Glossary of Blood Clot and Clotting Disorder Terms

Activated Partial Thromboplastin Time (aPTT )… A blood test that measures the length of time (in seconds) that it takes for clotting to occur when certain substances are added to the liquid portion of blood in a test tube. It is used to detect clotting factor deficiencies and to monitor heparin’s effectiveness. Learn More..

Anticoagulant … medications, commonly referred to as “blood thinners,” that lengthen the time it takes for blood to clot, rather than actually “thinning the blood.” They are used to prevent or to treat blood clots, and may be injected either into a vein or under the skin (e.g., heparin, low-molecular-weight heparins), or taken by mouth (warfarin/Coumadin®).   Learn More..

Antiphospholipid Antibody Syndrome (APS) … This rare autoimmune disorder is characterized by recurrent blood clots and/or miscarriages in which there is an elevated antiphospholipid antibody level in the blood. APS may occur in those with lupus or related autoimmune diseases. It may also occur as a primary syndrome (Primary ABS) in otherwise healthy individuals. Learn More…

Antiphospholipid Antibody … This antibody, which is directed against one’s own tissues (autoantibody), is associated with an increased risk for forming blood clots and/or recurrent miscarriages. Learn More…

Antithrombin III… A protein found in our bloodstream that controls our clotting mechanism and prevents excessive clotting. It functions as a naturally occurring mild blood thinner.  Learn More…

Antithrombin III Deficiency (AT-III)… AT-III deficiency is a disorder that increases the risk for blood clots. It can be (a) acquired, or (b) inherited, or (c) based on a misinterpretation of lab tests (values can be temporarily low at the time of the acute clot or during heparin therapy).  Learn More…

Artery… Any of the blood vessels that carry blood away from the heart and to the various parts of the body.

Arterial Blood Gas (ABG) … A technique used primarily to measure the oxygen level of the blood with precision.

Atrial Fibrillation … An abnormal rhythm or heartbeat pattern involving the atria or upper chambers of the heart. It can interrupt the normal flow of blood through the heart, allowing clots to form. These clots can potentially travel through the arteries, lodge in the brain and cause strokes. Learn More…

Blood Clot … Blood that has been converted from a liquid to a solid state. Also called a thrombus.  Learn More…

Budd Chairi Syndrome… Thrombosis of the (hepatic) veins coming from the liver, usually presenting  with abdominal pain, enlargement of the liver and fluid in the abdomen.  Learn More…

CDC… government healthcare agency, located in Atlanta, GA, whose mission is to collaborate to create the expertise, information, and the tools that people and communities need to protect their health-through health promotion, prevention of disease, injury and disability, and preparedness for new health threats.  Learn More…

Clotting Disorders… term used to describe a group of inherited or acquired conditions in which there is an increased tendency for blood to clot.  They are also called thrombophilias.  Learn More…

Chronic Thromboembolic Pulmonary Hypertension (CTEPH)… High blood pressure in the lungs that occurs in a small percentage of those who have had pulmonary embolism. The problem usually progresses but may be cured with surgery.

Coagulation… complex process by which clots form in the blood.

Coagulometer… A device used to measure the INR for warfarin monitoring.

Coumadin®… brand name for warfarin, an anticoagulant (“blood thinner”).

Deep Vein Thrombosis (DVT)… blood clot that forms in the deep veins of the legs, pelvis or arms, although it occurs most often in the legs.  Signs and symptoms include swelling, usually in one leg, leg pain or tenderness, reddish or bluish skin discoloration, and leg warm to touch.  A DVT may break off and travel to other parts of the body, most commonly the lungs as a pulmonary embolism (PE).

D-Dimers… A breakdown product of fibrin, a substance present in a blood clot. D-dimers are not generally present in the blood unless a clot has begun to form. However, the presence of D-Dimers does not guarantee that a clot is present. If D-dimers are absent, it is very unlikely that a clot has begun to form.

Duplex Ultrasound… This method combines two kinds of ultrasound. The conventional ultrasound shows the structure of blood vessels and the Doppler ultrasound shows the movement of red blood cells through the vessels. It produces images that can be color coded to show physicians where blood flow is severely blocked as well as the speed and direction of blood flow.

Economy Class Syndrome… The occurrence of deep vein thrombosis (DVT) in airline travelers due to cramped conditions compounded by inactivity, especially on long haul flights.  The term was first coined in the late 1980’s when it was observed that people who had traveled long distances by plane were at an increased risk for blood clots, especially DVT, resulting often in a pulmonary embolism. Learn More…

Endothelium… The lining of a blood vessel. A patient is more susceptible to a blood clot when the endothelium is damaged from trauma or a previous blood clot.

Factor V deficiency… An inherited bleeding disorder in which the clotting factor V (five) is low. The disorder is very rare, occurring in only 1 in 1,000,000 people. This is not the same as factor V Leiden.

Factor V Leiden (FVL)… An inherited blood clotting disorder that is found in 5% of Caucasian Americans and 1.2% of African-Americans. One can be heterozygous (have one abnormal gene), homozygous (have two abnormal genes) or normal (not have any abnormal genes). The genetic test for factor V Leiden has been available since 1994.

Fibrin… This is a solid substance (formed from fibrinogen) that makes a clot harder to break up. It forms the mesh or net that holds platelets in place.

Fibrinogen… A specialized protein or clotting factor found in blood. When a blood vessel is injured, thrombin, another clotting factor, is activated and changes fibrinogen to fibrin.

Fitted Elastic Compression Stockings…These provide counter-pressure to veins and help return fluid that has leaked out back into circulation. Ideally, they exert a pressure of at least 30 to 40 mm Hg at the ankle with less pressure at the knee.

Fresh Frozen Plasma… This is used to reverse warfarin by replacing clotting factors.

Genetic Counseling… the process of helping people understand and adapt to the medical, psychological and familial implications of genetic contributions to disease. It includes interpreting family and medical histories to assess the chance of disease occurring or recurring; educating about inherited risk, testing, management, prevention, resources and research; and counseling to promote informed choices and adaptation to the risk or condition.

Hematologist… physician who specializes in the treatment of blood diseases and disorders.  Many combine hematology with oncology (cancer specialist) and treat cancer and blood diseases.

Heparin…  an anticoagulant medicine (“blood thinner) used to treat blood clots, most often during hospitalization.

Heterozygous… Having one abnormal gene. If you are heterozygote for factor V Leiden, you have inherited the trait from one parent.

Homocysteine… An amino acid found in the blood. High homocysteine levels are a risk factor for blood clots in the veins (DVT, PE) or arteries (heart attack, stroke), and hardening of the arteries (atherosclerosis).

Hypercoaguable…an abnormally increased tendency to form blood clots, due to an inherited or acquired disorder.

Hyperhomocysteinemia… condition when homocysteine levels are abnormally elevated in the blood that may damage the lining of blood vessels and lead to the formation of blood clots. MTHFR mutation has been associated with an increased risk for hyperhomocysteinemia

Homocystinuria… A rare hereditary disease due to a deficiency of an enzyme needed to prevent the buildup of homocysteine in the blood.

Homozygous… Having two abnormal genes. If you are homozygote for factor V Leiden, you inherited an abnormal gene from both parents.

INR (International Normalized Ratio)… blood test that monitors whether the therapeutic or beneficial effect of anticoagulation is within normal range, usually between 2.0 and 3.0. It is calculated from the prothrombin time (PT), or the time it takes for blood to clot in a test tube.  INR can be monitored by a lab, or done by selected patients at home with a self-testing device. 

Low Molecular Weight Heparin (LMWH)… A form of heparin (“blood thinner”) that is injected right below the skin.  LMWHs’ effects last longer and are more predictable, require less monitoring, and generally have fewer side effects than standard heparin. LMWHs are often used as an alternative to heparin or as “bridging” therapy for patients on oral anticoagulants such as warfarin/Coumadin®. Examples of brand LMWHs are Fragmin®, Lovenox®, and Innohep®.

Lupus Anticoagulant… A type of antiphospholipid antibody associated with an increased risk for blood clots.

Lysis… The process by which a clot is dissolved or destroyed. It can occur naturally over time or be accomplished by clot-busting drugs.

Lytic therapy… A clot-busting medication given in the hospital into the blood vessel to break up clots. The treatment has a risk of bleeding. Drug names are tPA, streptokinase, and urokinase.

Magnetic Resonance Imaging (MRI)… A test that images clots in the body. While MRI does a better job of imaging the veins in the pelvis, abdomen and chest than ultrasound, ultrasound for the legs is generally adequate.

MTHFR… Stands for Methylene-Tetra-Hydro-Folate-Reductase. Some individuals with the homozygous MTHFR mutation have elevated homocysteine levels. Elevated homocysteine levels are a risk factor for blood clots. The individuals with MTHFR mutations who have normal homocysteine levels are not at increased risk for clots. Thus, the MTHFR mutation by itself is not a clotting disorder.

Myocardial Infarction… Heart attack. The death of an area of heart muscle.

Plasma… The liquid portion of blood that contains the clotting factors.

Plasminogen… A substance naturally produced by the body that helps  break down blood clots.

Platelets… Small particles in the blood that control bleeding; they form clusters to plug small holes in blood vessels and assist in the clotting process.

Polycythemia… The presence of too many red blood cells, which, if severe, may predispose a patient to DVT.

Post-Thrombotic Syndrome (PTS)/Post-Phlebitic Syndrome … complication of deep vein thrombosis (DVT). Signs and symptoms of PTS range from leg pain and/or heaviness with occasional swelling to extreme chronic pain, persistent swelling and skin color and texture changes. The extreme, most severe symptoms associated with PTS are the development of chronic leg ulcers or open wounds that are difficult to heal.

Protein C Deficiency… Protein C deficiency is an uncommon clotting disorder: approximately 1 per 700 people has inherited protein C deficiency. Since we all have two genes for every protein (one from mother and one from father), people can have two normal genes (healthy), one mutated protein C gene (heterozygous), or two mutated genes (homozygous). Individuals with protein C deficiency are typically heterozygous. Homozygous individuals have such a severe clotting problem, that they typically die immediately after birth because of clotting everywhere; this is termed Purpura fulminans.

Protein C deficiency can be caused by more than 100 different mutations in the protein C gene. This makes genetic testing for the defect very difficult, time-consuming, and expensive; it is therefore not done in routine clinical practice. A few academic institutions with a special interest in protein C deficiency perform genetic testing for research purposes. In some people protein C deficiency is due to acquired (non-inherited) causes, and may be temporary.

Protein S Deficiency… Protein S deficiency is an uncommon clotting disorder: approximately 1 per 500 to 1 per 3,000 people has inherited protein S deficiency. Since we all have two genes for every protein (one from mother and one from father), people can have two normal genes (healthy), one mutated protein S gene (heterozygous), or two mutated genes (homozygous). Individuals with protein S deficiency are typically heterozygous. Homozygous individuals have such a severe clotting problem, that they typically die immediately after birth because of clotting everywhere; this is termed Purpura fulminans.

Protein S deficiency can be caused by more than 100 different mutations in the protein S gene. This makes genetic testing for the defect very difficult, time-consuming, and expensive; it is therefore not done in routine clinical practice. A few academic institutions with a special interest in protein S deficiency perform genetic testing for research purposes. In some people protein S deficiency is due to acquired (non-inherited) causes, and may be temporary.

Prothrombin Deficiency… Prothrombin (= factor II) is 1 of the approximately 15 clotting proteins that is needed to stop us from bleeding. If you are low in prothrombin, you have a tendency to bleed.

Prothrombin 20210 mutation… The prothrombin 20210 mutation (= factor II 20210 mutation) is a very common mutation and is a mild risk factor for deep vein thrombosis (DVT) and pulmonary embolism (PE).G20210A?

blood test that measures the time (in seconds) it takes blood to clot. This provides a control for long-term oral anticoagulant therapy.  It is the basis to calculate INR. )… The prothrombin time test, also called PT, helps measure how well blood is able to clot. The test provides a control for long-term anticoagulant therapy that usually involves the use of warfarin. It is also known as INR or Protime.

Prothrombin Time (PT)…  A blood test that measures the length of time (in seconds) that it takes for clotting to occur when certain substances are added to the liquid portion of blood in a test tube. It is used to detect clotting factor deficiencies and to monitor heparin’s effectiveness.

Pulmonary Angiogram…The most definitive test to diagnose PE, this is an invasive test requiring injection of a dye through a catheter (IV line) into the body.

Pulmonary Embolism (PE)… blood clot in the lungs, a serious complication of a deep vein thrombosis (DVT).  Signs and symptoms include sudden shortness of breath, chest pain that is sharp or stabbing that may get worse with a deep breath, rapid heart rate, and/or unexplained cough, sometimes with bloody  mucus. Pulmonary embolism may be fatal in about 1 out of 3 people.

Pulmonary Infarction… The death of a small area of lung resulting from pulmonary embolism. It occurs in a small, dead-end pulmonary artery and often causes pain in the back or chest.

Pulse Oximetry… A noninvasive (no blood needed) method used to monitor the percentage of hemoglobin that is saturated with oxygen.

Spontaneous DVT… A clot that forms when there are no identified risk factors. Of those who develop a spontaneous DVT, 20-40% have an inherited or acquired predisposition to thrombosis or thrombophilia.

Stroke… A condition that occurs when oxygen-rich blood is prevented from reaching an area of the brain; it can lead to death of brain cells in that area.

Superficial Thrombophlebitis… Also called superficial vein thrombosis, this is when a blood clot or clots form in veins nearer to the surface.

Tissue Factor… A protein exposed to the blood when a blood vessel is injured. The tissue factor sets off a chain reaction – the coagulation cascade – that activates a series of clotting factors.

Thrombin… The clotting factor that converts fibrinogen to fibrin.

Thrombocytopenia … A low platelet count.

Thrombocytosis (Thrombocythemia) … Too many platelets in the blood. It may predispose a patient to thrombosis.

Thrombophilia … hereditary or acquired predisposition to develop blood clots. It is also referred to as hypercoagulable state or hypercoagulability.

Thrombosis (aka thrombus) … blood clot that forms within a blood vessel.

Thrombus … medical term for a blood clot.

Transient Ischemic Attack (TIA)… Often called a “mini stroke” but transient (short term) in nature–symptoms last less than 48 hours.

Vena Cava… A very large vein that returns blood from organs and extremities to the right side of the heart.

Vena Caval Filter… A device inserted to prevent PE in patients with DVT and/or PE when anticoagulants fail or cannot be used.

Venography/Venogram… An X-ray that takes pictures of blood flow through the veins in a certain area of the body. During the test, a special dye (contrast material) is put into the veins so they can be seen clearly on an X-ray picture.

Venous thromboembolism (VTE)… collective “umbrella” term for deep vein thrombosis (DVT) and pulmonary embolism (PE).

Vitamin K… A vitamin essential to the production of the active forms of clotting factors II, VII, IX and X in the liver.

Virchow’s Triad… The 3 factors identified with the development of blood clots: blood vessel injury, interruption of blood flow and thrombophilia (the increased tendency toward blood clotting).

Ventilation-Perfusion Scan (VQ Scan)… A test used to evaluate both air  flow (Ventilation/V) and blood flow (Perfusion/Q) in the lungs to determine whether a person has experienced a pulmonary embolism.

Warfarin… oral anticoagulant or “blood thinning” medicine. Brand name: Coumadin®

This glossary has been adapted from “100 Questions & Answers about Deep Vein Thrombosis and Pulmonary Embolism” by Audra H. James, MD, Thomas L. Ortel, MD, PhD, and Victor F. Tapson, MD, Copyright © 2008, Jones and Barlett Publishers, Sudbury, MA.

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