Hemophilia Glossary

The hemophilia glossary contains terms and definitions related to hemophilia and other bleeding disorders.   Please submit and corrections or suggestions using our Contact Form.


Not normal. Deviating from the usual structure, position, condition, or behavior. In referring to a growth, abnormal may mean that it is cancerous or premalignant (likely to become cancer).


A pain reliever and fever reducer. Brand name (Tylenol). The exact mechanism of action of acetaminophen is not known. Acetaminophen relieves pain by elevating the pain threshold (that is, by requiring a greater amount of pain to develop before it is felt by a person). Acetaminophen reduces fever through its action on the heat-regulating center (the "thermostat") of the brain. Generic is available.

Aids (Acquired Immune Deficiency Syndrome)

A disease that attacks and destroys the body’s immune system, leaving the patient extremely vulnerable to infections and other diseases.


Procedure used in prenatal diagnosis to obtain amniotic fluid which can be used for genetic and other diagnostic tests. Informally called an "amnio."


Abnormally low total volume of blood or low levels of hemoglobin, the protein that carries oxygen and carbon dioxide, or red blood cells in the blood.


A protein made by blood cells. It attacks substances that the body thinks present a danger. Inhibitors that attack replacement therapies for hemophilia are called antibodies.


The surgical joining or fusion of a joint.


Any joint disease.


Joint replacement surgery.


A very thin tube with a light at the end that is inserted into the joint through a small cut in the skin.


A surgical procedure to examine the inside of a joint.


A good example of a tradename that entered into the language, Aspirin was once the Bayer trademark for acetylsalicylic acid.
Asymptomatic    Showing no outward signs of a condition.


Any of the non-sex chromosomes.
Bethesda Inhibitor Assay     A test performed in the lab that measures the strength or titer of an inhibitor.

Bethesda Titer

Concentration or strength of a substance, such as an inhibitor, using Bethesda units.

Bethesda Units (BUS)

Units used to measure inhibitor levels, also called titers.


A collection of blood in an area. It is a term used by people with bleeding disorders to describe their bleeding episodes.

Bleeding Disorders

A group of conditions in which a person’s body cannot properly develop a clot, causing an increased chance of bleeding.

Blood Clot

Blood that has been converted from a liquid to a solid state. Also called a thrombus.

Blood In The Urine

Blood in the urine is termed hematuria.

Bypassing Agents

Agents or products that stimulate the blood clotting process by bypassing the deficient factor with a clotting factor that Occurs later in the cascade.


An individual who possesses the gene for a condition, such as hemophilia, but does not necessarily have the condition.


A sequence of successive activation reactions involving enzymes (enzyme cascade) or hormones (hormone cascade) characterized by a series of amplifications of an initial stimulus. In blood coagulation, for example, each enzyme activates the next until the final product, the fibrin clot, is reached.

Chorionic Villus Sampling

A procedure for first-trimester prenatal diagnosis. Chorionic villus sampling may be done between the eighth and tenth weeks of pregnancy. The aim is to diagnose severe abnormalities afflicting the fetus. In the procedure, tissue is withdrawn from the villi (vascular fingers) of the chorion, a part of the placenta, and examined. Chorionic villus sampling is referred to commonly as CVS.


A visible carrier of the genetic information.


The microscopically visible carriers of the genetic material. They are composed of deoxyribonucleic acid (DNA) and proteins and, under a microscope, look like little rods.


This important term in medicine comes from the Greek chronos, time and means lasting a long time.

Chronic Synovitis

Persistent, painful swelling of the tissue lining the joint.

Clotting Factor

The proteins that circulate in the blood and are needed for normal coagulation.

Clotting Factors

Blood proteins required for blood to clot normally, often called "factors."


In medicine, the clotting of blood. The process by which the blood clots to form solid masses, or clots.

Coagulation Disorders

A large group of disorders in which a person experiences excessive bleeding or alternatively, clotting.


A concentrated form of plasma that contains factor VIII.

Desmopressin Acetate

A drug used to treat mild hemophilia A and von Willebrand disease that doubles or triples factor VIII levels in the blood.


A protective membrane where a needle is inserted into a port.

DNA Deoxyribonucleic acid

One of two types of molecules that encode genetic information. (The other is RNA. In humans DNA is the genetic material; RNA is transcribed from it. In some other organisms, RNA is the genetic material and, in reverse fashion, the DNA is transcribed from it.)


A protein in the blood that helps form blood clots.

Factor Deficiencies

These are conditions identified by the particular missing clotting factor a person’s body produces. These conditions include: Factor I, II, V, VII, VIII, IX, X, XI, XII, and XIII.

Factor Replacement Therapy

In hemophilia, the infusion of clotting factor to serve as a temporary substitute for the body's missing or deficient factor. In hemophilia A, Factor VIII is infused as the replacement therapy.

Factor VIII

Factor eight, a key factor in the process of blood coagulation (clotting). Lack of normal factor VIII causes hemophilia (hemophilia A).


The protein formed during normal blood clotting that is the essence of the clot.


A surgical procedure in which a joint is removed and the cut ends of the bones are held together with screws or clamps. Fusion relieves the pain of advanced joint disease and strengthens weak joints.


A section of DNA, the code of the body that controls production of a protein.

Gene Therapy

A method of supplementing, manipulating or replacing a dysfunctional gene with a healthy functioning one. This amazing technique is currently being researched in several inherited diseases, including hemophilia. There is hope that gene therapy will lead to better treatments, and eventually cures for these diseases.


Having to do with genes and genetic information.

Genetic Testing

Tests done for clinical genetic purposes. Genetic tests may be done for diverse purposes pertaining to clinical genetics, including the diagnosis of genetic disease in children and adults; the identification of future disease risks; the prediction of drug responses; and the detection of risks of disease to future children.


Blood in a joint.


A physician who specializes in blood disorders.


An abnormal localized collection of blood in which the blood is usually clotted or partially clotted and is usually situated within an organ or a soft tissue space, such as within a muscle.


Blood in the urine. Hematuria may or may not be accompanied by pain, but it is always abnormal and should be further investigated. Painful hematuria can be caused by a number of disorders, including infections and stones in the urinary tract. Painless hematuria can also be due to many causes, including cancer.


Having only a single copy of a gene instead of the customary two copies. All of the gene on the single X chromosome in the male are in the hemizygous state.


Hemophilia is an inherited bleeding disorder

Hemophilia A

A bleeding disorder caused by a lack of Factor VIII. It is sometimes called classic or standard hemophilia.

Hemophilia B

A deficiency or absence of factor IX. It has also been called “Christmas Disease,” after the first patient that was identified with the disease.

Hemophilia Treatment Center (HTC)

A federally funded clinic where a team of doctors, nurses, social workers, and physical therapists work together to deliver comprehensive care to people with bleeding disorders.


Bleeding or the abnormal flow of blood.


A blood thinner that stops blood clots from forming.


A disease caused by injury or infection of the liver.

Hepatitis B

Inflammation of the liver due to the hepatitis B virus (HBV), once thought to be passed only through blood products. It is now known that hepatitis B can also be transmitted via needle sticks, body piercing and tattooing using un sterilized instruments, the dialysis process, sexual and even less intimate close contact, and childbirth. Symptoms include fatigue, jaundice, nausea, vomiting, dark urine, light stools. Diagnosis is by blood test. Treatment is via anti-viral drugs and/or hepatitis B immunoglobulin (HBIG).

Hereditary Disease

A condition that is genetically passed down from parent to child.


Possessing two different forms of a particular gene, one inherited from each parent. A person who is heterozygous is called a heterozygote or a gene carrier.

High Responder

A person whose inhibitor rises to a very high level after receiving factor replacement therapy.

High-Titer Inhibitor

An inhibitor that is very aggressive.


Acronym for the Human Immunodeficiency Virus, the cause of AIDS (acquired immunodeficiency syndrome). HIV has also been called the human lymphotropic virus type III, the lymphadenopathy-associated virus and the lymphadenopathy virus. No matter what name is applied, it is a retrovirus. (A retrovirus has an RNA genome and a reverse transcriptase enzyme. Using the reverse transcriptase, the virus uses its RNA as a template for making complementary DNA which can integrate into the DNA of the host organism).


A non-steroidal anti-inflammatory drug (NSAID) commonly used to treat pain, swelling, and fever. Common brand names for Ibuprofen include Advil, Motrin, and Nuprin.


rotected against infection. The Latin immunis means free, exempt.

Immune Response

Any reaction by the immune system.

Immune System

A mechanism within the body used to protect itself from harmful substances.

Immune Tolerance

A state of unresponsiveness to a specific antigen or group of antigens to which a person is normally responsive. Immune tolerance is achieved under conditions that suppress the immune reaction and is not just the absence of a immune response.

Immune Tolerance Induction (ITI)

Therapy that tries to get rid of inhibitors. It involves regular (maybe daily) infusions of high doses of specific factor. If successful, it reduces the immune system's response to the factor. That means the body does not create antibodies to the factor. ITI is also called ITT or immune tolerance therapy.

Immune Tolerance Therapy (ITT)

See immune tolerance induction (ITI).

Infuse (Poke)

To inject medicine directly into a vein using a needle and syringe.


A means of delivering treatment to people with bleeding disorders intravenously. This method is used to introduce clotting factor concentrate directly into a vein where it can go to work immediately.


ot something that is contained in a will, but rather a gene, chromosome or genome that is transmitted from parent to child.


An antibody that develops as a result of infused clotting factor concentrates. As a result of this rare complication, standard treatment temporarily doesn't work.

Joint Bleeds

Bleeding into joints that can cause joint disease and is treated by infusion of clotting factor. Joint bleeds can occur even when the joint is not injured.

Joint Health

The proper working of a joint. Infusing quickly after joint injuries and getting regular physical activity help improve joint health.

Low Responder

A person whose inhibitor level rises only slightly after receiving factor replacement therapy.

Low-Titer Inhibitor

An inhibitor that is not very aggressive.

Mild Hemophilia

A categorical term used to describe someone with a factor VIII or IX level ranging from 5% to 40% of normal blood levels of factor.

Moderate Hemophilia

A categorical term used to describe someone with a factor VIII or IX level ranging from 1% to 5% of normal blood levels of factor.


A non-steroidal anti-inflammatory drug (NSAID) used for the management of mild to moderate pain, fever, and inflammation. Naproxen blocks the enzyme cyclooxygenase that makes prostaglandins, resulting in lower concentrations of prostaglandins. As a consequence, inflammation, pain and fever are reduced. Brand names for naproxen include Anaprox, Naprelan, Naprosyn, and Aleve.


Having to do with the bones.


The liquid part of blood.


An irregular, disc-shaped element in the blood that assists in blood clotting. During normal blood clotting, the platelets clump together (aggregate). Although platelets are often classed as blood cells, they are actually fragments of large bone marrow cells called megakaryocytes.


An implanted access device through which factor may be infused.

Prophylaxis Or "Prophy"

A regular treatment regimen that prevents bleeding episodes among people with hemophilia. The word comes from the Greek for "an advance guard," an apt term for a measure taken to fend off a disease or another unwanted consequence.


A large molecule composed of one or more chains of amino acids in a specific order determined by the base sequence of nucleotides in the DNA coding for the protein.


A coagulation (clotting) factor that is needed for the normal clotting of blood. A cascade of biochemical events leads to the formation of the final clot. In this cascade, prothrombin is a precursor to thrombin.


A person with a new combination of genes, a combination of genes not present in either parent, due to parental recombination of those genes.

Recombinant Technologies

Laboratory methods of producing human proteins that do not use blood or plasma.

Severe Hemophilia

A categorical term used to describe someone with a factor VIII or IX level below 1% of normal blood levels of factor.

Spontaneous Mutation

The development of a hereditary disease such as hemophilia where there is no family history of the disease.
Spontaneously     Something that happens without a cause.


The surgical or chemical removal of the joint lining.


The tissue lining a joint. Often the place where joint bleeds start.

Target Joint

A particular joint that has experienced repeated bleeds or at least four bleeds into one joint within a six month period.

Thrombotic Events

Happen when veins or arteries become blocked by platelets that are working to "plug" an injury. This prevents blood from flowing normally through the body.


See Bethesda titer.


The transfer of blood or blood products from one person (the donor) into another person (the recipient's) bloodstream. In most situations, this is done as a lifesaving maneuver to replace blood cells or blood products lost through severe bleeding. Transfusion of your own blood (autologous) is the safest method but requires planning ahead and not all patients are eligible. Directed donor blood allows the patient to receive blood from known donors. Volunteer donor blood is usually most readily available and, when properly tested has a low incidence of adverse events.


A blood vessel that carries blood low in oxygen content from the body back to the heart. The deoxygenated form of hemoglobin (deoxyhemoglobin) in venous blood makes it appear dark. Veins are part of the afferent wing of the circulatory system which returns blood to the heart.

Viral Inactivation

Methods that kill viruses in clotting factors.

Von Willebrand Disease

A bleeding disorder in which von Willebrand factor, a protein that works with factor VIII, is missing or does not function normally. von Willebrand disease affects both females and males.

X Chromosome

A sex chromosome found in both females and males. Normal females usually have two X chromosomes. Normal males usually have one X along with a Y chromosome. The complete chromosome complement consisting of 46 chromosomes is conventionally written as 46,XX for females and 46,XY for males.


On the X chromosome. "Linked" in genetics does not mean merely associated. An X-linked gene travels with the X chromosome and therefore is part of the X chromosome.