Diagnosis of Hemophilia

Hemophilia is a bleeding disorder that stems from having little to no blood clotting factors, which are specific proteins needed for blood to clot. The disorder usually is inherited, although it also can be acquired.

Hemophilia diagnosis typically begins by examining a person’s family history and the results of several blood tests.

Family history

A family history of hemophilia is present in about 70% of cases, making it a key factor to consider when diagnosing the disorder. Severe hemophilia often is diagnosed within the first year of life, while milder forms of the disease may go unnoticed until adulthood.

Expectant parents with a family history of the disorder may request their unborn child to be tested. Amniocentesis and chorionic villus sampling are two prenatal screening tests that can be used to identify genetic mutations associated with hemophilia in the unborn fetus.

Amniocentesis consists of using a needle to remove a small amount of amniotic fluid from the womb. The fluid is examined in the lab for the presence of hemophilia-causing genetic mutations. It typically is performed during the second trimester of pregnancy.

Chorionic villus sampling involves threading a thin tube through the vagina and cervix to remove a small tissue sample from the placenta, which is the temporary organ that provides oxygen and nutrients to the developing fetus. The collected sample is examined in a specialized lab to assess the presence of mutations in clotting factor genes. This procedure can be performed after the 11th week of pregnancy.

Blood tests

Blood tests used to diagnose hemophilia can be classified as either screening tests, which are used to determine whether blood clots properly, or clotting factor tests, which are used to identify the specific type and severity of hemophilia.

Screening tests

Complete blood count (CBC)

A CBC is a standard way to measure the size and number of red blood cells, as well as the number of various types of white blood cells, platelets, and hemoglobin, which is the oxygen-carrying protein found inside red blood cells. Although a CBC often is normal for people with hemophilia, hemoglobin levels and red blood cell counts may be low if a person experiences unusually heavy or prolonged bleeds.

Activated partial thromboplastin time (APTT) test

This test measures the clotting abilities of factors VIII, IX, XI, and XII in terms of the number of seconds it takes for a clot to form in a sample of blood. In patients with hemophilia, this process may take longer than normal due to the lack of some of these clotting factors.

Prothrombin time test (PTT)

This test complements the APTT by measuring how long it takes for blood to clot through the actions of factors I, II, V, VII, and X. In most patients with hemophilia A and B results from this test will be normal, as these patients typically lack factor VIII and IX, respectively.

Fibrinogen test

Fibrinogen is another name for clotting factor I. A fibrinogen activity test measures how well fibrinogen is helping a blood clot to form, while a fibrinogen antigen test measures the amount of fibrinogen in the blood.

Clotting factor tests

Also known as factor assays, these tests are used to identify the specific type of hemophilia a patient has, as well as to assess its severity. These points are critical to being able to provide effective and appropriate treatment, making this test necessary to establish a diagnosis.

Hemophilia severity generally is classified as either: mild, when a patient has 5–40% of normal clotting factor activity levels; moderate, when clotting factor activity levels are 1–5% of what would be expected; or severe, when clotting factor activity levels are less than 1% of normal.


Last updated: July 15, 2021


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