ABO Blood Group System
Definition
The system of A and B antigens on red cell surfaces, described by Landsteiner in 1901 and typed by naturally occurring anti-A and anti-B antibodies. The first repeatable biological marker available for forensic blood classification.
- Basis
- Presence/absence of A and B antigens on red cell membranes
- Gene location
- ABO locus on chromosome 9
- Forensic role
- Exclusionary screening, superseded by DNA for individualisation
- Secretor status
- Determines if ABO antigens appear in saliva, semen and other fluids
Common questions
Why is ABO typing no longer used to identify a suspect?+
ABO typing only sorts individuals into four broad groups, so it cannot individualise a stain to one person. It remains useful for quickly excluding a suspect whose blood type does not match a stain, but STR DNA profiling has replaced it for identification.
What is secretor status and why does it matter for body fluid evidence?+
Roughly 80% of people are secretors, meaning their ABO antigens appear in saliva, semen, and other body fluids as well as blood. Non-secretors do not shed ABO antigens into these fluids, which limits what ABO testing alone can reveal from a saliva or semen stain.
Is ABO typing still used anywhere in modern casework?+
It occasionally supplements DNA results in mixed-stain interpretation or in historical case reviews where only serological typing was originally performed, but it is not a primary identification method in current practice.
Related terms
- Enzyme-Linked Immunosorbent Assay (ELISA)
- An immunoassay format in which an enzyme-conjugated antibody produces a measurable colour change on substrate addition. Developed in 1971, adopted in forensic...
- Lateral-Flow Immunoassay
- A point-of-care competitive immunochromatographic format on a nitrocellulose strip. In the absence of drug, colloidal gold-labelled antibody is captured at a test...
- Monoclonal Antibody
- An antibody produced from a single B-cell clone, recognising a single specific epitope. In forensic species identification, monoclonal antibodies offer higher specificity...
- Precipitin Test
- A serological method in which an antiserum specific to one species' proteins is mixed with an extract of an unknown specimen. Formation...
- Radioimmunoassay (RIA)
- An immunological quantification method developed in the late 1950s in which a radiolabelled antigen competes with unlabelled antigen for antibody binding sites....