Immunohematology Flashcards
What does the H-gene code for?
L-fucose which binds to RBC oligosaccharide side chains
(person may be HH or Hh and still produce the enzyme (L-fucosyltransferase), but hh produces no enzyme))
A gene adds ____ to L-fucose; B gene adds _____ to L-fucose.
- N-acetylgalactosamine
- D-galactose
(O gene→ oligosaccharide chain + L-fucose)
Bombay blood type
homozygous hh → no pre-cursor antigen H (L-fucose) → no A or B expression
(L-fucose allows expression of A and/or B Ags on RBC)
Bombay Blood group appears to be ____ type blood.
O type
(serum from Bombay individual will agglutinate type O cells; they have anti-A, anti-B, anti-H Abs)
Landsteiner’s Law
When sugar antigen is present on the RBC, the corresponding Ab will be absent from the serum
Blood antigens are not consistent; give 3 examples of blood antigens that change over time
- I Antigen: ⇡ w/maturity
- Lewis group: ⇣ in pregnancy
- A/B Ags: altered w/disease
Non-immune antibody
IgM: anti-A & anti-B (made w/o previous exposure)
IgM & IgG can both fix complement, but IgG must _____
have another IgG to do it; IgM only needs one
Forward typing tests for _____; Reverse typing tests for _____.
- blood group Ag (on RBCs)
- serum Ab
(must match them, forward typing = blood group Ag testing)
What does a positive Direct Coomb’s Test indicated?
patient serum has IgG Abs bound to the RBCs
(ex: erythroblastosis fetalis)
What does a positive Indirect Coomb’s Test indicate?
serum Ab
(ex: Rh- mother gets tested to see if she has anti-RhD abs that will attack an Rh+ fetus)
What is the difference between warm & cold agglutinins?
- warm: IgG, reacts at body temp (35-37 C) → cause immune response
- cold: IgM, react at temps below body temp (Ii system)
(both are Abs against blood group Ags. Warm = clinically relevant)
Warm agglutinins can cause ______.
hemolytic transfusion reactions
(prior exposure → ab production (warm agglutinin))
Agglutination is a _____ reaction
serologic
(RBCs Ag forms parrticles when coated in Abs)
In In vitro agglutination reactions, IgG are _______(always/not at all) visible w/RBC ags; IgM are _______ (always/not at all) visible
- not at all
- always
(IgGs are small and RBC are usually far apart)
Hemolysis
Ab-coating → complement activation = lysis
(pink-red supernatant from freed Hgb. This cannot be used for lab testing!)
Hemolytic disease of the newborn is caused by _______.
RhD- mother has RhD+ baby → at birth, mom is sensitizes to RhD+ → antibodies will attack future RhD+ baby → hemolytic disease of the 2nd baby
hemolytic reaction is a _______ reaction to the _____.
- type II hypersensitivity
- Ag on RBC/additional sugar on cell-surface glycolipids
What is a cross-match test?
patients serum is tested before transfusion against ABO/RhD matched donors; only RBC NOT BOUND by Abs may be used otherwise → hemolytic reaction
(donor serum not tested w/patient RBC bc there isn’t enough Ab to show agglutination rxn)
D mosaic
patient has inherited some Rh+ antigen
Weak expression of D
partial Rh+ that does not react w/Anti-D antibodies (anti-Rh)
Weak D expression causes (3)
- Genetic: low density of D Ag
- Position: trans position of C gene → D gene
- Mosaic: partial D expression (absence of portion of D Ag)
Lack of Duffy antigens is associated with ______.
resistance to malaria
Symptoms of Rhnull
- hemolysis
- stomatocystosis
- spherocytosis
- osmotic fragility
(they may only receive blood from other Rhnull)
