What is a prothrombin Time analysis using INR (PT/INR)?
A prothrombin The time test (PT) determines how long it takes for a clot to form in a blood sample; the INR (International Normalized Ratio) is a picture of the calculation based on the results of the PT test.
Prothrombin is a protein produced by the liver. It is one of the various drugs popular as the moment of coagulation (clotting). When strained or otherwise damaged causing bleeding, coagulation moments work together to form a blood clot. Clots depend on the number of clotting moments in the blood and on the number of clotting moments in the blood and whether they work well together. If the blood is very slow, the patient may bleed profusely after an injury. If the blood clots very quickly, serious clots can occur in arteries and veins.
A PT/INR test can help diagnose underlying bleeding or clotting disorders. It also checks for proper functioning of clot-preventing medications.
Other names: prothrombin Time/International Normalized Compliance, PT Protome.
What is it used for?
The PT/INR test is used most often:
- To see how well warfarin is working. Warfarin is a blood drink used to treat and prevent unsafe blood clots (Coumadin is a commonly used brand name for warfarin).
- Recognize the Basis for Unusual Blood Clots
- Recognize the basis for abnormal bleeding
- Check coagulation function prior to surgery.
- Check for liver problems
PT/INR testing is often combined with a selective thromboplastin time test (PTT); the PTT analysis still checks for coagulation problems.
Why is a PT/INR test necessary?
If you are constantly using warfarin, you may need this analysis. This test helps ensure that you are taking the correct dose.
If you do not take warfarin, you may need this test if you have signs of bleeding or clotting disorders.
Symptoms of bleeding disorders include
- Unexplainably uncomfortable bleeding
- Simple bruising
- Unusually violent nose of blood
- Unusually slow menstrual periods in women
Symptoms of coagulopathy include
- Leg pain or sensitivity
- Swelling of the legs
- Redness or reddish streaks on the legs
- Shortness of breath
- Cough
- Chest pain
- Fast heartbeat
You may also need a PT/INR test if you are planning to have surgery. This will help ensure that your blood is clotting well. That way you will not lose too much blood during the procedure.
What happens during the PT/INR test?
This test can be performed with a blood sample from a vein or fingertip.
For a blood sample from a vein:
The physician takes blood from a vein in your arm with a small needle. After the needle is inserted, a small amount of blood is collected in a test tube or vial. You will feel some pressure as the needle goes in and out. This usually takes less than 5 minutes.
For blood samples via the fingertip:
The finger-tip option test can be done in the caregiver’s office or at home; if you take over Warfarine, your supplier can advise you to check your blood regularly with a PT/INR test kit at home. During this test, you or your supplier should
- Select a small needle on the end of your finger.
- Collect a drop of blood and do it on a test strip or another special instrument
- Place the instrument or test strip on the device to calculate the result. The instrument is small and light.
If you use a home use test kit, you should discuss your own results with your supplier. Your supplier will tell you how he or she would like to receive the results.
Do I need to prepare for the test?
If you use warfarin, you may need to defer your daily dose until after the test. Your health care provider will tell you if there are any other special instructions you should follow.
Are there any risks associated with the test?
There are considerable risks associated with blood testing. There may be slight soreness or bruising in the area where the needle is inserted, but most signs disappear quickly.
What do the results mean?
If you are tested because you are taking warfarin, the results will likely be in the form of an INR value; INR values are often used because they facilitate easy comparison of results from different labs and different test methods. When not taking warfarin, the results can take the form of an INR value or the number of seconds the blood clots (blood sample prothrombin time).
If warfarin is used:
- If the INR value is too low, it means that the risk occurs with dangerous blood clots.
- If the INR is too high, it means you are at risk for dangerous bleeding.
Your doctor will probably change your warfarin dosage to lower these risks.
If you do not take warfarin and your personal INR or prothrombin time results are not common and could mean one of the correct criteria.
- Bleeding disorder, a condition in which the body is unable to chop blood properly, causing excessive bleeding.
- Coagulopathy, a condition in which the body forms excessive clots in arteries or veins.
- Liver disease.
- Vitamin K deficiency. Vitamin K plays an important role in blood clotting.
What else do I need to know about the PT/INR test?
Certain liver tests may be ordered in combination with the PT/INR test. These include
- Aspartate aminotransferase (AST).
- Alanine aminotransferase (ALT).
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