Haematology - Blood Transfusion

Question 1

ABO Blood Group

Answer 1

Naturally occurring innate antibodies against any antigen not present on own red blood cells, IgM, reactive at 37ºC, capable of full complement activation = haemolysis; A and B antigens formed by adding sugar residue onto common glycoprotein and fucose stem (H antigen) on red cell membrane, group O = only H stem; A gene = N-acetyl galactosamine (added by enzyme); B = enzyme adds galactose; A&B = codominant, O = recessive

Question 2

Rh system

Answer 2

• D gene = D antigen on red cell membrane (d gene is recessive and not on it), RhD negative (dd) can make anti-D antibodies (IgG) by transfusion or RhD positive blood or pregnancy with RhD positive foetus (must have RhD negative blood because otherwise delayed haemolytic transfusion reaction + anemia + high bilirubin (from haemolysis) + jaundice)
• HDN = haemolytic disease of newborn (if fetus is RhD positive, mother’s anti-D antibodies can cross placenta (only IgG can do this) and cause foetal hemolysis (severe = hydrops fetalis + death, otherwise after birth high bilirubin = brain damage))

Question 3

Other red cell antigens

Answer 3

Dozens, not routinely matched, ~8% of transfusion patients will form antibody to 1 or more antigens (once this happens must use antigen negative blood)

Question 4

Testing samples before transfusion

Answer 4

Patient blood sample-> red cells -> ABO group (with known anti-A and anti-B reagents), RhD group (with known anti-D reagent); select donor blood with same ABO and RhD groups, antibody screen -> patient plasma incubated with 2/3 different fully typed “screening” RBCs (with all clinically relevant blood group antigen), if negative any ABO/RhD compatible blood, if positive large panel of RBCs for cross-matching (patient serum mixed with chosen donor RBCs)

Question 5

Donor selection

Answer 5

• 17-70, no cardiovascular/neurological/other disease that makes donating blood dangerous for them, no predisposition for viral + bacterial + parasitic infections, no diseases/drugs, donor self-exclusion if at high risk of blood-borne infectious diseases (prevent issues with ion in window period)
• Tests: ABO and RhD, C, c, E, e and K, only ABO antibodies in donor plasma, cases of prion proteins found in lymphoreticular tissues (variant Creutzfeldt-Jacob disease, vCJD)

Question 6

Blood components

Answer 6

450 ml blood in plastic bag with anticoagulant, component therapy = more efficient and less wasteful, no risk of fluid overload if patient doesn’t need plasma, centrifuge bag (RBCs bottom, platelets middle, plasma top) then in satellite bags and cut free (closed system)