What factors could affect my test results?
Various medications can affect the results. These include medicines used to help prevent blood clots, such as the following:
Other anticoagulants, such as direct thrombin inhibitors and factor Xa inhibitors
Other medications that can affect the results:
If the blood sample is not collected correctly, the test results may also be affected.
How do I prepare for this test?
You usually do not need to prepare for this test. Your healthcare provider will tell you if you will need to avoid eating or drinking in the hours leading up to the test. You may ask him to stop taking any medications that may affect the test results, especially those preventing blood clotting. Make sure your healthcare provider knows all the medicines, herbs, vitamins, and supplements you use. This includes over-the-counter medications and any illegal drugs you may be using.
Prothrombin time (PT) is a blood test that measures how long it takes for blood to clot. Prothrombin time can be used to check for bleeding problems. It is also used to check if medication to prevent blood clots is working.
A PT test can also be called an INR test. The INR (International Normalized Ratio) represents a way to standardize prothrombin time results, regardless of the analysis method. It allows your doctor to understand the results simultaneously, even when they come from different laboratories and different analysis methods. In some labs, only INR is reported, and PT is not reported.
Blood clotting factors are needed for blood to clot. Prothrombin, or factor II, is one of the clotting factors that the liver produces. Vitamin K is needed to make prothrombin and other clotting factors. Prothrombin time is an important test because it checks if five different blood clotting factors (factors I, II, V, VII, and X) are present. The prothrombin time becomes longer due to:
Blood-thinning medications, such as warfarin.
Low levels of blood clotting factors.
A change in the activity of any of the clotting factors.
The absence of any of the clotting factors.
Other substances, called inhibitors that affect clotting factors.
An increase in the use of clotting factors.
An abnormal prothrombin time is often caused by liver disease or injury or by treatment with blood thinners.
Why is it done?
When a person cuts and breaks a blood vessel, platelets clump together at the wound site and form a temporary plug to stop bleeding. To form a firm clot, a series of 12 plasma proteins, or clotting factors, work together to produce a substance called fibrin that seals the wound.
If the body does not produce a specific clotting factor or incorrectly, it may be due to a bleeding disorder known as hemophilia. Symptoms of bleeding disorders include the following:
bleeding that doesn't stop even after pressure is applied to the wound
heavy menstrual periods
blood in the urine
joint swelling or pain
If your doctor thinks of a suspected bleeding disorder, they may order a PT test to make the diagnosis. You can also order a PT test to make sure your blood clots generally before you have major surgery, even if there are no symptoms of bleeding disorders.
If you take the blood thinner warfarin, your doctor will order regular PT tests to ensure the dose you take does not make you susceptible to excessive bleeding.
The test can also be used to assess clotting in people with liver disease or vitamin K deficiency. This is because these conditions can trigger bleeding disorders.
Tell your doctor about all the medications and supplements you take, and they will tell you if you should stop taking them before the test. You may need to stop taking your blood thinners as they can affect your results. You will not need to fast before the test.
The PT ba will require a blood draw, which is an outpatient procedure usually performed in a diagnostic laboratory. The procedure only takes a few minutes and is relatively painless.
A nurse will use a small needle to draw blood from a vein (usually in your arm or hand), and a lab technician will add certain chemicals to check how long a clot has formed.
There are very few risks associated with having blood drawn for a PT test. However, because the test is usually performed in patients with bleeding disorders, these people are at a slightly higher risk of excessive bleeding and bruising (blood that collects under the skin).
You may feel a little dizzy or have discomfort or pain where the extraction was done. There is also a slight risk of infection at the puncture site.
The typical time it takes for your blood to clot is between 11 and 13.5 seconds if you are not taking blood thinners. If you are taking this type of medicine, clotting may take longer. If your blood clots are within regular times, chances are you either don’t have a bleeding disorder, or you are taking the proper dose of anticoagulant.
Conversely, suppose your blood does not clot in the expected timeframes. In that case, it is possible that the dose of warfarin you take is not correct or that you have liver disease, vitamin K deficiency or a bleeding disorder such as a deficiency of factor II. If you have a bleeding disorder, your doctor may recommend clotting factor replacement therapy or a transfusion of fresh frozen plasma or platelets.