Chapter 6 Rh Blood Group System Flashcards
After ABO what is the 2nd most important blood group system?
Rh blood group system.
What does Rh positive mean?
A person has a D antigen on their RBCs.
There are more than 50 antigens identified in the system. D is the most clinically significant.
What is the most immunogenic antigen?
D antigen.
How much blood with D antigen can it take to stimulate an immune response?
Exposure to less than 0.1 mL can stimulate a response. This can occur through transfusion or while delivering a baby (or a traumatic pregnancy).
What are the 5 major Rh antigens (out of 50)?
D, C, E, c, e
What makes the Rh antigens different than most other antigens or is noteworthy?
Most RBC antigens include carbohydrates in their make-up but Rh antigens are only proteins.
Also it loops the membrane 12 times in short loops of amino acids on the exterior (no CHO). Therefore it is an integral part of the RBC and maintains its integrity.
What determines what antigens are present in the Rh system?
The antigen varies between two amino acids on specific spots in the long chain. This determines what antigens are present based on the genetic material inherited.
What antigens are antitheticals in the Rh system?
C, c, E, and e.
What type of genes control the expression of all Rh antigens?
Two closely linked genes (co-dominant alleles):
1. RHD gene - determines the expression of the D antigen.
2. RHCE gene: determines the expression of C, c, E, and e antigens.
What is the Fisher-Race terminology for the Rh antigens?
- Each gene expresses an antigen that is given the same letter as the italicized letter of the gene name (e.g., the C gene produces the C antigen).
- Order of genes is usually DCE (may be CDE)
- 8 possible set of genes inherited (from one parent):
Dce, DCe, DcE, DCE
dce, dCe, dcE, dCE
What is the wiener terminology based on?
8 alleles exist at the single Rh gene locus.
R0, R1, R2, Rz, r, r’, r”, ry
(subscripts, see slide 14)
Each gene encodes an agglutinogen (made of factors) that correlates with Rh antigens.
What is an agglutinogen?
A group of antigens or factors.
What (in general) is Rosenfield terminology for the Rh antigen system?
Indicates phenotype information more suited for computerized data entry.
Antigens are designated by number
Rh1:D
Rh2:C
Rh3:E
Rh4:c
Rh5:e
Example:
D+, C+, E–, c+, e+ is written as Rh:1,2,–3,4,5
What is the ISBT terminology?
International Society of Blood Transfusion
Attempts to standardize nomenclature
Six-digit numbers are assigned to each blood group specificity
The numbers 004 refer to the Rh system. The other numbers refer to the Rosenfield system (e.g., C antigen is RH2)
Example: ISBT number for the C antigen is 004002
How can genotypes be predicted without doing a molecular study?
Race can be used to predict the most probable genotype after the phenotype (i.e. antigen type) is determined.
What occurs after the immediate spin with a weak D antigen in phenotype testing?
A weak D may look negative with anti-D after immediate spin.
What do you do if you discover a weak D?
Follow through test into IAT phase for both D tube and Rh C tubes.
Antisera contains IgM and IgG.
What test can identify a weak D antigen?
RBCs that test positive only by the indirect antiglobulin test (IAT) are called Weak D antigens.
New monoclonal reagents have enhanced the detection of weak D antigens without the IAT.
What are the theories on the causes of a weak D expression?
There are three different theories of inheritance patterns:
1. Inherited Genetic Coding
2. Gene Position Effect
3. Partial D (also referred to as D mosaic)
What is the genetic reason for the weak D antigen (mutations that alter amino acids)?
Due to inheritance of a weaker form of the D antigen, often the cDe haplotype (R0)
Mutations that alter amino acids at the molecular level
More common in the black population (23%)
IAT is usually required to detect the weak antigen
Describe how position effect can cause a weak D antigen?
The D antigen may appear weak when the C antigen is inherited trans to D (2%)
Ce (r’) gene is paired with either Cde (R1) or cDe (R0)
How do newer monoclonal antisera blends help discover weak D when due to C trans to D?
Increased sensitivity of newer Anti-D are usually positive in the immediate spin phase
Patients are considered weak D positive and are able to receive D-positive blood
What does it mean to have a partial D antigen?
Individuals are D positive but are missing parts of the D antigen (partial D antigen)
When exposed to the “whole D antigen,” individuals may produce anti-D toward the missing part.
What can make you suspect a partial D antigen on a patient?
When a patient is D-positive but makes anti-D and it does not react with his or her own RBC.