page_title: Partial thromboplastin time
section_title: Methodology
hierarchical_section_title: Partial thromboplastin time / Methodology
caption_attribution_description: English: Blue Top Vacutainer tube used for PT and PTT blood tests
context_page_description: The partial thromboplastin time or activated partial thromboplastin time is a blood test that characterizes coagulation of the blood. A historical name for this measure is the kaolin-cephalin clotting time, 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.
  Partial thromboplastin time measures the overall speed at which blood clots by means of two consecutive series of biochemical reactions known as the intrinsic pathway and common pathway of coagulation. PTT measures the following coagulation factors: I, II, V, VIII, X, XI, and XII.
  The partial thromboplastin time is often used in conjunction with another measure of how quickly blood clotting takes place called the prothrombin time. The prothrombin time measures the speed of clotting by means of the extrinsic pathway.
context_section_description: Partial thromboplastin time is typically analyzed by a medical technologist or a laboratory technician on an automated instrument at 37 °C (as a nominal approximation of normal human body temperature). The test is termed "partial" due to the absence of tissue factor from the reaction mixture.
  Blood is drawn into a test tube containing oxalate or citrate, molecules which act as an anticoagulant by binding the calcium in a sample. The blood is mixed, then centrifuged to separate blood cells from plasma (as partial thromboplastin time is most commonly measured using blood plasma).
  A sample of the plasma is extracted from the test tube and placed into a measuring test tube.
  Next, an excess of calcium (in a phospholipid suspension) is mixed into the plasma sample (to reverse the anticoagulant effect of the oxalate enabling the blood to clot again).
  Finally, in order to activate the intrinsic pathway of coagulation, an activator (such as silica, celite, kaolin, ellagic acid) is added, and the time the sample takes to clot is measured optically. Some laboratories use a mechanical measurement, which eliminates interferences from lipemic and icteric samples.
caption: Blue Top Vacutainer tube used for PT and PTT blood tests
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