Blood transfusions are generally considered safe, but there is some risk of complications. Mild complications and rarely severe ones can occur during the transfusion or several days or more after.
More common reactions include allergic reactions, which might cause hives and itching, and fever.
Blood banks screen donors and test donated blood to reduce the risk of transfusion-related infections, so infections, such as HIV or hepatitis B or C, are extremely rare.
Other serious reactions
Also rare, these include:
- Acute immune hemolytic reaction. Your immune system attacks the transfused red blood cells because the donor blood type is not a good match. The attacked cells release a substance into your blood that harms your kidneys.
- Delayed hemolytic reaction. Similar to an acute immune hemolytic reaction, this reaction occurs more slowly. It can take one to four weeks to notice a decrease in red blood cell levels.
- Graft-versus-host disease. In this condition, transfused white blood cells attack your bone marrow. Usually fatal, it's more likely to affect people with severely weakened immune systems, such as those being treated for leukemia or lymphoma.