Activated Partial Thromboplastin Time (APTT) Test
The activated partial thromboplastin time (APTT) and the partial thromboplastin time (PTT) tests are very similar in nature and are used to test the amount of time taken by blood to clot in a patient being treated with blood-thinning medicines, especially heparin. The normal lab values of APTT and PTT are different as there are differences in the norms of people undergoing coagulation therapy. Many blood proteins and factors are necessary for clotting to occur in order to stop bleeding. The APTT test is performed after a patient has regularly taken blood-thinning medicines for a specific period of time, so that the exact dose and dosage of the medicine that can be safely taken for life can be determined for that particular patient.
The APTT test is also performed to detect the possible cause of unusual bleeding or bruising, to screen the deficiency of some blood clotting factor leading to bleeding disorders like hemophilia, to ascertain the blood clotting time before surgery, and to determine the most effective dose of medications like heparin. In such cases, the test is repeated every few hours to check the response. Once the correct dosage is determined, the frquency of the test is decreased.
An elastic belt is wrapped around your upper arm to obstruct the blood flow. This causes the veins below the belt to become more prominent, thereby making it easy for the phlebotomist to insert the needle into the vein to draw blood. The site to be punctured is cleaned with surgical spirit and the needle is then gently introduced into the vein and the required amount of blood is drawn into the syringe. The needle is then withdrawn, a wad of cotton soaked in surgical spirit is pressed over the punctured site, and the belt is removed from your arm. Finally, after the bleeding stops owing to pressure, the wad of cotton is thrown away and a piece of micropore tape is applied over the site.
The normal values of APTT differ from lab to lab. Generally, the time taken for blood coagulation ranges between 25 and 39 seconds. There could be a deficiency of one or more clotting factors if the time taken for blood clotting is longer than normal. It may be indicative of a bleeding disorder like hemophilia. Sometimes, diseases related to the liver or kidney, or treatment with drugs used to prevent blood clot formation (like heparin) may be responsible for increased APTT.
Rarely, complications may arise as a result of venepuncture done to collect the patient's blood sample. A bruise may develop over the punctured site. Sometimes, inflammation of the vein, medically known as phlebitis, may occur. In such cases, application of warm compresses several times daily can help to reduce the discomfort. Certain herbs, high doses of vitamin C, and medicines like antihistamines can alter the results of the APTT test by temporarily prolonging the clotting time.
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