Lecture #149: Hematology: ABO Groups, RH Disease, Transfusion Medicine

What are the two main components of blood?

Plasma (~60 percent, containing antibodies) and formed elements (~40 percent, including RBCs and WBCs with antigens).

Why is blood type matching critical in transfusion?

Mismatched antigens trigger immune reactions leading to hemolysis, shock, renal failure, or DIC.

What are natural antibodies in transfusion medicine?

Primarily IgM antibodies formed without prior exposure, commonly against ABO antigens.

What are immune antibodies in transfusion medicine?

IgG antibodies formed after exposure to foreign antigens such as Rh, Kell, Duffy, or Kidd.

What type of hemolysis is caused by IgM antibodies?

Intravascular hemolysis due to complement activation.

What type of hemolysis is caused by IgG antibodies?

Extravascular hemolysis via opsonization and phagocytosis.

What is unique about ABO antibodies?

They are naturally occurring and can cause immediate severe hemolytic reactions.

What is the most clinically significant blood group system?

ABO system due to high immunogenicity and risk of acute reactions.

What determines ABO blood group antigens?

Carbohydrate structures added to the H antigen by glycosyltransferases.

What is the H antigen?

A precursor oligosaccharide structure on RBCs modified to form A or B antigens.

What defines blood type O?

Lack of active enzyme, leaving the H antigen unmodified.

What sugar is added in type A blood?

N-acetylgalactosamine.

What sugar is added in type B blood?

Galactose.

What is the Bombay phenotype?

A rare condition lacking H antigen, requiring transfusion only from similar individuals.

What type of antibodies are ABO antibodies?

IgM antibodies that cause agglutination and complement activation.

What is forward blood typing?

Detecting RBC antigens using known antibodies.

What is reverse blood typing?

Detecting serum antibodies using known RBC antigens.

What is hemagglutination?

Visible clumping caused by antigen-antibody interactions.

What is the purpose of Coombs (antiglobulin) testing?

To detect IgG antibodies that do not directly cause agglutination.

What does the direct antiglobulin test (DAT) detect?

Antibodies or complement bound to patient RBCs in vivo.

What does the indirect antiglobulin test (IAT) detect?

Free antibodies in patient serum against RBC antigens in vitro.

What is a type and screen (T and S)?

Determines blood type and screens for unexpected antibodies.

What is a crossmatch?

Testing donor RBCs against recipient serum to ensure compatibility.

What is the most immunogenic Rh antigen?

D antigen.

What does Rh positive or negative indicate?

Presence or absence of the D antigen.

Why is the Rh system clinically important?

Common cause of alloimmunization and hemolytic disease of the fetus and newborn.

What causes hemolytic disease of the fetus and newborn?

Maternal IgG antibodies against fetal RBC antigens, usually Rh(D).

How is Rh sensitization prevented?

Administration of Rh immune globulin to Rh-negative mothers.

What is the most common cause of acute hemolytic transfusion reactions?

ABO incompatibility.

What are features of acute hemolytic transfusion reactions?

Fever, hypotension, hemoglobinuria, renal failure, and DIC.

What is the first step in managing acute hemolytic transfusion reaction?

Stop the transfusion immediately.

What lab findings indicate hemolysis?

Increased LDH, bilirubin, decreased haptoglobin, and hemoglobinuria.

What characterizes delayed hemolytic transfusion reactions?

Drop in hemoglobin, positive DAT, and new antibody formation days after transfusion.

Which blood group systems commonly cause delayed reactions?

Rh, Kidd, Kell, and Duffy.

What causes febrile nonhemolytic transfusion reactions?

Cytokines from stored blood or antibodies to donor leukocytes.

What are symptoms of febrile nonhemolytic reactions?

Fever and chills without hemolysis.

What causes allergic transfusion reactions?

Antibodies against donor plasma proteins.

What are symptoms of allergic transfusion reactions?

Urticaria, bronchospasm, or anaphylaxis.

What is TACO?

Volume overload causing cardiogenic pulmonary edema after transfusion.

What are signs of TACO?

Hypertension, dyspnea, tachycardia, and pulmonary edema.

What is TRALI?

Non-cardiogenic pulmonary edema caused by donor anti-leukocyte antibodies.

What are features of TRALI?

Acute respiratory distress, hypotension, and hypoxemia.

What is transfusion-associated graft-versus-host disease?

Donor T cells attack recipient tissues causing multiorgan failure.

How is TA-GVHD prevented?

Gamma irradiation of blood products.

What causes septic transfusion reactions?

Bacterial contamination of blood products.

What are common organisms in septic transfusion reactions?

Gram-negative bacteria in RBCs and gram-positive bacteria in platelets.

What is leukoreduction?

Removal of leukocytes from blood products to reduce complications.

What does leukoreduction prevent?

FNHTRs, CMV transmission, and HLA alloimmunization.

What is the indication for packed RBC transfusion?

Hemoglobin less than 7 g/dL in most patients.

How much does one unit of RBC increase hemoglobin?

Approximately 1 g/dL.

What are indications for platelet transfusion?

Platelet count less than 10,000 or higher thresholds with bleeding or surgery.

What is fresh frozen plasma used for?

Replacement of clotting factors in bleeding or coagulopathy.

What is cryoprecipitate used for?

Fibrinogen deficiency, DIC, and von Willebrand disease.

What is albumin used for?

Maintaining oncotic pressure and volume replacement.

What is IVIG used for?

Treatment of immunodeficiencies and autoimmune diseases.

What are alternatives to transfusion?

Erythropoietin, autologous transfusion, and cell salvage techniques.