Partial thromboplastin time
test for coagulation of the blood
The partial thromboplastin time (PTT), also known as the activated partial thromboplastin time (aPTT or APTT), is a blood test that characterizes coagulation of the blood. A historical name for this measure is the Kaolin-cephalin clotting time (KCCT), reflecting kaolin and cephalin as materials historically used in the test. Apart from detecting abnormalities in blood clotting, partial thromboplastin time is also used to monitor the treatment effect of heparin, a widely prescribed drug that reduces blood's tendency to clot.
The PTT measures the overall speed at which blood clots form by means of two consecutive series of biochemical reactions known as the intrinsic pathway and common pathway of coagulation. The PTT tests the function of all factors except factors VII factor and XIII. The PTT is often used in conjunction with another measure of how quickly blood clotting takes place called the prothrombin time (PT). The PT measures the speed of clotting by means of the extrinsic pathway and common pathway.
Methodology
Activated partial thromboplastin time (APTT) is typically analyzed by a medical technologist or laboratory technician, either manually or using an automated instrument at 37°C, which approximates normal human body temperature. Prothrombin time utilizes complete thromboplastin, a combination of tissue factor and phospholipids. In contrast, APTT employs partial thromboplastin, containing only phospholipids and no tissue factor—hence the term "partial thromboplastin time." An activator is used in the APTT test to initiate the intrinsic pathway of blood coagulation. Common activators include kaolin, silica, celite, and ellagic acid.
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