Activated Partial Thromboplastin Time APTT
PTT Test/PT with INR Test, APTT, and aPTT, Partial Thromboplastin Time, PTT
Why do you need to get tested?
- Unexplained bleeding or easy bruising
- A blood clot in a vein or artery
- An acute condition such as disseminated intravascular coagulation (DIC) may cause both bleeding and clotting as coagulation factors are used up at a rapid rate.
- A chronic condition such as liver disease that may affect clotting The doctor orders an aPTT when
- As part of an investigation into lupus anticoagulant, anticardiolipin antibodies, and antiphospholipid syndrome
- The patient has had a blood clot
- A woman has had recurrent miscarriages
- The patient has switched from heparin therapy to longer-term warfarin (Coumadin®) therapy, the two are overlapped, and both the PTT and PT are monitored until the patient has stabilized.
- The patient has a scheduled surgical operation. He or she may have a PTT prior to surgery when the surgery carries an increased risk of blood loss.
- If the patient has a clinical history of bleeding, such as frequent or excessive nose bleeds and easy bruising, which may indicate the presence of a bleeding disorder.
- 1. Underlying conditions that lead to lower levels of clotting factors:
- Liver disease—The liver produces the most coagulation factors. Therefore, liver disease may lead to prolonged PT and PTT. However, PT is more likely to be prolonged than PTT.
- Vitamin K deficiency—Vitamin K is crucial for the formation of several clotting factors. While Vitamin K deficiencies are not common, they can occur due to an extremely poor diet, malabsorption disorders, or prolonged use of certain antibiotics, for example. PT is more likely to be prolonged than is PTT.
- 2. Less commonly inherited clotting factor deficiencies:
- Von Willebrand disease (vWD) is the most common inherited bleeding disorder. The disease impacts platelet function due to decreased von Willebrand factor. PTT is normal in most cases of vWD but can be prolonged in severe vWD.
- Hemophilia A and hemophilia B (Christmas disease) are two other inherited bleeding disorders resulting from a decrease in factors VIII and IX, respectively.
- Deficiencies of other coagulation factors, like factors XII and XI. Deficiency in XI can cause abnormal bleeding, but deficiency of XII is not associated with bleeding risk in the body.
- 3. Inhibitors that impact results:
- Lupus anticoagulant, a non-specific inhibitor, is an autoantibody (antiphospholipid antibody) that interferes with the aPTT by targeting substances called phospholipids that are used in the aPTT. Lupus anticoagulants can prolong the aPTT result.
- Some specific inhibitors may impact results. These are relatively rare. Specific inhibitors are antibodies that specifically target certain coagulation factors (known as factor-specific inhibitors), affecting how they function, such as antibodies that target factor VIII. Factor-specific inhibitors can lead to heavy bleeding.
- Heparin—is an anticoagulant and will prolong an aPTT either as part of a sample or treatment.
- Warfarin anticoagulation therapy may prolong the aPTT. The prothrombin time/international normalized ratio is used to monitor warfarin therapy.
Frequently ordered together
COAGULATION FACTOR II ACTIVITY
COAGULATION FACTOR V ACTIVITY
COAGULATION FACTOR VII ACTIVITY
FACTOR VIII ACTIVITY
COAGULATION FACTOR X ACTIVITY
INTRINSIC FACTOR AB
LUPUS ANTICOAGULANT WITH REFLEX
VON WILLEBRAND SCR
FACTOR IX AG
Von Willebrand Factor Antigen
Thrombin Clotting Time with Reflex to Mixing Studies
Prothrombin Time with INR
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