Prothrombin Time (PT) Test and INR Test

PT INR Test

It is a simple blood test that is used to determine PT (prothrombin time) and INR (international normalised ratio). These tests are used to assess the clotting mechanism in our body along with one more test called as PTT (partial thromboplastin time).
Whenever there is some injury/bleeding in our body clotting mechanism is activated to form blood clots. This clotting prevents excessive blood loss .A number of clotting factors are needed for formation of bloodclots.Prothrombin is a type of protein made by the liver. It is one of the factor required in blood clotting .Hence low levels of these clotting factors cause excessive bleeding .High levels of these clotting factors may also cause excessive blood clots to form in our body which may block artery or vein.
Prothrombin time test helps to assess in how much time blood clots. INR is a type of calculation done from prothrombin (PT) blood test.

Why is PT INR test prescribed?

Your health care provider may ask you to undergo PT blood test in following circumstances:
1. When there is excessive bleeding, easy bruising, heavy nose bleeds, heavy menses etc to look for bleeding disorder
2. When there is leg swelling, chest pain, legpain, redness in legs, etc to look for clotting disorder
3. When you are taking blood thinning medications like warfarin on a regular basis to know the right dose
4. When you have to undergo some major surgery where there is risk of excessive bleeding

​What are the components of prothrombin time test?
The various tests done are-prothrombin time test, INR value .These tests may be done along with other test like PTT, platelet count, fibrinogen levels, coagulation factor tests, von Willebrand factor, lupus anticoagulant testing.

Procedure and prerequisites
The sample for PT/INR test is taken from the body by inserting a small needle into vein of your arm. A small amount of blood is then collected in a test tube or vial. You may feel a little pain due to needle prick. You may resume your daily activities immediately. If you are on warfarin then you should delay taking it after the test.

Reference range
1. For those taking warfarin INR should be adjusted to 2.0 to3.0
2. For normal people INR is less than 1.1
3. Normal range for blood clotting -11 to 13.5 seconds