blood group serology

Question 1

define blood group antigens

Answer 1

substances present on the surface of red cells

are normally glycolipids or glycoproteins

genetically determined

Question 2

glycoprotein determinants vs glycolipid determinants

Answer 2

protein determinants

• genes for the antigenic determinant itself
• e.g. Rh, Kell, duffy, Kidd systems

glycolipid determinants

• gene codes for productions of enzymes that add/remove carbohydrate or lipid structures
• e.g. ABO, lewis group system

Question 3

blood group antibodies

Answer 3

blood group antigen systems important as they stimulate antibody production

• antibodies recognise foreign antigens
• may be IgM, IgG, sometimes IgA
• may be naturally occurring or immune stimulated

Question 4

describe naturally occurring antibodies vs immune stimulated antibodies

Answer 4

naturally occurring

• no exposure to foreign red cells but exposure to bacteria containing for example, A-like antigen
• therefore anti-A produced
• related to glycolipid antigens
• IgM component to AB
• can activate complement

immune

• exposure to foreign red cells (for example Rh+)
• by transfusion
• or pregnancy (Rh+ fetes)
• anti-Rh produced
• related to glycoprotein antigen
• IgG component to AB

immune requires red cells, natural doesn’t

Question 5

incompatible transfusion

Answer 5

leads to complement activation
- red cells from donor carry antigen to AB in patient plasma

can cause:

• intravascular haemolysis
• renal failure
• disseminated intravascular coagulation (DIC)

Question 6

ABO

Answer 6

antigens widely distributed e.g. bloods cells, epithelial cells, body fluids

• all express H antigen
• vary depending on presence or absence of terminal sugar
• antibodies get formed in the first 3-6months when theres an absence of an antigen present

e.g.
phenotype = AA, AO
genotype = A
AB present = anti-B
donor = A, O

Question 7

Rh blood group system

Answer 7

• 2nd most important system
• Protein determinant
• Expression only on RBCs
• Antibodies produced following immune stimulation
• Highly immunogenic, particularly Rh (D)

Question 8

define agglutination

Answer 8

when antigen and antibody complexes come together they form a red cell clump

Question 9

Rh(D) and transfusion

Answer 9

• 90% of Rh(D) negative transfuse with Rh(D) positive cells will produce anti-D antibodies

anti-D is IgG and is unable to bind complement. Red cell destruction is extravascular

never transfuse Rh(D) positive cells to an Rh(D) negative female of child bearing age

Question 10

Rh(D) negative genotype

Answer 10

must have dd

cannot have any D genotype

Question 11

define zeta potential

Answer 11

Red cells are negatively charged, prevents them coming in contact with each other (no cross-linking and therefore no agglutination)

Question 12

IgM agglutination vs IgG

Answer 12

IgM > zeta potential
- cross-linking and agglutination forms

IgG < zeta potential

• no agglutination
• needs potentiator = anti-human globulin

Question 13

describe haemolytic disease of the newborn

Answer 13

• occurs when maternal AB crosses placenta leading to fatal red cell destruction
• involves IgG (as this crosses placenta)
• most frequently caused by anti-D
• reduced greatly by immunoprophylaxis

Question 14

mechanism of HDNB

Answer 14

Rh(D) -ve mother is exposed to Rh(D) +ve red foetal cells, most frequently following transplacental haemorrhage at delivery. This causes Rh(D) +ve cells to enter the maternal circulation and cause anti-D to form. Subsequent pregnancies, anti-D crosses the placenta and causes damage to foetal red cells

Question 15

consequences of HDNB

Answer 15

Foetal anaemia, develops cardiac failure –> congestive cardiac failure

More commonly survives pregnancy, baby jaundiced (bilirubin removed via maternal circulation) bilirubin crosses BBB and causes brain damage

Question 16

antenatal prophylaxis

Answer 16

• prevent mother from forming anti-D
• mother given injection of anti-D immunoglobulin –> clears D positive red cells –> stops primary response
• given following the birth of an Rh(D) positive baby to Rh(D) negative mother
• anti-D also given following events associated with transfer of red cells e.g. abortion, termination, amniocentesis

Question 17

kleihauer test

Answer 17

used to detect fatal cells in maternal blood, to detect women with larger foeti-maternal bleed (larger dose of anti-D immunoglobulin required)