Q.4 Identification of blood groups involves
(A) precipitation (B) neutralization
(C) opsonization (D) agglutination

Blood group identification relies on agglutination, where antibodies cause clumping of red blood cells bearing matching antigens, making (D) the correct answer. This visible reaction forms the basis of ABO and Rh typing in transfusions and forensics.​

Correct Answer

The correct option is (D) agglutination. Specific antibodies (anti-A, anti-B, anti-D) bind surface antigens on erythrocytes, cross-linking cells into visible clumps under microscopy or naked eye. Agglutination confirms antigen presence: e.g., anti-A causes clumping in group A blood.​

Option Explanations

Blood typing uses forward (cell antigens) and reverse (serum antibodies) agglutination; other processes serve different immune roles.

• (A) Precipitation: Incorrect; soluble antigen-antibody complexes form lattices in fluids, used in immunodiffusion, not cell clumping.​

• (B) Neutralization: Incorrect; antibodies block viral toxins or receptors (e.g., antitoxin), preventing activity without clumping.​

• (C) Opsonization: Incorrect; antibody Fc regions coat pathogens for phagocytosis, enhancing engulfment, not identification via aggregates.​

• (D) Agglutination: Correct; multivalent IgM/IgG bridge erythrocytes, causing rapid visible clumping for ABO/Rh typing.​

Mechanism Overview

In slide/tube tests, blood cells mix with antisera; matching antigens trigger IgM-mediated hemagglutination (larger clumps) or IgG (microscopic). No reaction indicates absence (e.g., group O lacks A/B). Coombs test detects incomplete IgG agglutination.​