Other names: Activated Partial Thromboplastin Time; Partial Thromboplastin Time; PTT; Kaolin Cephalin Clotting Time (KCCT)

The PTT test measures the efficacy and functionality of the coagulation cascade; the coagulation cascade is used to produce blood clots when the body suffers an injury, which causes bleeding. The coagulation cascade helps to prevent further bleeding and also facilitates healing.

Why is the test used?

The PTT test is used to monitor heparin treatment and to investigate patients who have experienced problems with bleeding and clotting.

Usually, doctors order the test when a patient experiences abnormal clotting or persistent bleeding for no apparent reason.

How is the test performed?

The test is performed by taking a sample from a vein in the arm; in most cases, blood is taken from a vein on the inside of the arm. Once the sample has been collected, it will be bottled, sealed and labelled and then sent away to the laboratory.

What do the test results mean?

The results of the test show the efficacy and efficiency of the coagulation cascade; if the results show that the cascade is prolonged, this indicates that the blood is not clotting as quickly as it should; this could be due to several different factors, including:

  • Problems with the sample, including an insufficient sample, clotted blood in the sample and heparin contamination of the sample.
  • The presence of a non-specific inhibitor, such as LA (the lupus anticoagulant)
  • Inherited or non-inherited factor deficiencies
  • The presence of a specific inhibitor (this is rare): this involves antibodies attacking a particular factor
  • Anticoagulation therapy, either using heparin or warfarin
  • Leukaemia

PTT may be decreased following an accident or injury as the body produces an acute reaction.

Specific Blood Tests

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