How to find out your blood type most reliably is through a blood typing test. A healthcare provider can order this test at any time, and it is also routinely done when donating blood, before transfusions or transplants, and during prenatal care.
In some cases, blood typing is also done shortly after birth. Because of this, you may already be able to find your blood type in your medical records, such as your childhood health record or a hospital discharge summary, where the result is often listed.
The main blood types are A, B, AB, and O. Blood is also classified as Rh-positive when the Rh factor is present, or Rh-negative when it is absent.
Knowing your blood type is important because not all blood types are compatible. This helps reduce the risk of reactions during a blood transfusion and complications that can affect the baby’s health during pregnancy, for example.