prothrombin (redirected from prothrombin deficiency)

prothrombin /pro·throm·bin/ (pro-throm´bin) coagulation factor II.

---

pro·throm·bin (pr-thrmbn)

n.

A glycoprotein formed by and stored in the liver and present in the blood plasma that is converted to thrombin in the presence of thromboplastin and calcium ion during blood clotting. Also called factor II.

---

Prothrombin

Prothrombin is a blood-clotting protein. Injury to a blood vessel produces a signal which triggers the conversion of prothrombin to thrombin. Thrombin is a protein which plays a central role in provoking the assembly of other proteins to form the blood clot.

Mentioned in: Fibrinogen Test, Prothrombin Time, Vitamin K Deficiency

---

prothrombin,

a plasma protein that is converted to the active form, factor IIa, or thrombin, by cleavage. Thrombin then cleaves fibrinogen to its active form, fibrin. Factor II deficiency leads to hypoprothrombinemia. Also called factor II.

---

prothrombin (prōthrom´bin),

n a glycoprotein precursor of thrombin that is produced in the liver and is necessary for the coagulation of blood. A prothrombin deficiency is uncommon but may occur in liver disease. Vitamin K is essential for the synthesis of prothrombin.

prothrombin, B,

n See factor II.

prothrombin, component A of,

n See factor V.

prothrombin, component B of,

n See factor VII.

prothrombin time,

n a one-stage test for detecting certain plasma coagulation defects caused by a deficiency of factors V, VII, or X. Thromboplastin and calcium are added to a sample of the patient's plasma and, simultaneously, to a sample from a normal control. The amount of time required for clot formation in both samples is observed. A prolonged prothrombin time indicates deficiency in one of the factors. Normal findings are 11 to 12.5 seconds.

---

prothrombin

a glycoprotein present in the plasma that is converted into thrombin by extrinsic thromboplastin during the second stage of blood clotting; called also clotting factor II.

---

prothrombin consumption test

determines thromboplastin generating capacity, which provides information about the first stage of coagulation. When clotting of a normal blood sample occurs, prothrombin is converted to thrombin, thus there should be little or no prothrombin in the serum after the clot is formed. If, however, there is deficiency of blood coagulation, some of the prothrombin will not be utilized (consumed). Abnormal results of the test are found in deficiencies of the first-stage factors of coagulation (factors VIII and IX), and in the presence of circulating anticoagulants, thrombocytopenia, and any other condition leading to inadequate generation of thromboplastin. Called also serum clot time.

prothrombin converting activity

the step in blood coagulation in which factor Xa, together with factor V react with phospholipid in the presence of calcium, activates prothrombin to form thrombin.

prothrombin deficiency

see hypoprothrombinemia.

prothrombin time test

a test to measure the activity of clotting factors V, VII and X, prothrombin and fibrinogen. Deficiency of any of these factors leads to a prolongation of the one-stage prothrombin times, as will circulating anticoagulants that are active against factors V, VII, or against thromboplastin. Called also pro-time.

The one-stage (OSPT) test is performed by measuring the time required for clot formation after tissue extract and calcium are added to citrated plasma. Called also Quick's prothrombin test. A two-stage test determines plasma levels of prothrombin by finding the dilution of plasma that clots a standard fibrinogen reagent in a set period of time.