Blood Groups and Transfusions

What are the two main physiological mechanisms by which the cardiovascular system minimizes blood loss?

By reducing the volume of affected blood vessels (vasoconstriction) and by increasing the production of red blood cells (erythropoiesis).

At what percentage of blood volume loss do pallor and weakness typically occur?

Loss of 15–30% of total blood volume.

What level of blood loss typically leads to severe shock?

Loss of more than 30% of total blood volume.

When are whole blood transfusions considered routine?

When blood loss is rapid and substantial.

What is packed red blood cells (PRBCs)?

A concentrated preparation of red blood cells obtained from whole blood by removing plasma, usually by centrifugation.

Why are packed red blood cells preferred over whole blood in many transfusions?

They restore oxygen-carrying capacity without unnecessary plasma volume.

Which anticoagulants are commonly added to collected blood and how do they work?

Citrate or oxalate; they prevent clotting by binding calcium ions (Ca²⁺).

What is the shelf life of collected blood stored at 4°C?

Approximately 35 days.

Why is donated blood separated into components?

Because blood is valuable and separating components allows each part to be used when and where needed.

What structures on red blood cell membranes determine blood type?

Highly specific glycoproteins located on the external surface of red blood cell plasma membranes.

What is the immunological role of red blood cell glycoproteins?

They act as antigens that can be recognized as foreign by the immune system.

What term is used for antigens that promote red blood cell clumping?

Agglutinogens.

What is agglutination in the context of blood transfusion?

The clumping of red blood cells due to antigen–antibody reactions.

Why can transfusion of incompatible blood be fatal?

Because it causes agglutination and destruction (hemolysis) of red blood cells.

How many genetically determined blood group systems exist in humans?

More than 20 blood group systems.

Which two blood group systems are most important for transfusion purposes?

The ABO system and the Rh system.

How many blood groups exist in the ABO system?

Four: A, B, AB, and O.

What is unique about the ABO blood group system compared to other systems?

The presence of preformed antibodies (agglutinins) in the plasma.

What are agglutinins?

Preformed antibodies in plasma that react against ABO antigens not present on a person’s own red blood cells.

When do ABO antibodies begin to appear in humans?

They begin appearing within 2 months after birth.

At what age do ABO antibody levels reach adult levels?

Between 8 and 10 years of age.

What antibodies are present in individuals with blood group O?

Both anti-A and anti-B antibodies.

What antibodies are present in individuals with blood group A?

Anti-B antibodies.

What antibodies are present in individuals with blood group B?

Anti-A antibodies.

Why do individuals with blood group AB not produce ABO antibodies?

Because they possess both A and B antigens, so neither is recognized as foreign.

What antigens are present on red blood cells of blood group A individuals?

A antigens.

What antigens are present on red blood cells of blood group B individuals?

B antigens.

What antigens are present on red blood cells of blood group AB individuals?

Both A and B antigens.

What antigens are present on red blood cells of blood group O individuals?

Neither A nor B antigens.

Why is blood group O considered the universal donor (ABO system)?

Because it lacks A and B antigens, so it does not trigger ABO antibody reactions.

Why is blood group AB considered the universal recipient (ABO system)?

Because it has no anti-A or anti-B antibodies.

What are Rh agglutinogens?

A group of antigens found on red blood cells, also called Rh factors.

How many Rh agglutinogens exist?

Approximately 50 different Rh agglutinogens.

Which Rh antigens are most common and clinically important?

C, D, and E antigens.

Which Rh antigen determines whether blood is Rh positive or Rh negative?

The D antigen.

Why is the Rh system named as such?

Because the D antigen was first discovered in rhesus monkeys.

What type of proteins are Rh antigens?

Transmembrane proteins with loops exposed on the red blood cell surface.

What percentage of the population is RhD positive?

Approximately 85%.

What percentage of the population is RhD negative?

Approximately 15%.

Do Rh-negative individuals naturally have anti-Rh antibodies?

No, anti-Rh antibodies are not spontaneously formed.

How do Rh-negative individuals become sensitized to Rh antigen?

By exposure to Rh-positive red blood cells through transfusion or pregnancy.

Why does hemolysis not occur after the first Rh-incompatible transfusion?

Because antibody production takes time after initial sensitization.

What happens during subsequent Rh-incompatible transfusions?

Anti-Rh antibodies cause hemolysis of donor red blood cells.

Can an Rh-positive person safely receive Rh-negative blood?

Yes, because Rh-negative blood lacks the D antigen.

What triggers a transfusion reaction in ABO incompatibility?

Recipient plasma agglutinins attacking donor red blood cells.

What is the first event in a transfusion reaction?

Agglutination of foreign red blood cells.

Why is agglutination dangerous during transfusion reactions?

It clogs small blood vessels and blocks blood flow.

What happens to agglutinated red blood cells after clumping?

They rupture (hemolysis) or are destroyed by phagocytes.

How does free hemoglobin cause kidney damage?

It enters kidney tubules, causing cell death and acute renal failure.

List systemic symptoms of a transfusion reaction.

Fever, chills, hypotension, tachycardia, nausea, vomiting, and general toxicity.

What is the main goal of treatment during a transfusion reaction?

Prevent kidney damage.

How is kidney damage prevented during transfusion reactions?

By administering fluids and diuretics to increase urine output and flush hemoglobin.

What is erythroblastosis fetalis?

Hemolytic disease of the newborn caused by Rh incompatibility.

What maternal and fetal Rh combination leads to erythroblastosis fetalis?

Rh-negative mother and Rh-positive fetus.

How does maternal sensitization occur during pregnancy?

Fetal Rh-positive red blood cells enter maternal circulation during placental bleeding.

Why is the first Rh-incompatible pregnancy usually unaffected?

The mother has not yet produced significant anti-Rh antibodies.

Why are subsequent Rh-incompatible pregnancies dangerous?

Maternal anti-Rh antibodies cross the placenta and destroy fetal red blood cells.

What are the consequences of erythroblastosis fetalis for the fetus?

Severe anemia, hypoxia, possible brain damage, or death.

How can severe erythroblastosis fetalis be treated before birth?

Intrauterine blood transfusions.

What is RhoGAM?

A preparation containing anti-Rh antibodies.

When is RhoGAM administered?

During pregnancy and after delivery in Rh-negative mothers with Rh-positive fetuses.

How does RhoGAM prevent erythroblastosis fetalis?

It blocks maternal immune sensitization to the D antigen.

What is the effect of plasma exchange in Rh-sensitized mothers?

It reduces circulating antibody levels by up to 75%.