Anti-inhibitor coagulant complex. See APCC.

Anamnestic response:
Term used to describe a rapid production or increase in inhibitor titers following exposure to replacement therapy in a patient with previously low titers of inhibitors.

Agents that inhibit the breakdown of fibrin, such as aminocaproic acid or tranexamic acid.

Activated prothrombin complex concentrates. Also known as anti-inhibitor coagulant complex (AICC). APCCs are human plasma-derived products containing precursors and activated factors II, VII, IX, and X.

Activated partial thromboplastin time. aPTT is defined as the time needed for a fibrin clot to form in plasma to which calcium and a phospholipid reagent have been added. aPTT is used to evaluate the intrinsic clotting system.

Damage to the structures of the joint including the synovium, cartilage, and underlying bone which often results from repeated bleeding episodes and leads to pain, stiffness, and limitation in function.

Arthropathy is a term used to describe a joint affected by a disease, such as seen in hemophilia.

Bethesda Units:
A measure of inhibitor activity level. One Bethesda Unit is the quantity of antibody that will inactivate 50% factor activity when the patient’s plasma is incubated with normal plasma for 2 hours at 37 degrees centigrade.

Bleeding time. BT is usually used as an indicator of a platelet abnormality, such as thrombocytopenia or abnormal function. Although BT may be prolonged in some patients with von Willebrand disease, it is usually not affected in patients with hemophilia.

Bypassing factor products:
Coagulation factor products which bypass the coagulation pathway, usually the intrinsic system. These products supply activated or partially activated forms of coagulation factors such as X, VII, and IX.

Complete blood count. CBC measures the number of blood cells in the blood including red blood cells, white blood cells, and platelets.

Clotting factor:
Plasma proteins involved in the coagulation process.

Compartment syndrome:
A limb-threatening complication of hemophilia resulting from a soft tissue injury or hemorrhage into a compartment such as the forearm or calf. Compartment syndrome may manifest with swelling, pain, and paresthesias.

Contact factor (factors XI and XII, prekallikrein, high molecular weight kininogen):
Protein coagulation factors present in circulating blood that activate the coagulation cascade via the intrinsic pathway.

Human plasma-derived product rich in factor VIII and von Willebrand factor (vWF). Cryoprecipitate is formed after frozen human plasma is thawed and the liquid supernatant removed.

Also known as desmopressin. DDAVP is a synthetic analog of the naturally occurring hormone vasopressin. DDAVP increases plasma levels of factor VIII and von Willebrand factor, and also increases platelet adhesion and shortens the bleeding time. DDAVP has been successfully used for patients with mild hemophilia A or those with certain subtypes of von Willebrand disease.


Purplish discoloration of the skin. Ecchymosis is the result of extravasation of blood under the skin and is usually larger than petechiae.

A bleeding episode that occurs within a joint space.

A mass of clotted or partially clotted blood that is localized and confined within a space or organ.

Hemophilia A:
Usually a congenital disorder of coagulation, but may be acquired in some populations of patients. Patients with hemophilia A have a deficiency of factor VIII, a coagulation factor essential for blood coagulation.

Hemophilia B:
Usually a congenital disorder of coagulation. Patients with hemophilia B have a deficiency of factor IX, a coagulation factor needed for blood coagulation.

Hemophilia treatment centers:
See HTC.

High molecular weight kininogen:
A plasma protein that acts as a cofactor in the activation of factor XII.

High responder:
A classification of a patient with an inhibitor, based on inhibitor titers and response to challenge with the deficient coagulation factor. Patients who are considered high responders have or have had high inhibitor titers usually > 10 Bethesda units.

Hemophilia treatment center. A specialized care center, defined and recognized by the federal Office of Maternal and Child Health and the Centers for Disease Control and Prevention, for patients with hemophilia and related bleeding disorders. HTCs can provide hemophilia patients with multidisciplinary care and have been shown to improve quality of life and reduce morbidity and mortality in patients with bleeding disorders.

Idiopathic thrombocytic purpura:
See ITP.

Immune tolerance induction:
See ITI.

Antibodies produced by the body as an immune response to a coagulation factor. Inhibitors bind to the coagulation factor, preventing the factor from interacting with phospholipids during the coagulation cascade.

Immune tolerance induction. Immune tolerance induction is a program of care designed to reduce or eliminate inhibitors in patients with hemophilia. A variety of immune tolerance induction protocols exist, but usually include chronic exposure to the deficient factor against which the inhibitor is directed, plus/minus immunomodulating agents such as IVIG and cyclophosphamide.

Immune thrombocytic purpura. A condition characterized by thrombocytopenia, ecchymoses, and hemorrhage from mucosal membranes which may mimic some types of inherited bleeding disorders. ITP is an antibody mediated process, which results in removal of platelets by the reticuloendothelial system.

Liver clot:
An unstable and often large, friable clot commonly forming in mucous membranes. Liver clots usually lead to excessive bleeding and abnormal wound healing.

Low responders:
Classification of a patient with inhibitors, based on inhibitor titers and response to exposure to the deficient coagulation factor against which the antibody is directed. Patients who are considered low responders have low inhibitor titers (usually< 5 Bethesda Units) despite repeated exposure. These patients often require higher doses of replacement therapy calculated to overcome the present inhibitor titer and achieve hemostasis. Patients who are low responders may convert to high responders.

Malmรถ immune tolerance induction:
A specific immune tolerance induction protocol consisting of high dose replacement therapy, cyclophosphamide, IVIG, plus/minus extracorporeal immune adsorption.

Excessive bleeding during menses. For some women with bleeding disorders (such as von Willebrand disease), menorrhagia may be the only symptom. Women who are carriers of hemophilia may also experience menorrhagia.

Mild hemophilia:
Classification used for patients with hemophilia who have factor levels of 5% or greater of normal. Patients with mild hemophilia bleed infrequently, usually only after some type of injury/trauma or surgical intervention. The exact percentage of patients with mild hemophilia may be underestimated due to lack of identification of the entire population, but it is estimated that mild hemophilia represents about 15% to 20% of the total population.

Moderate hemophilia:
Classification used for patients with hemophilia who have factor levels of 1% to 5% of normal. Moderate hemophilia represents about 15% of patients with hemophilia A and about 30% of patients with hemophilia B. Patients with moderate hemophilia have a higher risk of bleeding than those with mild hemophilia, but usually do not experience frequent spontaneous bleeds.

On-demand therapy:
Administration of replacement factor in response to a bleeding episode.

Prothrombin complex concentrate. A human plasma-derived product containing coagulation factors II, VII, IX, and X. These concentrates may also contain activated coagulation factors.

Polymerase chain reaction. PCR is an enzymatic test used to copy and amplify two strands of DNA.

Small reddish or purple hemorrhagic spots appearing on the skin. Petechiae are much smaller than ecchymoses.

A plasma protein that, in combination with kininogen, acts as a cofactor for activation of factor XII.

Primary prophylaxis:
Administration of replacement factor on a regular schedule to prevent bleeding episodes and their subsequent sequelae usually initiated in young patients with severe hemophilia.

Prothrombin complex concentrate:
See PCC.

An uncommon complication of bleeding in patients with hemophilia. Recurrent bleeding in muscle or joints may result in the formation of an encapsulated hematoma or a pseudocyst. Pseudocysts that persist may lead to necrotic damage of adjacent structures.

Prothrombin time. PT is defined as the time needed for a clot to form in blood after the addition of thromboplastin and calcium. PT is used to evaluate the extrinsic clotting system.

Partial thromboplastin time. PTT was the precursor of aPTT. It was used to detect abnormalities in the intrinsic clotting system but was relatively insensitive to heparin.

Replacement factor:
Coagulation factor products (either human plasma-derived or recombinant) used for prophylaxis or treatment of bleeding episodes in patients with hemophilia or related bleeding disorders.

An acronym for rest, ice, compression, and elevation. These measures are recommended as adjunctive therapy to factor replacement for bleeding episodes. RICE may be used alone for chronic hemophilic arthropathy without acute bleeding or for small subcutaneous hematomas not requiring replacement factor. The goal of RICE therapy is to prevent or limit musculoskeletal damage.

An antibiotic used in the in vitro assay of von Willebrand factor (vWF). Ristocetin induces vWF binding to glycoprotein Ib receptors on platelets.

Secondary prophylaxis:
Administration of factor replacement to prevent bleeding in patients who have early arthropathy as a result of previous severe joint bleeds. Secondary prophylaxis may be administered in order to interrupt a bleeding episode or to rest a joint experiencing repeated bleeding.

Severe hemophilia:
Classification used for patients with hemophilia A or B who have factor levels of less than 1% of normal. Severe hemophilia represents about 60% of patients with hemophilia A and about 50% of patients with hemophilia B. Patients with severe hemophilia are at high risk for spontaneous bleeding, especially into the joints and muscles. These patients are also at a higher risk for life-threatening bleeds, such as CNS hemorrhage.

Inflammation of the synovial membrane within a joint resulting in pain and swelling. In patients with hemophilia, synovitis may develop after one or several bleeding episodes. If bleeding is persistent or frequent, the condition may become chronic, leading to permanent joint damage.

Progressively decreasing or diminishing response to a repeated treatment.

Target joint:
A joint that has repeated bleeding episodes, usually defined as 3 hemorrhages within a 3-month period. Target joints are more prone to have permanent damage, as the joint often develops synovitis and subsequent damage.

Vitamin K-dependent coagulation factors (factors II [prothrombin], VII, IX, X):
Coagulation factors that require vitamin K for post-translational modification. Vitamin K serves as a cofactor for the g-carboxylation of glutamic acid residues on the coagulation protein. These residues are required for calcium binding of the coagulation factor, allowing subsequent interaction with the phospholipid membrane.

von Willebrand disease:
A congenital or acquired bleeding disorder where the von Willebrand factor protein is deficient or abnormal. Von Willebrand factor is needed for platelet adherence to damaged epithelium.

vWF:ristocetin cofactor activity: A quantitative, in vitro assay of von Willebrand factor activity using ristocetin.

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