The definitions used in this glossary of terminology either have been provided by the authors of the articles, or have been extracted wholly or in part, or paraphrased from the following sources: The American Medical Association Encyclopedia of Medicine, Charles B. Clayman, MD, Medical Editor, Random House, New York, 1989; Biotechnology from A to Z, 2d Edition, William Bains, Oxford University Press, New York, New York, 2002; A Dictionary of Genetics, 6th Edition, Robert C. King and William D. Stansfield, Oxford University Press, New York, New York, 2002; Dorland's Illustrated Medical Dictionary, 29th and 30th Editions, W. B. Saunders Company, Philadelphia, 2000, 2003; Genes VII, Benjamin Lewin, Oxford University Press, New York, New York, 2000; The Gale Encyclopedia of Genetic Disorders, Volumes I and II, Stacey L. Blachford, Ed., Thomson Learning, New York, New York, 2002; The Merriam-Webster Dictionary, Merriam-Webster, Inc., Springfield, Massachusetts, 1997; Molecular Biology of the Cell, 3rd Edition, Bruce Alberts, et al., Garland Publishing, 1994; The Random House Dictionary of the English Language, Unabridged Edition, 1966; Webster's Ninth New Collegiate Dictionary, 1991.


1. Any of several substances or activities that are necessary to produce a result, e.g., a coagulation factor (see below). Often, use of the term "factor" indicates that the chemical nature of the substance or its mechanism of action is unknown, as in endocrinology, where "factors" are renamed as "hormones" when their chemical nature is determined.

2. One of two or more quantities that multiplied together form a product.

3. A gene (hereditary factor).

Antihemophilic Factor (AHF) -

1. See Factor VIII under coagulation factor (below).

2. [USP] A sterile freeze-dried powder containing the Factor VIII fraction prepared from units of human venous plasma obtained from suitable whole-blood donors; it may contain heparin sodium or sodium citrate. Used to arrest hemorrhage or to prevent hemorrhage during surgery or other procedures in patients with hemophilia A; administered intravenously.

Coagulation Factors - Substances in the blood that are essential to the clotting process and hence, to the maintenance of normal hemostasis. They are designated by Roman numerals, to which the notation "a" is added to indicate the activated state. Platelet factors (see below), designated by Arabic numerals, also play a role in coagulation.

Coagulation Factor II, prothrombin - A plasma protein that is converted to the active form thrombin (factor IIa) by cleavage by activated factor X (Xa) in the common pathway of blood coagulation; thrombin then cleaves fibrinogen to its active form fibrin. Deficiency of the factor leads to hypoprothrombinemia.

Coagulation Factor III, tissue thromboplastin - A lipoprotein functioning in the extrinsic pathway of blood coagulation, activating factor X (see below).

Coagulation Factor V, proaccelerin - A heat- and storage-labile material, present in plasma but not in serum, functioning in both the intrinsic and extrinsic pathways of blood coagulation. Deficiency of this factor, an autosomal recessive trait, leads to a rare hemorrhagic tendency, known as Owren's disease or parahemophilia, which varies greatly in severity.

Coagulation Factor VIII, antihemophilic factor (AHF) - A relatively storage-labile factor (see below) participating only in the intrinsic pathway of blood coagulation. Deficiency of this factor, when transmitted as a sex-linked recessive trait, causes classical hemophilia (hemophilia A). (See also antihemophilic factor above.)

Coagulation Factor IX, plasma thromboplastin component (PTC) - A relatively storage-stable substance involved in the intrinsic pathway of blood coagulation; upon activation, it activates factor X (see below). Deficiency results in a hemorrhagic syndrome called hemophilia B, resembling hemophilia A. Called also autoprothrombin II, Christmas factor, and antihemophilic factor B.

Coagulation Factor X, Stuart factor - A storage-stable factor that participates in both the intrinsic and extrinsic pathways of blood coagulation, uniting them to begin the common pathway of coagulation. Once activated, it forms a complex with calcium, phospholipid, and factor V (see above); the complex (prothrombinase) can cleave and activate prothrombin to thrombin. Deficiency of this factor may cause a systemic coagulation disorder.

Coagulation Factor XI, plasma thromboplastin antecedent (PTA) - A stable factor involved in the intrinsic pathway of blood coagulation; once activated, it activates factor IX. Deficiency of this factor results in a systemic blood-clotting defect called hemophilia C, which may resemble hemophilia A. Called also antihemophilic factor C.

Coagulation Factor XII, Hageman factor - A stable factor activated by contact with glass or other foreign surfaces, which initiates the intrinsic process of blood coagulation by activating factor XI and participates in activation of the kinin and fibrinolytic pathways. Deficiency of this factor results in a tendency toward thrombotic disorders, due to lack of activation of the fibrinolytic pathway. Called also glass factor, contact factor, or activation factor.

Heat-labile Factor - See Factor V under Coagulation Factors (above).

Platelet Factor - Factors important in hemostasis which are contained in or attached to the platelets.

Storage-labile Factor - A factor which shows chemically-unstable attributes during storage.

von Willebrand Factor (vWF) - The attribute of factor VIII (see above) necessary for the adhesion of platelets to vascular elements. Deficiency of this factor results in the prolonged bleeding time seen in von Willebrand's disease.

Arrow_right Used in 18 Article abstracts

Arrow_right Used in 16 Article translations