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What To Expect Before a Blood Transfusion

Before a blood transfusion, a technician tests your blood to find out your blood type (A, B, AB, or O) and whether you're Rh-positive or Rh-negative. He or she pricks your finger with a needle to get a few drops of blood or draws blood from one of your veins.

The blood type used for your transfusion must work with your blood type. If it doesn't, antibodies (proteins) in your blood attack the new blood and make you sick.

Some people have allergic reactions even when the donated blood does work with their own blood type. To prevent this, your doctor may prescribe a medicine to stop allergic reactions. (For more information, go to "What Are the Risks of a Blood Transfusion?")

If you have allergies or have had an allergic reaction during a past transfusion, your doctor will make every effort to make sure you're safe.

Most people don't need to change their diets or activities before or after a blood transfusion. Your doctor will let you know whether you need to make any lifestyle changes prior to the procedure.

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Blood Transfusion Clinical Trials

Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Blood Transfusion, visit

January 30, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.