Prothrombin time is a type of an investigatory test which helps us to know how much time blood takes to clot. This test is usually done to check for bleeding problems. It is also a test to check the efficacy of a medicine in case of bleeding problems.
A prothrombin time test is sometimes referred to as the INR test which stands for the international normalized ratio.
Clotting factors are needed for the blood to clot by a process of coagulation. There are about twelve clotting factors present in the body. Prothrombin which is also the second factor is synthesized by the liver. Vitamin k is an important factor as it helps in the synthesis of prothrombin. Prothrombin time test helps to determine the presence of the five clotting factors in the blood. Hence this test is important especially while detecting any kind of bleeding disorder.
An abnormal prothrombin time is caused by any kind of liver disease or injury or in cases where treatment with heparin which is an anticoagulant is advocated.
Prothrombin time test is done in the following cases:
-To check for any kind of abnormal bleeding.
-To detect any kind of unexplained bruising.
-To check the efficacy of blood thinners like warfarin. When this drug is being tested, a prothrombin time test is done. This is basically useful in knowing the correct amount of dosage of the drug needed.
-To check for vitamin k level in the body. Vitamin k is essential for the synthesis of various clotting factors.
-To determine low levels of clotting factors in the body as in cases of hemophilia (bleeding disorder)
-Also done as a part of the liver function test.
Procedure of the prothrombin time test:
A band is tied around the upper arm which sort of stops the blood flow. By doing so the veins under the band become prominent and blood can easily be drawn into a needle. A tube is then connected to the needle into which the blood is drawn. The band is removed after the blood is drawn and pressure is applied on the area where the needle was inserted after which a bandage is put on that particular area.
In normal conditions the values are as follows:
Prothrombin time (PT): 11-13 seconds
International standardized ratio (INR): 0.8-1.1
If any abnormal prothrombin time is detected it means the following:
-If the prothrombin time is more than normal, it can mean the lack of one of the clotting factors. The various clotting factors are the factor I, factor II, factor V, factor VII and factor X
-it could also show the presence of any kind of liver disease such as cirrhosis of the liver, any kind of injury or the absence of vitamin k.
-a serious life threatening condition known as the disseminated intravascular coagulation exist when there is a longer than normal prothrombin time. In this condition all the clotting factors of the body are used up very quickly. Due to which the blood is unable to clot and the normal clotting process is affected. Hence the bleeding cannot stop.
-an increase in the prothrombin time is also seen when blood thinners like heparin and warfarin are used.
This test can be affected when a person takes any kind of medicine which may alter the test results or in cases of severe diarrhea and vomiting. Drinking lot of alcohol or taking laxatives may also alter the test results.
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