BB_Lecture 3-Rh BLOOD GRP (1)

Rh Blood Group System Overview

ISBT Number: 004ISBT Name: RhChromosome: 1Number of Antigens: 61

Key Characteristics of the Rh Blood Group

  • "Rh" primarily refers to the D antigen.

  • A complex blood group system with over 50 different antigens.

  • Rh Antibodies (Abs): Produced only after exposure to foreign RBCs, leading to Hemolytic Disease of the Newborn (HDN) and Hemolytic Transfusion Reactions (HTR).

  • Immunogenicity of Rh antigens (ranked): D > c > E > C > e.

Terminologies in Rh Blood Group System

  • Fisher-Race (DCE): D, C, E, c, e

  • Wiener (Rh-Hr): Rho, rh’, rh’’, hr’, hr’’

  • Rosenfield (Alphanumeric): Rh1, Rh2, Rh3, Rh4, Rh5

  • ISBT (Numeric): 004001, 004002, 004003, 004004, 004005

Genetic Inheritance of Rh

  • Fisher-Race Theory: Consists of three closely linked genes at different loci (D, C/c, E/e). Autosomal Codominant Inheritance; example: Dce/DCE individuals show full antigen expression.

  • Wiener Theory: States Rh antigens derive from one gene coding for agglutinogen with multiple factors. Chromosome designations: Rº = Rh, Rho, hr1, hrII.

  • Rosenfield Notation: Assigns numbers to antigens (D=Rh1, C=Rh2, E=Rh3).

  • ISBT Numbering System: Numeric system for antigen identification.

  • Tippett Theory (2 Subloci): Two Rh genes control Rh antigens; RHD codes D antigen, RHCE codes combinations of CE/c, ce/C, cE.

Molecular Basis of Rh Antigens

  • RHAG Gene: Located on chromosome 6; mutations result in missing RhD/RhCE proteins.

  • Proteins: Non-glycosylated proteins integral to RBC membranes, maintaining structural integrity.

D Antigen Characteristics

  • Highly immunogenic; Rh negative individuals lack RhD completely.

  • Minimal exposure to Rh positive RBCs (>0.1mL) can provoke antibody production.

Typing and Reagents for Rh Blood Group

  • Routine Typing: Generally tests only for D antigen.

  • Rh Typing Reagents include High-Protein Anti-D and Monoclonal Reagents.

Clinical Considerations

  • Transfusion Reactions: Rh-mediated reactions lead to extravascular destruction of Ab-coated RBCs.

  • Hemolytic Disease of the Fetus and Newborn (HDFN): Maternal anti-D antibodies cross placenta, destroying fetal RBCs.

Weak D and Variations in D Ag Expression

  • Weak D is detectable through Indirect Antiglobulin Test (IAT); variations include Partial D, Del.

Summary

The Rh blood group system is crucial for transfusion medicine and pregnancy management. Understanding its complexities ensures safe clinical practice.