Indirect Antiglobulin Test (IAT)
Definition
A two-stage serological test in which IgG antibody is incubated with red cells, unbound antibody is washed away, and anti-human globulin (Coombs reagent) is added to cross-link IgG-coated cells into visible agglutination. Required to detect weak D and other low-expression Rh antigens.
- Abbreviation
- IAT
- Stages
- Two: antibody incubation, then Coombs reagent addition
- Reagent
- Anti-human globulin (Coombs reagent)
- Key use
- Detecting weak D and low-expression Rh antigens
Common questions
Why is a wash step required between the two stages of the indirect antiglobulin test?+
Unbound IgG antibody left in solution would consume the anti-human globulin reagent before it can cross-link the antibody actually bound to the red cells, so washing away free antibody is necessary for the test to give a clean, interpretable result.
How does the IAT differ from the direct antiglobulin test used in forensic serology?+
The IAT detects antibody that has been incubated with cells in vitro, such as testing an antiserum's reactivity, while the direct test detects antibody already bound to cells in vivo, so the two answer different questions despite sharing the same Coombs reagent.
Related terms
- CDE Nomenclature (Fisher-Race)
- The modern standard notation for Rh antigens, naming three antithetical pairs: C/c, D (no d), and E/e. Haplotypes such as CDe (R1),...
- D Antigen
- The most immunogenic Rh antigen, encoded by the RHD gene. Its presence defines Rh-positive; its absence defines Rh-negative. No naturally occurring anti-D...
- Rh-Hr Nomenclature (Wiener)
- An earlier notation system using alphanumeric agglutinogen codes (R0, R1, R2, Rz, r, r', r'', ry) for Rh haplotypes. Wiener's R1 corresponds...
- RHD Genotyping
- PCR-based molecular typing of the RHD gene to determine D antigen status from DNA, including from dried biological evidence where serological red...
- Weak D (Formerly Du)
- A reduced-expression variant of the D antigen that does not agglutinate red cells with standard IgM anti-D reagent in the direct test...