Prothrombin Time

Latest Edit: Hector 2014-03-24 (EDT)

See Also	Lab Tests

This test is used to assess the adequacy of the extrinsic system and common pathway in the clotting mechanism.

Discussion

• The hemostatic and coagulation system consists of a homeostatic balance between factors encouraging the clotting and factors encouraging clot dissolution.
• The PT measures the clotting ability of factors I (fibrinogen), II (prothrombin), V, VII, and X, which are clotting factors in the extrinsic system and coagulation pathway
• When these clotting factors exist in deficient quantities, the PT is prolonged

Patient Preparation

• No fasting required.

• Factors which can cause increased levels

• Alcohol, Diarrhea

• Drugs: Allopurinol, aminosalicylic acid, barbiturates, beta-lactam antibiotics, chloral hydrate, cephalothins, chloramphenicol, chlorpromazine (Thorazine), cholestyramine, cimetidine, clofibrate, colestipol, ethyl alcohol, glucagon, heparin, methyldopa (Aldomet), neomycin, oral anticoagulants, propylthiourcil, quinidine, quinine, salicylates, and sulfonamides

• Factors which can cause decreased levels

• A diet high in fat or leafy vegetables

• Drugs: Anabolic steroids, barbiturates, chloral hydrate, digitalis, diphenhydramine (Benadryl). estrogens, griseofulvin, oral contraceptives, and vitamin K

Clinical Implications

High levels indicate:

• Liver disease
• Hereditary factor deficiency
• Vitamin K deficiency
• Bile duct obstruction
• Coumarin ingestion
• Disseminated intravascular coagulation (DIC)

Associated Tests

• Bleeding time, Thrombin time, Partial thromboplastin time, Coagulating factor concentration