Agglutination
Definition
Clumping of red cells that occurs when antibodies in serum bind to incompatible antigens on the cell surface, cross-linking cells into visible aggregates. The basis of direct ABO typing.
- Observable endpoint
- The basis and endpoint of direct ABO typing and all classical blood-grouping tests.
- Mechanism
- Antibodies cross-link red blood cell surface antigens into visible aggregates.
Common questions
What does agglutination look like in a blood grouping test?+
You see visible clumping or aggregation of red blood cells. When antibodies in the test serum find matching antigens on the red cell surface, they bind and cross-link the cells together, creating clumps that are easy to spot with the naked eye.
Why is agglutination important in forensic blood typing?+
Agglutination is the actual endpoint you read in classical blood grouping techniques. The visible clumping tells you whether a bloodstain's antigens match the antibodies in your test serum, which is how you determine its blood group.
When do red blood cells agglutinate?+
Agglutination happens when antibodies encounter red blood cells with incompatible antigens on their surface. The antibodies bind to the antigens and pull multiple cells together, forming the clumps that indicate a positive test result.
Related terms
- Antigen
- A molecule recognised by the adaptive immune system through specific binding to an antibody or T-cell receptor. Defined by immunogenicity (capacity to...
- Secretor Status
- A genetic trait that determines whether a person expresses their ABO blood group antigens in secreted body fluids such as saliva, semen,...
- ABO System
- The blood-group classification described by Karl Landsteiner in 1901: groups A, B, AB, and O, defined by antigens on red-cell surfaces and...
- Absorption-Elution
- A technique for detecting antigens on dried red cell debris. Specific antiserum is absorbed onto the stain; if the antigen is present,...
- Absorption-Inhibition
- A known volume of antiserum is exposed to the stain; the residual unbound antibody is then titrated against indicator cells. A drop...
- Antibody (Isohaemagglutinin)
- An immunoglobulin in plasma directed against red-cell antigens the host does not carry. Group O serum carries anti-A and anti-B; group AB...
- Antiserum
- Serum collected from an immunised animal containing antibodies directed against a specific antigen or group of antigens. In species identification, antiserum raised...
- Bombay Phenotype (Oh, Hh)
- Y. M. Bhende, 1952, K.E.M. Hospital Mumbai. Homozygous absence of the H antigen, so neither A nor B can be expressed; types...
- Forensic Serology
- The branch of forensic science concerned with detecting and characterising biological fluids (blood, semen, saliva, vaginal secretions) as evidence in legal proceedings,...
- Glycosyltransferase
- The enzyme encoded by the ABO gene locus that attaches terminal sugar residues to the H antigen chain. Group A transferase adds...
- H Antigen
- A fucose-containing oligosaccharide on red cell surfaces and secreted epithelial cells, produced by FUT1 (on red cells) and FUT2 (in secretions). It...
- ISBT
- International Society of Blood Transfusion. The authority that catalogues and numbers the 35+ recognised blood group systems.
Explained in these topics
- ABO System: Biology and Forensic HistoryClumping of red cells that occurs when antibodies in serum bind to incompatible antigens on the cell surface, cross-linking cells into visible aggregates. The...
- Blood Group Systems in Forensic Science: ABO, Rh, MNS and BeyondVisible clumping of red cells when their surface antigen meets a matching antibody. The endpoint of every classical blood-grouping test.
- Techniques for Determining Blood Groups from BloodstainsVisible clumping of red cells when their surface antigens cross-link with matching antibodies. The endpoint every classical grouping technique reads.