Sunday, March 9, 2014

Prothrombin Time (PT)

Prothrombin Time (PT)

BackGround Information
Prothrombin time (PT) is a hematological test that determines how long it takes for a patient's blood to clot. It measures the extrinsic pathway of coagulation. This test is traditionally used to check for bleeding problems. Additionally, PT can also be used to check the efficacy of medicines that aids in preventing blood clots.

Prothrombin Time International normalized ratio (PTINR)

PTINR (international normalized ratio) is commonly measured to standardize the results of prothrombin time tests, as different automated hematological coagulation anaylzers and reagents (tissue factor) will yield different results. Hence, this allows physicians to interpret results correctly even though patients' results may come from different laboratories and different test methods. Therefore this PTINR system permits the treatment with blood-thinning medicine (anticoagulant therapy) to be effective. 
* Each manufacturer assigns an ISI value (International Sensitivity Index) for every tissue factor they manufacture. The ISI value indicates how a particular batch of tissue factor compares to an international reference tissue factor. The ISI is usually between 1.0 and 2.0. The INR is the ratio of a patient's prothrombin time to a normal (control) sample, raised to the power of the ISI value for the analytical system used.
Clinical Significance
Prothrombin (factor II), is one of the crucial clotting factors made by the liver. Vitamin K is essential to produce prothrombin and other clotting factors. PT test is essential to determine the presence and functionality of five vital blood clotting factors (factors I, II, V, VII, and X). Abnormally prolonged PT is often a result of underlying liver disease or injury or by treatment with blood thinners.
Prothrombin Time can be prolonged due to circumstances like:

  • Blood-thinning medicine, such as warfarin.
  • Low levels of blood clotting factors (factors I, II, V, VII, and X).
  • A change in the activity/functionality of any of the clotting factors.
  • The absence of any of the clotting factors.
  • Other substances or inhibitors, that affect the clotting factors.
  • An increased usage of the clotting factors.
Procedures for Manual PT Test Method
  • Ensure appropriate volume of blood in sodium citrated tube (Blue-top)
  • Centrifuge sodium citrated tube at a speed suitable to obtain platelet poor plasma (< 10 X 103/μL)
  • Pre-warm sufficient amount of Dade Innovin (~1200ul to run in duplicates with Low and High QC) at 37°C for 15 minutes
  • Pipette 0.1ml (100ul) of citrated plasma into a test tube preheated to 37°C
  • incubate for 3 minutes at 37°C
  • Pipette 0.2ml (200ul) of prewarmed Dade Innovin into plasma
  • Immediately upon addition of Dade Innovin, start the stopwatch and determine the clotting time.
  • The result is the elapsed time, in seconds, from the addition of the Dade Innovin into the plasma until the appearance of a solid gel clot
Reference Range

Normal Range: 9.6 - 11.6 seconds

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