Chapter 7 The Rh Blood Group System

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Questions and Answers

In which of the following scenarios can anti-D immunoglobulin administration prevent Rh D immunization?

  • A D-positive mother immediately after delivering a D-negative baby.
  • A D-positive mother carrying a D-negative fetus.
  • A D-negative mother immediately after delivering a D-positive baby. (correct)
  • A D-negative mother who has already developed anti-D antibodies.

A D-negative pregnant woman is identified as having a weak D antigen expression. According to the content, what is the recommended course of action regarding Anti-D prophylaxis?

  • Withhold Anti-D immunoglobulin as the weak D antigen offers sufficient protection.
  • Administer Anti-D immunoglobulin prophylactically, as if she were D-negative. (correct)
  • Administer Anti-D immunoglobulin only after confirmation of fetal Rh status.
  • Monitor Anti-D antibody levels monthly rather than administering Anti-D immunoglobulin.

A patient with Dce/dCe genotype exhibits weak expression of the D antigen. Which of the following explains this observation?

  • The individual is homozygous for the d allele.
  • The individual inherited a D allele in _cis_ to a C allele.
  • The C antigen is dominant and suppresses D antigen expression.
  • The D allele is inherited in _trans_ to the allele carrying the C gene. (correct)

Which characteristic of Anti-D antibodies is correct?

<p>They do not bind complement, causing extravascular hemolysis. (A)</p> Signup and view all the answers

Which type of anti-D reagent is most likely to produce a false positive reaction, especially in standard slide and rapid tube tests?

<p>High-protein-based anti-D reagent. (B)</p> Signup and view all the answers

What distinguishes genetic weak D from partial D variants in RhD antigen expression?

<p>Genetic weak D has weakened expression of all D epitopes, whereas partial D is missing some D epitopes. (B)</p> Signup and view all the answers

How does the Rh-associated glycoprotein (RhAG) influence Rh antigen expression, and where is the gene encoding RhAG located?

<p>RhAG is essential for Rh antigen expression and is encoded on chromosome 6. (D)</p> Signup and view all the answers

What is the primary molecular mechanism leading to the D negative phenotype in individuals?

<p>Homozygosity for deletion of the RHD gene. (A)</p> Signup and view all the answers

If an individual with a partial D phenotype is exposed to a complete D antigen, what immunological response is most likely to occur?

<p>The individual will produce antibodies against the D epitopes they lack. (C)</p> Signup and view all the answers

How many times does the Rh protein cross the red blood cell membrane, and where are its N- and C-termini located?

<p>12 times, both termini are within the cytosol. (D)</p> Signup and view all the answers

How does the Tippet theory explain the genetic control of Rh antigens, and how does it differ from earlier models?

<p>It suggests two loci, one responsible for the D antigen and another for the C/c and E/e antigens, a concept supported by molecular genetic studies. (C)</p> Signup and view all the answers

If an individual's red blood cells type as D+, C+, E-, c+, and e+, how would this be represented using the ISBT numerical terminology?

<p>RH: 1, 2, -3, 4, 5 (D)</p> Signup and view all the answers

What is a key distinction between the Fisher-Race and Wiener theories regarding the genetic inheritance of Rh antigens?

<p>Fisher-Race suggested three closely linked loci, while Wiener proposed a single gene locus with multiple alleles at that locus. (B)</p> Signup and view all the answers

Why is determining the weak-D status of an individual clinically important in blood banking?

<p>To ensure accurate Rh typing of donors and patients, as weak-D individuals may be considered Rh-negative if not tested properly, leading to potential sensitization. (B)</p> Signup and view all the answers

How many different genotypes are theoretically possible in the Rh system, considering the inheritance patterns of RHD and RHCE?

<p>36 (C)</p> Signup and view all the answers

Which of the following statements accurately describes a key difference between the Fisher-Race and Wiener nomenclatures for Rh blood groups?

<p>Wiener assumes a single gene produces multiple factors, while Fisher-Race assumes three genes control individual antigens. (D)</p> Signup and view all the answers

An individual is typed as Rh:1,-2,3,4,5 using the Rosenfield nomenclature. How would this be represented using the Wiener nomenclature?

<p>R2 (C)</p> Signup and view all the answers

According to the Fisher-Race nomenclature, the absence of the 'D' antigen is denoted by 'd'. Which statement accurately explains the genetic basis of this notation?

<p>The 'd' notation signifies the deletion or non-expression of the D gene, as there is no actual 'd' gene. (C)</p> Signup and view all the answers

An individual's red blood cells are typed as CDe using Fisher-Race nomenclature. What is the equivalent representation using Rosenfield nomenclature?

<p>Rh:1,2,-3,4,5 (D)</p> Signup and view all the answers

If a patient is documented as 'r' in Wiener nomenclature, what antigens are present on their red blood cells?

<p>c, e (D)</p> Signup and view all the answers

The Rh system was first recognized in a case report of:

<p>A hemolytic transfusion reaction. (A)</p> Signup and view all the answers

What antigen is found in 85% of the white population and is always significant for transfusion purposes?

<p>D (C)</p> Signup and view all the answers

How are weaker-than-expected reactions with anti-D typing reagents categorized?

<p>Weak D (B)</p> Signup and view all the answers

Cells carrying a weak-D antigen require the use of what test to demonstrate its presence?

<p>Indirect antiglobulin test (A)</p> Signup and view all the answers

How are Rh antigens inherited?

<p>Codominant alleles (C)</p> Signup and view all the answers

Biochemically speaking, what type of molecules are Rh antigens?

<p>Proteins (C)</p> Signup and view all the answers

Rh antibodies react best at what temperature (°C)?

<p>37 (D)</p> Signup and view all the answers

Rh antibodies are primarily of which immunoglobulin class?

<p>IgG (C)</p> Signup and view all the answers

Rh antibodies have been associated with which of the following clinical conditions?

<p>Erythroblastosis fetalis (A)</p> Signup and view all the answers

What do Rhnull cells lack?

<p>Rh antigens (C)</p> Signup and view all the answers

What antigen system is closely associated phenotypically with Rh?

<p>LW (D)</p> Signup and view all the answers

Anti-LW will not react with which of the following?

<p>Rhnull RBCs (C)</p> Signup and view all the answers

Convert the following genotypes from Wiener nomenclature to Fisher-Race and Rosenfield nomenclatures, and list the antigens present in each haplotype.

<p>RzR1 = DCE/DCe ryr = dCE/dce R1r = DCe/dce R2R0 = DcE/Dce</p> Signup and view all the answers

Which Rh phenotype has the strongest expression of D?

<p>D– (D)</p> Signup and view all the answers

Which of the following most commonly causes an individual to type RhD positive yet possess anti-D?

<p>Partial D (B)</p> Signup and view all the answers

An individual has the following Rh phenotype: D+C+E+c+e+. Using Fisher-Race terminology, what is their most likely Rh genotype?

<p>DCe/DcE (D)</p> Signup and view all the answers

Which of the following is the most common Rh phenotype in African Americans?

<p>Dce/dce (A)</p> Signup and view all the answers

Flashcards

Anti-Rhesus Antibodies

Original name for antibodies later identified targeting the LW antigen, not Rh.

Rh Inheritance Theories

Fisher-Race: Three linked genes (D/d, C/c, E/e). Wiener: One gene locus with multiple alleles.

Weak D Expression

Genetic variations that produce slightly different versions of the D antigen.

Two Rh Gene Loci

RHD and RHCE

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ISBT Numerical Terminology

D=RH1, C=RH2, E=RH3, c=RH4, e=RH5

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Rh Phenotype Control

Two genes (RHD and RHCE) control Rh phenotypes. RHD encodes the D antigen, and RHCE encodes the C/c and E/e antigens.

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Rh Protein Structure

Rh proteins span the RBC membrane 12 times, creating six extracellular loops. Both N- and C-termini reside inside the cytosol. These proteins are not glycosylated but associate with RhAG.

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RhAG's Role

RhAG is a glycoprotein that's essential for expressing Rh antigens. Absence of RhAG leads to a lack of Rh antigen expression.

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D Antigen Importance

The D antigen is highly important in transfusion medicine. About 30% of D- recipients will produce Anti-D if exposed to D+ blood.

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D Negative Cause

The D negative phenotype often comes from being homozygous for the deletion of the RHD gene. Some D- individuals have an inactive RHD gene (RHD Ψ) that doesn't produce the D protein.

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"C in trans" effect

When the C allele is on the opposite chromosome from the D gene (Dce/dCe), it can lead to weak D antigen expression.

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Clinical significance of Anti-D

Anti-D can cause severe hemolytic transfusion reactions (HTRs) and hemolytic disease of the fetus and newborn (HDFN).

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Preventing Anti-D immunization

Administer Anti-D immunoglobulin to D-negative mothers within 72 hours of delivering a D-positive baby to prevent immunization.

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Anti-D detection method

The antibody screen test uses serum and D positive cells to detect Anti-D

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False Positive Anti-D Testing

False positives can result from these reagents.

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Rh Nomenclature Systems

Systems for describing Rh blood group genotypes.

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Wiener Nomenclature

Each Rh gene produces multiple factors (antigens).

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Fisher-Race Nomenclature

Three linked genes (C, D, E) control antigen production.

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Rosenfield Nomenclature

Numerical system to describe Rh antigens (e.g., Rh1 for D).

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R1 (Wiener)

Presence of C, D, and e antigens; absence of c and E.

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Study Notes

False Reactions with Rh Typing Reagents

False-Positives

  • Heavy cell suspension can cause false positives
  • Adjust the suspension to proper concentration, then retype
  • Cold agglutinins can cause false positives
  • Wash with warm saline, then retype
  • Extended incubation or drying of the test slide can cause false positives
  • Follow the manufacturer's instructions precisely
  • Rouleaux formation can cause false positives
  • Use saline-washed cells, then retype
  • Fibrin interference can cause false positives
  • Use saline-washed cells, then retype
  • Contaminating low-incidence antibody in reagent can cause false positives.
  • Try another manufacturer's reagent or use a known serum antibody
  • Polyagglutination can cause false positives
  • See chapter on polyagglutination
  • Bacterial contamination of reagent vial can cause false positives
  • Open a new vial of reagent, then retype
  • Using an incorrect reagent can cause false positives.
  • Repeat the test carefully, ensuring to read the vial label carefully

False-Negatives

  • Immunoglobulin-coated cells (in vivo) can cause false negatives
  • Use saline-active typing reagent
  • Saline-suspended cells (slide) can cause false negatives
  • Use unwashed cells
  • Deviation from manufacturer's directions can cause false negatives
  • Review the directions and repeat the test precisely
  • Omission of reagent manufacturer's directions
  • Always add reagent first and double-check before adding cells
  • Over vigorous resuspension can cause false negatives
  • Ensure the cells are gently resuspended in all tube test
  • Incorrect reagent selection can cause false negatives
  • Carefully read the vial label; repeat
  • Variant antigen can cause false negatives
  • Refer the sample for further investigation if variant antigen is suspected
  • Reagent deterioration can cause false negatives
  • Open a new vial and retest, if reagent deterioration is suspected </existing_notes>

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Rh Blood Group System PDF

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