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Prothrombin Time

350
4.5
NABL, ISO
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Overview
Interpretations
FAQ's
Prothrombin Time

Overview of Prothrombin Time

What is Prothrombin Time?

The Prothrombin Time (PT) Test is performed to estimate the ability of the blood to clot in order to detect a bleeding disorder or clotting disorder and to monitor the effects of anticoagulant medication, warfarin.

Sample Type

The sample type collected for Prothrombin Time is: Blood

Preparation for Prothrombin Time

  • No special preparation required

Why Get Tested for Prothrombin Time?

The Prothrombin Time Test is performed:

·         To detect and diagnose bleeding disorder or clotting disorder

·         Before the surgical procedure

·         To monitor the efficacy of treatment with anticoagulating agent warfarin





Understand more about Prothrombin Time

In case of any bleeding, the body responds to stop the blood loss as quickly as possible by forming a blood clot. This process of blood clotting or coagulation is called hemostasis and involves a series of chemical reactions in the blood (coagulation cascade) which activates blood proteins called coagulation factors one after another in a series. The activated coagulation factors lead to the formation of fibrin mesh around the platelets and other blood cells at the site of bleeding and this complex hardens to form a “blood clot”.

Coagulation cascade proceeds by two pathways, the intrinsic pathway, and the extrinsic pathway. These pathways later merge together into a common pathway. Prothrombin (Coagulation Factor II) is converted to its active form thrombin in one of the reactions. The PT Test assesses the functioning of Blood Coagulation Factors I, II, V, VII, and X, which are parts of the extrinsic and common pathways by measuring the time taken for conversion of prothrombin to thrombin. The Activated Partial Thromboplastin Time (aPTT) Test measures the functioning of Blood coagulation Factors I, II, V, XII, VIII, IX, X, and XI, along with other factors Prekallikrein (PK), and High Molecular Weight Kininogen (HK) which form parts of the intrinsic and common coagulation pathways. The PT and aPTT tests are usually performed together and the results of both are evaluated simultaneously to determine the rate of blood clotting.

Warfarin is a drug prescribed in the treatment of conditions caused or worsened by excessive blood clotting like Deep Vein Thrombosis (blood clot formation in blood vessels), irregular heartbeats, etc. The PT test is also performed to evaluate the effectiveness of warfarin treatment. When performed to determine warfarin efficacy, the result of the PT Test is expressed in terms of a measurement scale called the International Normalized Ratio (INR). Since the PT Tests are performed using different reagents in different labs giving rise to widely varying results in other conventional units, the INR system was created to maintain uniformity in the results.


What Results of Prothrombin Time mean?

Interpretations

Normal Reference Ranges:

Prothrombin time (PT): 8.7-11.5 seconds

International normalized ratio (INR): 0.8-1.2

INR during Warfarin treatment: 2.0 to 3.0


Prothrombin time longer than the normal range indicates a bleeding disorder where blood takes a longer time to clot.

Prothrombin time shorter than the normal range indicates a clotting disorder where blood takes lesser time to clot.

The PT and aPTT tests are usually performed and evaluated simultaneously, and the results may be interpreted as follows:


PT  RESULT

 aPTT RESULT

CONDITIONS INDICATED

High

Normal

Liver diseases, Vitamin K deficiency, reduced activity of Factor VII, Disseminated Intravascular Coagulation (DIC), Warfarin treatment

Normal

High

Reduced activity of Factors VIII, IX, XI, or XII, von Willebrand disease, autoantibodies destroying one or more coagulation factors

High

High

Reduced activity of Factors I, II, V or X, liver diseases, DIC, an overdose of Warfarin

Normal

Normal

Normal hemostasis usually. However, normal results may also appear in a mild reduction in coagulation factor activity and mild cases of von Willebrand disease.


Patient Concerns about Prothrombin Time

Frequently Asked Questions about Prothrombin Time

Q. How is this test performed?
This test is performed on a blood sample. A syringe with a fine needle attached is used to withdraw blood sample from a blood vessel in your arm generally from the inner side of the elbow area. The doctor, nurse or the phlebotomist will tie an elastic band around your arm which will help the blood vessels to swell with blood and hence makes it easier to withdraw blood. You may be asked to tightly clench your fist. Once the veins are clearly visible, the area is cleaned with an antiseptic solution and then the needle is inserted into the blood vessel to collect the sample. You may feel a tiny pinprick during the procedure. Blood sample once collected is then sent to the laboratory.
Q. Is there any risk associated with this test?
There is no risk associated with the test. However, as this test involves a needle prick to withdraw the blood sample, rarely, a patient may experience increased bleeding, hematoma (blood collection under the skin) formation, bruising or infection at the site of needle prick.
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