Prothrombin Time (PT/INR)
Prothrombin Time (PT/INR)
Prothrombin is one of several proteins produced by the liver that helps in blood clotting. When you have a cut or an injury, your clotting factors collaborate to stop the bleeding.
A prothrombin time (PT) test determines how long it takes for a clot to form in a blood sample. The test's results are frequently expressed in seconds or as the International Normalized Ratio (INR). If the time it takes for the clot to form is too long, it may be an indication of excessive bleeding. On the other hand, if the time it takes for the clot to form is too short it may be an indication of the risk of developing blood clots in your arteries and veins.
Other names of prothrombin time are PT protime, Prothrombin time/International Normalized Ratio
What is PT/INR test used for?
A prothrombin time is most often used to:
Monitor Warfarin treatment (Warfarin is a blood-thinning agent prescribed to treat and prevent blood clots)
Understand the reason behind abnormal blood clots
Understand the reason behind abnormal bleeding
Monitor clotting function before a surgery
Find out liver abnormalities
Test along with Partial thromboplastin time (PTT).
Who should get tested?
A prothrombin time is indicated in individuals who
Take warfarin medicine on a regular basis
Have symptoms of bleeding or clotting
Bruise easily
Have severe nose bleeds
Have unusually heavy menstrual bleeds (in women)
Have liver problems
Test preparation:
No special preparations are required to undergo prothrombin time test. Your healthcare provider will insert a small needle into a vein in your arm and draws a few mL of blood into a sterile test tube.
Please tell your healthcare provider if you are taking any prescription or non-prescription medicines such as Ayurveda or herbal drugs
Test results of prothrombin time are usually measured in seconds. However, if you take warfarin your test results will be given as INR.Â
Normal results vary based on the warfarin use in individuals.
People who take warfarin: INR 2.0 – 3.0
People who don’t take warfarin: INR 0.8 – 1.1
In seconds: 11 – 13.5 seconds
Â
Deviations from the normal ranges:
Prothrombin time in seconds (for people who don’t take warfarin):
·      Higher than normal ranges may be an indication of blood taking longer than usual to clot
·      Lower than normal ranges may be an indication of blood clotting too quickly than expected
·      This could be either due to vitamin K deficiency (which plays an important role in blood clotting), liver disease, or coagulation factor deficiency.
Prothrombin time in INR (for people who take warfarin):
·      Low levels of INR values (<2.0) may mean that your blood is clotting too quickly than normal and you may be at risk for dangerous blood clots.
High levels of INR values (>3.0) may mean that your blood is clotting too slowly than normal and you are at high risk of developing serious bleeding.
FAQs
What is the turnaround time (TAT) for prothrombin time?
The test results are usually available within 1 – 2 working days after the sample collection. However, it could also take a little longer at times
Are there any risks associated with Prothrombin time?
No, there are no potential risks associated with prothrombin time. However, all blood tests involve negligible risks such as feeling a slight sting or bruise at the site of needle insertion. It usually resolves within a few minutes to hours. Rarely, the site can become infected
What medications may interfere with my prothrombin time test results?
A few medications such as antibiotics, barbiturates, oral contraceptives, hormone replacement therapy, aspirin, heparin, antihistamines, etc. may affect your test results. It is always advised to tell your healthcare provider about all the medications that you use before undergoing the test.
Apart from medications, certain supplements such as vitamins K and C, food, and alcohol may also interfere with the test results of prothrombin time
Why are the PT/INR test results high in people taking warfarin?
The test results of prothrombin time are often high in people taking warfarin due to:
·      Improper dose of warfarin
·      Taking over-the-counter medicines such as medicines for cold or vitamin supplements that could interact with warfarin
·      Alcohol consumption
Taking foods such as kale, spinach, cranberry juice, etc. that could interact with warfarin
How often do I need to take PT/INR tests if I take warfarin?
If you are taking warfarin, you will need regular PT/INR monitoring to see the response of warfarin.
·      Initially, it is tested on a daily basis until the desired range is acquired.
Once stable, you can get tested every two weeks and the testing time can be stretched to 4 to 8 weeks later
Related tests
Tests At Lupin Diagnostics