Blood type and Rh Factor test (Blood Type, Rh Factor) – a laboratory test used to determine a person’s blood type according to the ABO system and their Rh factor. This information is primarily needed to select compatible donor blood. Blood type is also taken into account during organ transplantation, while the Rh factor has.
Blood Type
The AB0 blood group system is based on the presence or absence of antigens on the surface of red blood cells and antibodies in the blood plasma. The test is used to prevent a potential immune conflict when a blood transfusion or organ transplantation is required, as well as during pregnancy. The test is recommended before surgical procedures or other interventions that may require a blood transfusion, for candidates and donors of organs, tissues, or bone marrow, as well as for pregnant women during their first visit to a doctor and during a second pregnancy if the mother is Rh-negative and the father is Rh-positive or his Rh status is unknown. The result indicates which of the four ABO blood groups a person belongs to and whether the Rh factor is present or absent.
Red blood cells have antigens on their surface. The two main antigens embedded in the red blood cell molecule are antigens A and B. Blood groups are determined based on the presence or absence of these antigens. The blood of people whose red blood cells carry antigen A belongs to the second blood group, A (II), while the blood of those whose red blood cells carry antigen B belongs to the third blood group, B (III). If both A and B antigens are present on the red blood cells, this is the fourth blood group, AB (IV); if neither of these antigens is detected on the red blood cells, this is the first blood group, O (I). Normally, the body produces antibodies against those antigens (A or B) that are absent from the red blood cells.
People with the first blood group (especially O Rh−) are traditionally considered universal red blood cell donors. However, in modern medical practice, blood transfusions are performed after mandatory compatibility testing between the donor and recipient. Everyone who belongs to the fourth blood group is considered a universal recipient because the immune system recognizes all three antigens as its own. These rules apply only to red blood cells, not to plasma or platelets.
If a person needs to know their blood type and Rh factor, the laboratory performs this test either at a doctor’s referral or on the person’s own initiative. This laboratory diagnostic test is a method of determining blood type and Rh factor. Blood type is genetically determined and usually does not change under normal circumstances. However, for example, a bone marrow transplant from a donor with a different blood type may lead to a change in blood type over time.
Rh Factor
The Rh factor in blood is a protein found on the surface of red blood cells in some people. If it is present, a person is considered Rh-positive; if it is absent, they are considered Rh-negative.
The Rh factor is particularly important during pregnancy. Approximately 85% of people are Rh-positive and, accordingly, 15% are Rh-negative. If the mother is Rh-positive, her blood will be compatible with the baby’s blood in any case. If she is Rh-negative, there are several possibilities: if the baby’s father is also Rh-negative, the mother’s blood will be compatible with the fetus’s blood because the baby will also inherit Rh-negative status; if the father is Rh-positive and the mother is Rh-negative, there is a 50% probability that blood incompatibility between the mother and baby may occur – Rh incompatibility, which may lead to complications. When fetal blood enters the mother’s bloodstream, antibodies begin to be produced against its Rh factor because the proteins on the red blood cell molecules are recognized by the mother’s body as antigens. The antibodies cross the placenta into the fetal bloodstream, causing hemolysis. Hemolysis can lead to impaired fetal development and, in some cases, miscarriage; after birth, it can cause hemolytic disease of the newborn.
Determining blood type and Rh factor is a standard laboratory procedure performed using a venous or capillary blood sample. The results are used by doctors to ensure the safety of medical interventions, select appropriate donor blood, and clarify the individual characteristics of the body.
How to interpret the result
ABO blood group:
- Group O (I) – A and B antigens are absent from the red blood cells; antibodies against A and B antigens are present in the plasma.
- Group A (II) – antigen A is present on the red blood cells; antibodies against antigen B may be present in the plasma.
- Group B (III) – antigen B is present on the red blood cells; antibodies against antigen A may be present in the plasma.
- Group AB (IV) – both A and B antigens are present on the red blood cells; there are no antibodies against these antigens in the plasma.
Rh factor:
- Rh+ (positive) – Rh antigen D is present on the surface of the red blood cells.
- Rh− (negative) – Rh antigen D is absent.
The test result is recorded as a combination of blood type and Rh factor, for example: A (II) Rh+, O (I) Rh−, AB (IV) Rh+. The results are used by a doctor to assess blood compatibility and plan medical procedures safely.
