Why Get Tested?
As part of an investigation of a possible bleeding disorder or thrombotic episode; to monitor unfractionated (standard) heparin anticoagulant therapy
When to Get Tested?
When you have unexplained bleeding or blood clotting; when you are on unfractionated (standard) heparin anticoagulant therapy; sometimes as part of a pre-surgical screen
Sample Required?
A blood sample drawn by needle from a vein in the arm
How is it used?
The PTT test is used to investigate unexplained bleeding or clotting. It may be ordered along with a PT (Prothrombin Time) test to evaluate hemostasis, the process that the body uses to form blood clots to help stop bleeding. The PTT evaluates the coagulation factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen) as well as prekallikrein (PK) and high molecular weight kininogen (HK). A PT test evaluates the coagulation factors VII, X, V, II, and I (fibrinogen). By evaluating the results of the two tests together, a doctor can gain clues as to what bleeding or clotting disorder may be present.
A PTT is often used to monitor standard (unfractionated, UF) heparin anticoagulant therapy. Heparin is a drug that is given intravenously (IV) or by injection to prevent and to treat thromboemboli. When it is administered for therapeutic purposes, it must be closely monitored. If too much is given, the treated person may bleed excessively; with too little, the treated person may continue to clot.
If the PTT is prolonged and the cause is not anticoagulant therapy or heparin contamination, then a second PTT test is performed by mixing the patient's plasma with pooled normal plasma (a collection of plasma from a number of normal donors). If the PTT time returns to normal ("corrects"), it suggests a deficiency of one or more of the coagulation factors in the patient's plasma. If the time remains prolonged, then the problem may be due to the presence of an abnormal factor inhibitor (autoantibody). Further studies can then be performed to identify what factors may be deficient or determine if an inhibitor is present in the blood. Nonspecific inhibitors, such as lupus anticoagulant and anticardiolipin antibodies, are associated with clotting episodes and with recurrent miscarriages, especially those that occur in the second or third trimester. For this reason, PTT testing may be performed to help investigate recurrent miscarriages.
Based on carefully obtained patient histories, the PTT and PT tests are sometimes selectively performed as pre-surgical procedures to screen for potential bleeding tendencies.
Other testing that may be done along with a PTT includes:
Platelet counts – should always be monitored during heparin therapy to promptly detect any heparin-induced thrombocytopenia
Thrombin time testing – sometimes ordered to help rule out heparin contamination
Fibrinogen testing – may be done to rule out hypofibrinogenemia as a cause of PTT prolongation
As part of an investigation of a possible bleeding disorder or thrombotic episode; to monitor unfractionated (standard) heparin anticoagulant therapy
When to Get Tested?
When you have unexplained bleeding or blood clotting; when you are on unfractionated (standard) heparin anticoagulant therapy; sometimes as part of a pre-surgical screen
Sample Required?
A blood sample drawn by needle from a vein in the arm
How is it used?
The PTT test is used to investigate unexplained bleeding or clotting. It may be ordered along with a PT (Prothrombin Time) test to evaluate hemostasis, the process that the body uses to form blood clots to help stop bleeding. The PTT evaluates the coagulation factors XII, XI, IX, VIII, X, V, II (prothrombin), and I (fibrinogen) as well as prekallikrein (PK) and high molecular weight kininogen (HK). A PT test evaluates the coagulation factors VII, X, V, II, and I (fibrinogen). By evaluating the results of the two tests together, a doctor can gain clues as to what bleeding or clotting disorder may be present.
A PTT is often used to monitor standard (unfractionated, UF) heparin anticoagulant therapy. Heparin is a drug that is given intravenously (IV) or by injection to prevent and to treat thromboemboli. When it is administered for therapeutic purposes, it must be closely monitored. If too much is given, the treated person may bleed excessively; with too little, the treated person may continue to clot.
If the PTT is prolonged and the cause is not anticoagulant therapy or heparin contamination, then a second PTT test is performed by mixing the patient's plasma with pooled normal plasma (a collection of plasma from a number of normal donors). If the PTT time returns to normal ("corrects"), it suggests a deficiency of one or more of the coagulation factors in the patient's plasma. If the time remains prolonged, then the problem may be due to the presence of an abnormal factor inhibitor (autoantibody). Further studies can then be performed to identify what factors may be deficient or determine if an inhibitor is present in the blood. Nonspecific inhibitors, such as lupus anticoagulant and anticardiolipin antibodies, are associated with clotting episodes and with recurrent miscarriages, especially those that occur in the second or third trimester. For this reason, PTT testing may be performed to help investigate recurrent miscarriages.
Based on carefully obtained patient histories, the PTT and PT tests are sometimes selectively performed as pre-surgical procedures to screen for potential bleeding tendencies.
Other testing that may be done along with a PTT includes:
Platelet counts – should always be monitored during heparin therapy to promptly detect any heparin-induced thrombocytopenia
Thrombin time testing – sometimes ordered to help rule out heparin contamination
Fibrinogen testing – may be done to rule out hypofibrinogenemia as a cause of PTT prolongation
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