to prevent bleeding episodes.  Another treatment which may be used is control bleeding in patients with Hemophilia A is desmopressin (DDAVP). This medication is similar to a naturally-occurring hormone. It works by increasing an individual’s own factor VIII level temporarily so that clotting factors are not needed. It may be effective for mild cases of hemophilia in select indications.   

Additional medications useful in patients with Hemophilia A or B include epsilon-aminocaproic acid and tranexamic acid—antifibrinolytic agents that help stabilize clots once they are formed.

Patients with hemophilia are treated at the Mount Sinai Hemophilia Treatment Center.