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Partial Thromboplastin Time (PTT) Test

Last updated Nov. 17, 2018

The Partial Thromboplastin Time (PTT) Blood Test assesses the integrity of the intrinsic and common pathways. It reports the time taken for a clot to form (or the clotting time) in a serum sample, after the necessary factors are added.


What are the other Names for this Test? (Equivalent Terms)

  • Activated Partial Plastin Time Blood Test
  • aPTT Blood Test
  • PTT Test

What is Partial Thromboplastin Time (PTT) Test? (Background Information)

  • Partial thromboplastin is a synthetic derivative of a blood clotting protein called thromboplastin, also known as tissue factor or factor III
  • Clotting occurs, when an enzyme called thrombin, converts a soluble protein (fibrinogen) into its insoluble form (fibrin). These proteins then aggregate and form a blood clot
  • Thrombin is activated by the convergence of two pathways, called the intrinsic and extrinsic pathways. These are initiated by different parts of the body, after an external insult to bodily tissues:
    • Intrinsic begins in blood, with the activation of already circulating proteins
    • Extrinsic begins in the blood vessel, with the secretion of protein factors by damaged cells, lining the blood vessel
  • The extrinsic pathway is the first to activate; the damaged vessels expose underlying collagen and secrete protein factors. The intrinsic pathway then reinforces the extrinsic and provides longer-lasting clotting effects
  • Each pathway utilizes specific factors that are made in the liver. In addition, calcium and vitamin K are essential to both the pathways
  • In the body, complete thromboplastin resides in the connective tissue. When an injury occurs, thromboplastin is exposed and initiates both the intrinsic and extrinsic clotting pathways
  • Partial thromboplastin is a stripped-down version of the natural enzyme that only activates the intrinsic and common pathways
  • The Partial Thromboplastin Time (PTT) Blood Test assesses the integrity of the intrinsic and common pathways. It reports the time taken for a clot to form (or the clotting time) in a serum sample, after the necessary factors are added
  • An “activator” is sometimes added to speed up the test and make the results more reproducible. But, this also narrows the range of time values and decreases the test’s sensitivity

What are the Clinical Indications for performing the Partial Thromboplastin Time (PTT) Test?

The following are clinical indicators for performing a Partial Thromboplastin Time Test:

  • Chronic anemia
  • Excessive bleeding
  • Monitor anticoagulant therapy
  • Assess clotting ability before surgery
  • Differentiate between problems in the intrinsic and extrinsic clotting pathways

How is the Specimen Collected for Partial Thromboplastin Time (PTT) Test?

Sample required: Blood

Process: Insertion of a needle into an arm vein.

Preparation required: None

What is the Significance of the Partial Thromboplastin Time (PTT) Test Result?

Prolonged partial thromboplastin time may indicate:

  • Liver disorder
  • Bone marrow disorder
  • Vitamin K deficiency
  • The individual is on anticoagulant therapy
  • Afibrinogenemia
  • Collagen disorder
  • Disseminated intravascular coagulation (DIC)
  • Cancer
  • Polycythemia
  • Chronic pancreatitis
  • Toxic shock syndrome
  • Genetic disorders involving the clotting factors of the intrinsic and common pathways
  • Lupus anticoagulants
  • von Willebrand’s disease

Accelerated PTT may indicate:

  • Predisposition to clot formation within the blood vessels (thrombosis)
  • Blockage of blood flow (embolism)
  • Tissue damage, due to lack of blood flow (infarction)
  • Multiple myeloma

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • The prothrombin time (PT) test assesses the extrinsic and common pathways. Thus, PTT and PT Tests are often performed together, in order to more completely evaluate the integrity of the coagulation cascade
  • Certain factors may interfere with the test and these include: Heparin and metformin (if not being measured), salicylates, steroids, alcohol, antibiotics, birth control pills, caffeine, and recreational drugs

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

References and Information Sources used for the Article:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: March 12, 2014
Last updated: Nov. 17, 2018