Rh Blood Group System Flashcards
Rh blood group system general
2nd most important blood group system after ABO
5 principle antigens:
D, C, E, c, e
Rh gene organization
RhD & RhCE are 2 different genes on Chr. 1
transcribed in opposite directions -toward each other
RhD & RhCE arose recently from the duplication of one Rh gene
Rh protein function
traverses the membrane 12x; exact function is unknown- clearly a transport molecule
likely a CO2 transporter
necessary for membrane integrity!! People w/ Rhnull phenotypes have a hemolytic anemia
Rh system antigens
RHD: D antigen (37 epitopes) & G antigen
RHCE: C/c, E/e, G antigen, f ( compound of c&e epitopes), and Cw antigen
Rh antigen characteristics ( general)
protein antigen only
expressed ONLY on RBCs
present on RBCs at birth
autosomal codominant expression
D antigen statistics:
europe:
RhD pos 85%
RhD neg 15%
RhCE antigen Cw
mutation from glutamine at position 41 to arginine
can be involved in serious HDFN & mild transfusions reactions
found in 2% of whites; rare in black populations
G antigen
any person w/ D or C antigen has the G antigen
a patient w/ an anti-G antibody would look like they have two antibodies (antiD & antiC)
patients will receive RBC that are Rh D & C neg
Fisher-Race antigen terminology
D, C,c, E, e
Weiner Antigen terminology
RhD & RhCE are linked & inherited as a haplotype Rh pos: R0-cDe R1-CDe R2-cDE Rz-CDE Rh neg: r-cde r'-Cde r''-cdE ry-CdE
R0
cDe
R1
CDe
R2
cDE
Rz
CDE
r
cde
r’
Cde
r’’
cdE
ry
CdE
3 most common genotypes overall
R0 (cDe), R1 (CDe), r(cde)
most common genotype in white population
R1-CDe
most common genotype in the black population
R0- cDe
most common RhD negative genotype
r- cde
causes of Weak D expression
genetic- most often
position effect
partial D
Genetic Weak D
due to inherited weak expression of D antigen
occurs when one has one chromosome that does not code for D antigen & one intact allele that has mutated such that the protein is unstable
requires IAT to detect weak D
Weak D: position effect
D antigen is in ‘trans’ location to C antigen: cDe/CDe
detected at immediate spin w/ new antiD reagents
Weak D: partial D or D mosaic
one chromosome lacking D; one with part of D
possible for a person to be Rh pos & have an antiD antibody that are made against the missing epitopes
When to test for weak D
in RhD neg donors:
if positive for weak D the unit of donated blood is labeled as RhD positive
RhD neg infants: if child is weak D then mother should be treated again w/ anti-Rh
Lab detection of weak D
weak D uses IgG antiD
incubation, washing, addition of AHG
important to run an Rh control
Rh null phenotype
no detectable Rh antigens
absence of Rh antigens = mild hemolytic anemia
only receive blood from other Rh null people
Clinical significance of Rh system
IgG class - cross placenta & cause HDNB
antigenicity of Rh antigens
D>c>E>C>e
