What blood tests do I need?
A small amount of your blood will be tested to find out how fast your blood clots. This is done with a fingerstick or a blood draw from your arm with a needle poke. This blood test is called an International Normalized Ratio (INR). Your care team may also get your prothrombin time, which is also called protime (PT).
Why do I need blood tests?
- Keeping your blood from clotting is a delicate process that is watched closely by your care team. An INR range will be set for you.
- If your INR stays within your range, your chance of bleeding or getting a clot is small.
- If your INR is above your range, you may be at a higher risk for bleeding.
- If your INR is below your range, you may be at a higher risk for making a blood clot.
This is why your blood needs to be tested often. Blood tests are done so your care team will know if the dose is right for you. In other words, your warfarin dose is keeping your INR in your goal range. This keeps you safe from bleeding and making clots.
Some patients can get a meter to test their INR at home. It is called a home fingerstick device. Ask your care team if you can get this.
How often do I need an INR?
When you start warfarin, you may need to have blood tests every 1 to 3 days or weekly. When your INR and warfarin dose are stable, blood tests are often done every 2 to 4 weeks, sometimes longer. If your dose changes, you may need to have your INR tested more often. It is very important to have your blood drawn when you are told. Call your care team if you cannot make a visit so you can reschedule.
What can change my INR?
There are some things that may change your INR. It is important to tell your care team about any of the changes below. You may need an INR test or to have your dose of warfarin changed.
These can change your INR:
- Illness, such as diarrhea or fever
- Eating more or less of foods that have vitamin K
- Changes in medicines (prescriptions, over-the-counter medicines, herbals, or natural supplements)
- How much alcohol you drink
- Missing doses
- Changes in your weight
- Changes in your activity level