Blood Grouping & Rhesus (Rh) Factor is a laboratory test that determines your blood type (A, B, AB, or O) and your Rh status (Rh-positive or Rh-negative). Together, these results are often written as A+, A−, B+, B−, AB+, AB−, O+, or O−.

This test measures specific markers (called antigens) on the surface of your red blood cells:

• ABO blood group: looks for A and/or B antigens. People with type O have neither A nor B antigens.
• Rhesus (Rh) factor: most commonly checks for the D antigen. If D is present, you are Rh-positive; if absent, you are Rh-negative.

What the results mean in plain language: your blood group and rhesus factor help determine which blood types are safe for you to receive in a transfusion, and they are especially important during pregnancy. If an Rh-negative person is exposed to Rh-positive blood (through transfusion or pregnancy), their immune system may produce antibodies that can cause complications in future transfusions or pregnancies.

Doctors order blood grouping and rhesus factor testing whenever knowing your blood type is important for safety and medical planning. It is commonly done:

• Before a blood transfusion or when a transfusion may be needed (e.g., surgery, trauma, severe anemia) to ensure compatible blood and reduce the risk of a transfusion reaction.
• During pregnancy (often at the first prenatal visit) to identify Rh-negative mothers who may need prevention for Rh incompatibility (such as anti-D immunoglobulin) and to support safe pregnancy care.
• For organ or tissue donation/transplant planning, since ABO compatibility is an important part of matching.
• In emergencies where rapid blood typing is required (accidents, major bleeding, emergency surgery).
• For newborn evaluation when there is concern for blood group incompatibility between mother and baby, or if the baby shows signs of jaundice/anemia.

You may also choose to have this test as part of general health records so your blood group and rhesus status are known ahead of time, which can be helpful in urgent situations.

• Hemolytic disease of the newborn (erythroblastosis fetalis) due to Rh incompatibility
• ABO incompatibility in pregnancy/newborn (a cause of neonatal jaundice)
• Hemolytic transfusion reaction (from incompatible blood transfusion)
• Alloimmunization (development of antibodies after exposure to different blood group antigens)
• Severe anemia requiring transfusion support (e.g., iron-deficiency anemia, hemolytic anemia)
• Bleeding/hemorrhage situations requiring urgent transfusion (e.g., trauma, gastrointestinal bleeding)

• Improving transfusion safety by confirming the correct blood group and rhesus status
• Pregnancy planning and prenatal care, including prevention of Rh sensitization
• Emergency preparedness (having your blood type on file for urgent care)
• Pre-surgical assessment and readiness for potential blood loss
• Supporting safe blood or organ donation and compatibility planning