Bleeding Disorders Glossary

These terms are commonly used throughout the hemophilia and Community Counts sites.


A starting point used for comparisons. For example, the baseline factor level is the level of clotting factor VIII (factor eight) or factor IX (factor nine) occurring naturally in the blood that can help to stop bleeding. The baseline factor level and other laboratory values may help healthcare providers determine the severity of a patient’s bleeding disorder.

Blood product

A substance taken from donated blood that may be used in the treatment of hemophilia and other blood problems. Whole blood, packed red blood cells, fresh-frozen plasma, platelets, and cryoprecipitate are all types of blood products.

Chronic Disease

A long-lasting (3 months or more) disease or condition that generally can be controlled, but not cured. Examples of chronic diseases include diabetes, high blood pressure, and asthma.

Clotting Factor

Blood contains a number of proteins, called clotting factors, which stop bleeding. People with hemophilia have low levels of either factor VIII (factor eight) or factor IX (factor nine).

Co-occurring medical conditions

The presence of one or more additional disorders or diseases that occur along with the main disease or disorder.

Clotting Factor Concentrate (“Factor”)

Factor concentrate is a concentrated mixture of the missing or defective blood clotting factor (proteins that stop bleeding) that is injected into the affected person’s vein. Factor can be used as needed when a person is bleeding or it can be used on a regular basis to prevent bleeds from occurring. There are two types of clotting factor concentrate products used to treat hemophilia: plasma-derived products and recombinant factor concentrates. Plasma-derived factor concentrates are made by separating the clotting proteins from other parts of donated blood. Recombinant factor concentrates contain clotting proteins that are produced in the laboratory using special procedures that do not require donated blood.

Genetic Condition

A condition that is caused by a difference in the genes from what is typical. Because genes are inherited from one’s parents, some genetic conditions may be passed down from one generation to the next.

Genetic Platelet Function Disorder

A condition in which platelets, the blood cells that help blood form clots, do not work the way they should because of a change in a gene. Examples of these conditions include Glanzmann thrombasthenia, Hermansky-Pudlak syndrome, and Gray platelet syndrome.

Immune Tolerance Induction (ITI)

A treatment given for the primary purpose of getting rid of an inhibitor. Factor concentrate is given regularly over a period of time until the body is trained to recognize the treatment product without reacting to it. When immune tolerance induction is successful, the inhibitors disappear and the patient’s response to factor concentrate returns to normal. (Adapted from World Federation of HemophiliaExternal)

Inherited Thrombocytopenia

A genetic condition in which individuals don’t have enough platelets in their blood. Platelets help blood form clots, which stop bleeding.

Intracranial Hemorrhage

Bleeding inside the skull.


If a person with hemophilia has a clotting factor inhibitor, it means that his immune system stops recognizing and accepting the clotting factor concentrate as a normal part of blood. The immune system thinks the factor is a foreign substance and tries to destroy it by developing and using inhibitors, a type of antibody. Antibodies are proteins that normally recognize and destroy harmful substances in the body, such as bacteria and viruses. However, inhibitors are abnormal antibodies that destroy clotting factors, thus stopping the clotting factor concentrate from working. This makes it more difficult to stop a bleeding episode. People with hemophilia who develop an inhibitor do not respond as well to treatment. There are different types of inhibitors; inhibitors most often appear during the first year of hemophilia treatment but they can appear at any time.

Inhibitor Titer

A blood test used to diagnose inhibitors. The blood test measures inhibitor levels (called inhibitor titers) in the blood. The amount of inhibitor is measured in Bethesda units (BU). The higher the number of BU, the more inhibitor is present. A “low titer” inhibitor has a low measurement, usually less than 5 BU. A “high titer” inhibitor has a high measurement, usually much higher than 5 BU.


Hemophilia is a genetic (inherited) bleeding disorder in which the blood does not clot properly due to low levels of clotting factor VIII (factor eight) or factor IX (factor nine). This can lead to spontaneous bleeding (bleeding that starts inside the body for no known reason) as well as uncontrolled bleeding following injuries or surgery. A person’s hemophilia severity is determined by the amount of clotting factor in the blood. Lower levels of clotting factor indicate more severe hemophilia.

HCV (hepatitis C virus)

The virus that causes the liver infection, Hepatitis C. The hepatitis C virus is spread through contact with blood, most commonly among people who share needles to inject illegal drugs.

HIV (human immunodeficiency virus)

HIV is a virus that infects specific cells of the immune system, called CD4 cells, or T cells. Over time, HIV can destroy so many of these cells that the body can’t fight off infections and disease. When this happens, HIV infection leads to Acquired Immunodeficiency Syndrome, or AIDS. Unlike some other viruses, the human body cannot get rid of HIV. HIV is spread from one person to another through body fluids, such as blood or semen. The risk of HIV infection through blood and blood products is very small, as a result of donor and blood screening.


A PICC line is a peripherally inserted central catheter line, which is a small tube that is inserted into a vein in the arm and threaded up the vein all the way to a large blood vessel in the chest. It may be used to give clotting factor concentrate.


Platelets are blood cells that help the blood form clots, which in turn stop a bleeding episode. They are smaller than red or white blood cells.


A device that is surgically placed under the skin of the chest and attached to a tube that is inserted directly into a large vein in the upper chest. It is used for giving clotting factor concentrates or other medications.


A treatment on a regular schedule to prevent an illness, condition, or negative health outcome. For people with a bleeding disorder, prophylaxis refers to regular infusions with factor concentrate to prevent a bleeding episode from occurring. Primary prophylaxis is usually started in young children to reduce or prevent joint disease, and it is continued indefinitely. Secondary prophylaxis is usually short term; it is started when a bleed has occurred and it is continued on a regular schedule for a defined period of time.

Von Willebrand Disease

A genetic blood disorder in which the blood does not clot properly. Blood contains many proteins that help the body stop bleeding. One of these proteins is called von Willebrand factor (VWF). People with von Willebrand disease either have a low level of VWF in their blood or the VWF protein doesn’t work the way that it should.