Rh Blood Group System

Dr. Topesh Patle

Introduction

  • Rh blood group system is the second most important blood group system after ABO.

  • It is highly polymorphic, with more than 50 antigens identified.

  • Clinically most significant antigen: D antigen

  • Major importance in:

    • Blood transfusion reactions

    • Hemolytic disease of fetus and newborn (HDFN)

  • Rh antigens are protein antigens, unlike carbohydrate ABO antigens.

  • Present only on red blood cells, not in body secretions.

History 

  • Discovered in 1940 by Karl Landsteiner and Alexander Wiener

  • Rabbits were immunized with Rhesus monkey red cells

  • Resulting antibodies agglutinated human red cells

  • Initially believed to be same antigen; later clarified as different but related

  • Explained:

    • Severe transfusion reactions

    • Erythroblastosis fetalis

  • The term “Rh factor” became widely accepted.

 

Genetics 

  • Genes located on chromosome 1 (1p36.11)

  • Controlled by two closely linked genes:

    • RHD gene → codes for D antigen

    • RHCE gene → codes for C/c and E/e antigens

  • Genes are inherited as a haplotype

  • Rh positivity depends on presence of RHD gene

  • Rh negativity usually due to complete deletion of RHD gene

  • Unlike ABO:

    • No naturally occurring antibodies

    • Antibodies develop only after exposure

 

Molecular Genetics of Rh System

  • RHD and RHCE genes encode transmembrane proteins

  • Proteins have:

    • 10–12 membrane-spanning segments

    • Intracellular and extracellular loops

  • Small amino acid substitutions cause:

    • Weak D

    • Partial D

    • Other Rh variants

  • Rh proteins are closely associated with:

    • Rh-associated glycoprotein (RhAG)

  • Normal Rh antigen expression requires:

    • Functional RHD/RHCE

    • Functional RhAG gene

 

Nature of Rh Antigens

  • Rh antigens are:

    • Proteins

    • Heat stable

    • Enzyme sensitive

  • Fully developed at birth

  • Not present in saliva or body fluids

  • Strongly immunogenic:

    • D antigen is one of the most immunogenic antigens known

  • Do not activate complement efficiently

  • Antibody-coated cells are removed by extravascular hemolysis

 

D Antigen

  • Most important antigen in Rh system

  • Present in ~85% of population

  • Highly immunogenic:

    • 1 unit transfusion → ~80% chance of sensitization

  • Presence defines Rh positive

  • Absence defines Rh negative

  • Primary cause of:

    • Severe transfusion reactions

    • HDFN

 

Weak D (Du Antigen)

  • Reduced expression of D antigen on RBC surface

  • Caused by:

    • Amino acid substitutions in transmembrane region

  • Not detectable by immediate spin testing

  • Detected by:

    • Indirect Antiglobulin Test (IAT)

  • Characteristics:

    • D antigen complete but quantitatively reduced

    • Usually do not form anti-D

  • Blood bank significance:

    • Donors → treated as Rh positive

    • Recipients → often treated as Rh negative (policy dependent)

 

Partial D Antigen

  • D antigen is qualitatively incomplete

  • One or more D epitopes are missing

  • Caused by:

    • Hybrid RHD–RHCE genes

  • Individuals may:

    • Type as Rh positive

    • Still produce anti-D when exposed

  • Very important in:

    • Pregnancy

    • Transfusion medicine

  • Treated as Rh negative recipients

 

Other Variants of Rh System

  • Includes:

    • Cw, Cx, Ew

    • Del phenotype

    • Hybrid Rh antigens

  • Common in certain ethnic groups

  • Often undetected by routine serology

  • Require:

    • Advanced serological testing

    • Molecular genotyping

  • Can cause:

    • Unexpected alloimmunization

    • Delayed hemolytic reactions

 

Rh-Null Phenotype

  • Complete absence of all Rh antigens

  • Extremely rare

  • Two types:

    • Amorph type – deletion/inactivation of RHD & RHCE

    • Regulator type – mutation in RhAG gene

  • Clinical features:

    • Mild to moderate hemolytic anemia

    • Stomatocytosis

    • Increased RBC fragility

  • Transfusion problems:

    • Only Rh-null blood compatible

  • Demonstrates structural importance of Rh proteins

 

Rh Antibodies

  • Not naturally occurring

  • Formed only after:

    • Transfusion

    • Pregnancy

  • Belong to IgG class

  • Cross placenta easily

  • Common antibodies:

    • Anti-D (most significant)

    • Anti-C

    • Anti-E

    • Anti-c

  • Cause:

    • Hemolytic transfusion reactions

    • HDFN

  • Best detected by:

    • Indirect Coombs test

Factors Influencing Rh Immunization

  • Volume of antigen exposure

  • Immunogenic strength of antigen

  • Route of exposure:

    • Transfusion > pregnancy

  • Genetic makeup of recipient

  • ABO incompatibility:

    • Reduces Rh immunization

  • Frequency of exposure

  • Use or absence of anti-D prophylaxis

Functional Role of Rh Antigens

  • Not only blood group markers

  • Act as:

    • Ammonia transport channels

    • CO₂ transport facilitators

  • Maintain:

    • Red cell membrane stability

    • Cell shape and deformability

  • Loss of Rh proteins leads to:

    • Membrane defects

    • Reduced RBC survival

  • Explains anemia seen in Rh-null individuals

 

Clinical Significance of Rh System

  • Essential in:

    • Blood grouping

    • Cross-matching

    • Antenatal screening

  • Anti-D prophylaxis prevents:

    • HDFN

    • Maternal sensitization

  • Molecular Rh typing improves:

    • Transfusion safety

    • Management of complex cases

 

MCQs

1. The Rh blood group system was discovered in:

A. 1935
B. 1937
C. 1940
D. 1945

Answer: C. 1940

2. Discovery of Rh system is credited to:

A. Landsteiner and Levine
B. Wiener and Coombs
C. Landsteiner and Wiener
D. Ehrlich and Pauling

Answer: C. Landsteiner and Wiener

3. Rh blood group system is second in importance after:

A. Kell
B. ABO
C. Lewis
D. Duffy

Answer: B. ABO

4. The most immunogenic antigen of Rh system is:

A. C
B. c
C. E
D. D

Answer: D. D

5. Rh antigens are chemically:

A. Carbohydrates
B. Glycolipids
C. Proteins
D. Lipopolysaccharides

Answer: C. Proteins

6. Rh antigens are located on:

A. Plasma proteins
B. Platelets
C. Red cell membrane
D. Leukocytes

Answer: C. Red cell membrane

7. Genes controlling Rh system are located on chromosome:

A. 6
B. 9
C. 1
D. 19

Answer: C. 1

8. RHD gene encodes which antigen?

A. C
B. E
C. D
D. c

Answer: C. D

9. RHCE gene encodes which antigens?

A. D only
B. C and D
C. C/c and E/e
D. D and E

Answer: C. C/c and E/e

10. Rh-negative phenotype is usually due to:

A. Suppressed gene expression
B. Mutation of RHCE gene
C. Deletion of RHD gene
D. Absence of RhAG protein

Answer: C. Deletion of RHD gene

11. Naturally occurring antibodies are:

A. Present in Rh system
B. Absent in Rh system
C. IgM type
D. Cold reacting

Answer: B. Absent in Rh system

12. Rh antibodies are usually of which class?

A. IgM
B. IgA
C. IgE
D. IgG

Answer: D. IgG

13. Rh antibodies are formed after:

A. Birth
B. Infection
C. Sensitization
D. Vaccination

Answer: C. Sensitization

14. Which Rh antibody most commonly causes HDFN?

A. Anti-E
B. Anti-C
C. Anti-c
D. Anti-D

Answer: D. Anti-D

15. Weak D antigen is best detected by:

A. Immediate spin test
B. Saline method
C. Indirect antiglobulin test
D. Enzyme test

Answer: C. Indirect antiglobulin test

16. Weak D is caused by:

A. Missing D epitopes
B. Reduced antigen expression
C. Absence of D gene
D. ABO incompatibility

Answer: B. Reduced antigen expression

17. Individuals with weak D usually:

A. Produce anti-D
B. Do not produce anti-D
C. Always Rh negative
D. Have Rh-null phenotype

Answer: B. Do not produce anti-D

18. Partial D individuals may produce:

A. Anti-E
B. Anti-c
C. Anti-D
D. Anti-A

Answer: C. Anti-D

19. Partial D occurs due to:

A. Quantitative reduction
B. Hybrid gene formation
C. Gene deletion
D. RhAG mutation

Answer: B. Hybrid gene formation

20. Del phenotype is characterized by:

A. Absence of Rh antigens
B. Very weak D expression
C. Complete D antigen
D. Excess D antigen

Answer: B. Very weak D expression

21. Rh-null phenotype lacks:

A. Only D antigen
B. Only C and E antigens
C. All Rh antigens
D. ABO antigens

Answer: C. All Rh antigens

22. Rh-null individuals commonly show:

A. Polycythemia
B. Leukopenia
C. Hemolytic anemia
D. Thrombocytopenia

Answer: C. Hemolytic anemia

23. Rh-null regulator type is due to mutation in:

A. RHD gene
B. RHCE gene
C. RhAG gene
D. Kell gene

Answer: C. RhAG gene

24. RhAG protein is essential for:

A. ABO expression
B. Rh antigen expression
C. Platelet function
D. Complement activation

Answer: B. Rh antigen expression

25. Rh antigens are fully developed:

A. At 6 months
B. At 1 year
C. At birth
D. After puberty

Answer: C. At birth

26. Rh antigens are absent in:

A. Plasma
B. Saliva
C. Both A and B
D. Serum only

Answer: C. Both A and B

27. Main mechanism of hemolysis in Rh incompatibility is:

A. Intravascular
B. Complement mediated
C. Extravascular
D. Mechanical

Answer: C. Extravascular

28. Rh antibodies can cross placenta because they are:

A. IgM
B. IgA
C. IgE
D. IgG

Answer: D. IgG

29. ABO incompatibility reduces Rh sensitization because:

A. Rh antigens are destroyed early
B. Antibodies neutralize Rh
C. RBCs are cleared rapidly
D. Rh antibodies are IgM

Answer: C. RBCs are cleared rapidly

30. Most effective prevention of Rh immunization is:

A. Blood grouping
B. Cross matching
C. Anti-D immunoglobulin
D. Steroids

Answer: C. Anti-D immunoglobulin

31. Anti-D prophylaxis is given to:

A. Rh-positive mother
B. Rh-negative mother
C. Rh-positive fetus
D. Rh-null mother

Answer: B. Rh-negative mother

32. Rh proteins are primarily involved in transport of:

A. Oxygen
B. Sodium
C. Ammonia and CO₂
D. Glucose

Answer: C. Ammonia and CO₂

33. Absence of Rh proteins leads to:

A. Increased RBC lifespan
B. Membrane instability
C. Thrombosis
D. Leukocytosis

Answer: B. Membrane instability

34. Which Rh antigen is most common after D?

A. E
B. C
C. c
D. e

Answer: C. c

35. Rh system antibodies are best detected by:

A. Slide method
B. Tube saline method
C. Indirect Coombs test
D. Direct Coombs test

Answer: C. Indirect Coombs test

36. Rh antibodies are optimally reactive at:

A. 4°C
B. 22°C
C. 37°C
D. 60°C

Answer: C. 37°C

37. Which condition is most severe in Rh incompatibility?

A. ABO HDN
B. Rh HDN
C. Kell HDN
D. Lewis HDN

Answer: B. Rh HDN

38. Rh antigens do not activate complement efficiently because they are:

A. Carbohydrate
B. Protein antigens
C. Weak antigens
D. IgM mediated

Answer: B. Protein antigens

39. Which test is used to confirm Rh-null phenotype?

A. Slide test
B. Enzyme test
C. Molecular typing
D. Forward grouping

Answer: C. Molecular typing

40. Which Rh antigen variant poses maximum transfusion risk?

A. Weak D
B. Partial D
C. Del
D. Cw

Answer: B. Partial D

41. Rh blood group system consists of more than:

A. 10 antigens
B. 20 antigens
C. 30 antigens
D. 50 antigens

Answer: D. 50 antigens

42. Rh antibodies cause hemolysis mainly in:

A. Liver and spleen
B. Kidney
C. Blood vessels
D. Bone marrow

Answer: A. Liver and spleen

43. Rh antigen expression is restricted to:

A. All body cells
B. Epithelial cells
C. Erythroid cells
D. Platelets

Answer: C. Erythroid cells

44. Weak D differs from partial D because weak D is:

A. Qualitative defect
B. Quantitative defect
C. Complete absence
D. Gene deletion

Answer: B. Quantitative defect

45. Partial D individuals are treated as Rh-negative because they may:

A. Lack RhAG
B. Develop anti-D
C. Be Rh-null
D. Have ABO antibodies

Answer: B. Develop anti-D

46. Rh system inheritance is best described as:

A. Simple dominant
B. Simple recessive
C. Haplotypic inheritance
D. Codominant only

Answer: C. Haplotypic inheritance

47. Rh antibodies are detected during pregnancy by:

A. Forward grouping
B. Reverse grouping
C. Antibody screening
D. Cross match only

Answer: C. Antibody screening

48. Rh antigen density is highest on:

A. Fetal RBCs
B. Newborn RBCs
C. Adult RBCs
D. Reticulocytes

Answer: C. Adult RBCs

49. Rh incompatibility is most likely when mother is:

A. Rh positive
B. Rh negative
C. ABO incompatible
D. Rh-null

Answer: B. Rh negative

50. Rh blood group system is clinically important mainly because of:

A. Frequency
B. Molecular complexity
C. Immunogenicity
D. Secretor status

Answer: C. Immunogenicity