Laboratory 1.3 - ABO Blood Groups

ABO blood group system

One of the most important and widely recognized blood type classification systems; categorizes blood into four main types based on the presence or absence of antigens on the surface of red blood cells

Agglutinogens

Specific types of antigens responsible for determining blood groups; the primary agglutinogens are the ABO and Rh antigens; important medically because they determine how the body reacts to blood from other people in transfusions, organ transplants, and pregnancy

Antibodies (blood typing)

Proteins in the plasma that react to specific antigens; bind to the antigen and alert the immune system to destroy or eliminate it; if a person receives blood with foreign antigens, their antibodies will attack them

Agglutinins

The antibodies that react to the ABO blood group antigens; the antibodies affecting blood type are anti-A (binds A antigens), anti-B (binds B antigens), and anti-Rh (binds Rh factor)

Agglutination

Clumping of cells that occurs when agglutinins encounter their specific agglutinogen

Self-antigens and antibody pairing

An individual's blood type is determined by the agglutinogen present on their RBCs, which are tolerated as "self" antigens; the blood will not have the matching agglutinin (since that would cause clumping) — e.g., a person with A antigens has anti-B antibodies, and vice versa

Transfusion reaction (cross-reaction)

Occurs when a patient's blood is not compatible with a donor's blood because the patient has antibodies that bind and destroy the donor blood

Hemolysis (Lab 1.3)

The lysing, or breaking, of blood cells; can occur due to a transfusion reaction and can be dangerous, causing anemia, renal failure, or disseminated intravascular coagulation (DIC)

Type A blood

Has A antigens on the RBC surface and anti-B antibodies in the plasma; can receive blood from A and O types; can donate blood to A and AB types

Type B blood

Has B antigens on the RBC surface and anti-A antibodies in the plasma; can receive blood from B and O types; can donate blood to B and AB types

Type AB blood

Has both A and B antigens on the RBC surface and no anti-A or anti-B antibodies in the plasma; known as the universal recipient, can receive blood from all ABO types; can donate blood only to AB types

Type O blood

Has no A or B antigens on the RBC surface and has both anti-A and anti-B antibodies in the plasma; known as the universal donor, can donate blood to all ABO types; can receive blood only from O type

Rh factor

Another crucial component of blood typing, determined by the presence or absence of the Rh antigen (D antigen); there are 8 Rh antigens, first identified in the Rhesus monkey (hence "Rh")

Rh-positive vs Rh-negative

If the Rh (D) antigen is present, blood type is Rh-positive (reported with a "+"); if absent, blood type is Rh-negative (reported with a "-")

Rh antibody production

Unlike the ABO system, Rh-negative individuals do not typically have anti-Rh antibodies present; these are only produced when an Rh-negative individual is exposed to the Rh antigen

Rh incompatibility scenario 1 (transfusion)

An Rh-negative individual receiving Rh-positive blood during a transfusion will develop antibodies to the foreign D antigen; hemolysis does not occur with that first transfusion (antibody production takes time), but a future Rh-positive transfusion will trigger a hemolytic transfusion reaction

Rh incompatibility scenario 2 (pregnancy)

An Rh-negative woman pregnant with an Rh-positive fetus (inherited from an Rh-positive father) will produce Rh antibodies due to mixing of maternal and fetal blood; a future pregnancy with another Rh-positive fetus can lead to hemolytic disease of the newborn as maternal Rh antibodies attack the fetal Rh-positive RBCs

RhoGAM

A treatment given to prevent hemolytic disease of the newborn; dampens the immune response and production of anti-Rh antibodies in Rh-negative mothers

Blood typing (procedure)

A laboratory procedure used to determine an individual's blood type; blood is mixed with anti-A, anti-B, and anti-Rh serum (antibodies) and observed for agglutination; if agglutination is present, the corresponding antigen is present on the RBCs

Blood typing tray/wells

A tray typically labeled with wells for A, B, and Rh; a drop of the blood sample is placed in each well, then a drop of the corresponding anti-serum (anti-A, anti-B, anti-D) is added and mixed to observe for agglutination

Interpreting ABO blood typing results

Agglutination in the 'A' well only indicates Type A; in the 'B' well only indicates Type B; in both 'A' and 'B' wells indicates Type AB; in neither well indicates Type O; agglutination in the 'Rh' well indicates Rh-positive, and no agglutination indicates Rh-negative