Blood types


A blood type is a classification system used by healthcare providers to determine the compatibility of blood between individuals. There are four main blood types: A, B, AB, and O. Blood bank specialists identify your blood type by checking for the presence of antigens A and B on your red blood cells. They also check for a protein called the Rh factor, classifying your blood type as positive (+) if you have this protein, and negative (-) if you do not. This results in eight common blood types: A positive (A+), A negative (A-), B positive (B+), B negative (B-), AB positive (AB+), AB negative (AB-), O positive (O+), and O negative (O-).

Understanding blood types is crucial for safely transfusing donated blood and ensuring compatibility during organ transplants. Blood types need to be compatible to prevent adverse reactions during these medical procedures.


Blood bank specialists identify your blood type based on specific antigens present on your red blood cells. Antigens are markers that trigger an immune response in your body, distinguishing between substances that belong and those that do not.

When donated blood contains antigens that are recognized by your immune system as part of your own body, your blood type is compatible with that of the donor. This compatibility ensures that transfusions can be safely administered to patients, minimizing the risk of adverse reactions and optimizing medical treatment effectiveness.

When most people hear the term “blood types,” they typically think of A, B, AB, and O. Based on whether red blood cells have the A or B antigen, these letters categorize blood types. We refer to this as the ABO system.

  • Type A: The “A” antigen is present in red blood cells.
  • Type B: The “B” antigen is present in red blood cells.
  • Type AB: The “A and B” antigen is present in red blood cells.
  • Type O: Neither “A nor B” antigens are present in red blood cells.

The presence or lack of the D antigen, another marker of the Rh factor, determines whether a blood type is “positive” or “negative.” We refer this as the Rh system. The incidence of RhD positivity is higher than RhD negativity.

  • Positive (+): The RhD antigen is present in red blood cells.
  • Negative (-):The RhD antigen is not present in red blood cells.

The blood types that are safe for you to receive can be determined by healthcare providers using your blood type. It assists them in determining which recipients of your donated blood can safely receive it.

  • A (+): Blood types that you can receive include A(+), A(-), O(+), and O(-).
  • A (-): Blood types that you can receive include A(-) or O(-).
  • B (+): Blood types that you can receive include B(+), B(-), O(+), and O(-).
  • B (-): Blood types that you can receive include B(-) or O(-)
  • AB (+): You are compatible to receive any blood type.
  • AB (-): Blood types that you can receive includes AB(-) negative, A(-),B(-), or O(-)
  • O (+): Blood types that you can receive includes O(+) or O(-)
  • O (-): Blood type you can only receive is O(-).

The following blood types are either considered universal donor or universal recipient.

  • Universal donor: Blood type O negative (O-) is the universal donor, meaning it can be safely transfused to individuals with any other blood type because it lacks antigen markers that other blood types recognize as foreign. Providers often use type O negative blood in emergencies when rapid transfusion is needed. In contrast, for plasma donation, which involves the liquid part of blood, the universal donor is type AB.
  • Universal recipient: The universal recipient has blood type AB positive (AB+). Any other blood type can be safely used to give you blood. Your immune system is kept from attacking because your blood views all possible antigens as harmless.


Making sure that the blood donor and the beneficiary have compatible blood types is an essential component of blood donation. Your immune system may target given red blood cells if you get blood from a donor whose blood cells contain antigens that your body is unable to identify. The outcomes might endanger life.


Blood bank specialists can determine the antigens on your red blood cells through blood typing. This process involves mixing antibodies that target either antigen A or B with your blood sample. Antibodies are proteins your body produces to combat foreign substances called antigens. You can consult your healthcare provider to find out your blood type, as it may be on file with them. Alternatively, volunteering to donate blood can help you discover your blood type while benefiting others. At-home blood test kits are also available for purchase.

Knowing your blood type is crucial, especially if you ever need a blood transfusion. Your healthcare provider can ensure your safety by knowing which blood types are compatible with yours. Blood donation and receiving are safe processes, and you don’t need to be an expert on every microscopic cell marker. Blood collection facilities are equipped with mechanisms and security measures to ensure the safety of the blood donation procedure.

During pregnancy, a fetus can inherit its Rh factor—positive or negative—from either parent. If you are Rh negative and carrying a fetus with Rh-positive blood, complications can arise. At your initial appointment with an obstetrician, you will undergo a blood test to determine your blood type and an antibody screen. If your body reacts to Rh-positive red blood cells, anti-Rh antibodies may attack the fetus’s red blood cells. To prevent this, you will receive Rh immunoglobulin (RhIg), a medication that prevents antibodies from harming the fetus’s blood.