International normalized ratio

International normalized ratio (INR) is a calculation made to standardize prothrombin time. INR is based on the ratio of the patient's prothrombin time and the normal mean prothrombin time. Prothrombin time is a test to learn how fast the blood clots in patients receiving oral anticoagulant medication. This test may be used in patients with prosthetic heart valves, venous thromboembolism, or antiphospholipid syndrome. A blood sample is collected for this test.

Laboratory tests may be done for many reasons. Tests are performed for routine health screenings or if a disease or toxicity is suspected. Lab tests may be used to determine if a medical condition is improving or worsening. Lab tests may also be used to measure the success or failure of a medication or treatment plan. Lab tests may be ordered for professional or legal reasons. You may need this test if you have:

• Antiphospholipid syndrome
• Atrial fibrillation
• Heart valve replacement - prosthesis
• Thrombophilia
• Venous thromboembolism

Before having blood collected, tell the person drawing your blood if you are allergic to latex. Tell the healthcare worker if you have a medical condition or are using a medication or supplement that causes excessive bleeding. Also tell the healthcare worker if you have felt nauseated, lightheaded, or have fainted while having blood drawn in the past.

A sample of blood from a vein or an artery may be collected for this test.

When a blood sample from a vein is needed, a vein in your arm is usually selected. A tourniquet (large rubber strap) may be secured above the vein. The skin over the vein will be cleaned, and a needle will be inserted. You will be asked to hold very still while your blood is collected. Blood will be collected into one or more tubes, and the tourniquet will be removed. When enough blood has been collected, the healthcare worker will take the needle out.

Before an arterial blood draw, the healthcare worker may check blood circulation to your arm or leg. Tell the healthcare worker if you use supplemental oxygen as this may affect the test results.

An artery in the wrist is the most common site to draw arterial blood. However, an artery at the inside bend of the arm or groin may be used. The area will be swabbed clean with antiseptic. Anesthetic may be used to numb the skin over the area where the blood will be drawn. A needle is used to puncture the skin. You will be asked to hold very still while your blood is collected. When enough blood is collected, the needle will be removed.

If you have an existing arterial catheter, a blood sample may be collected from that catheter.

Ask your healthcare worker if an INR testing device that can be used at home is an option for you.

The amount of discomfort you feel will depend on many factors, including your sensitivity to pain. Communicate how you are feeling with the person doing the test. Inform the person doing the test if you feel that you cannot continue with the test.

During a blood draw, you may feel mild discomfort at the location where the blood sample is being collected.

If you receive anesthetic to numb the skin before an arterial blood draw, you may feel discomfort at the location where the anesthetic needle is inserted into the skin. You may feel discomfort as the needle used to draw your blood is inserted into the skin, and you may have cramping at the site during the procedure. Inform the person doing the test if you feel faint or nauseated or if the discomfort is severe.

If blood is collected from an existing catheter inserted into an artery, you will feel little or no discomfort.

After a blood sample is collected from your vein, a bandage, cotton ball, or gauze may be placed on the area where the needle was inserted. You may be asked to apply pressure to the area. Avoid strenuous exercise immediately after your blood draw. Contact your healthcare worker if you feel pain or see redness, swelling, or discharge from the puncture site.

If blood was drawn from an artery in your arm or leg, cotton will be placed over the site and held firmly for at least five minutes to stop the bleeding. Bleeding may continue beyond five minutes if you are using medications or supplements that thin your blood or have a medical condition that causes excessive bleeding. When bleeding has stopped, a bandage will be placed firmly over the site and should be left on for 30 to 60 minutes. You should rest for at least 15 minutes after the test. Avoid heavy use of the arm or leg from which the blood was drawn for 24 hours after the blood is collected.

If blood was drawn from an existing catheter inserted into an artery, there are no special instructions for you after this test.

You have the right to help plan your care. To help with this plan, you must learn about your health condition and how it may be treated. You can then discuss treatment options with your caregivers. Work with them to decide what care may be used to treat you. You always have the right to refuse treatment.