This small reduction occurs because the plasma is being diluted with normal plasma, but if the level does not correct into the reference range, the PTT is considered inhibited.
There are 3 broad categories of inhibitors. Drugs that can act as inhibitors include heparin and direct thrombin inhibitors, such as lepirudin, argatroban, and the oral agent dabigatran.
An inhibited PTT can also be due to the presence of inhibitors directed against blood clotting factors that result in bleeding disorders, most commonly factor VIII.
Spontaneous development of an inhibitor against factor VIII, also called autoimmune hemophilia A, is a potentially life-threatening acquired bleeding disorder. The third category of inhibitors is called nonspecific inhibitors , an example of which is lupus anticoagulants. Although lupus anticoagulants are not necessarily risk factors for bleeding, they can be risk factors for thrombosis, either venous or arterial. In some patients, the presence of one specific factor deficiency—such as factor XII deficiency—does not indicate a bleeding disorder.
Factor XII is not necessarily important for clot formation. Therefore, a long PTT is not necessarily a simple problem; it could reflect a variety of underlying disorders. If the results are abnormal, further testing is needed. Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain.
Afterward, the site may be sore. Certain medicines may affect the results of this test. These include heparin and large doses of warfarin Coumadin. If you are taking these medicines, follow your healthcare provider's instructions. Your provider may want you to stop taking them before the test.
You don't need to prepare for this test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.
Board review style answer 2. Prekallikrein deficiency. Prekallikrein deficiency causes prolonged aPTT that corrects in a mixing study and is not associated with clinical bleeding. The other contact factors factor XII and high molecular weight kininogen give a similar picture.
Factor IX deficiency can also cause a prolonged aPTT that corrects in a mixing study but it is associated with a bleeding diathesis hemophilia B.
Some types of von Willebrand disease may be associated with prolonged aPTT e. Sign up for our Email Newsletters. Click here for information on linking to our website or using our content or images.
What is a PTT partial thromboplastin time test? What is it used for? A PTT test is used to: Check the function of specific coagulation factors. If any of these factors are missing or defective, it can mean you have a bleeding disorder.
Bleeding disorders are a group of rare conditions in which blood doesn't clot normally. The most well-known bleeding disorder is hemophilia. Find out if there is another reason for excessive bleeding or other clotting problems. These include certain autoimmune diseases that cause the immune system to attack coagulation factors.
Monitor people taking heparin , a type of medicine that prevents clotting. In some bleeding disorders, the blood clots too much, rather than too little. This can cause heart attacks , strokes , and other life-threatening conditions. But taking too much heparin can cause excessive and dangerous bleeding. Why do I need a PTT test? You may need a PTT test if you: Have unexplained heavy bleeding Bruise easily Have a blood clot in a vein or artery Have liver disease , which can sometimes cause problems with blood clotting Will be getting surgery.
Surgery can cause blood loss, so it's important to know if you have a clotting problem. Have had multiple miscarriages Are taking heparin.
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