Antibody Detection and Identification
Screening strategy
Antibody detection begins with 2-3 group O reagent screen cells chosen to be homozygous for clinically significant antigens so dosage is expressed, and negative for nuisance low-incidence antigens. Methods include tube testing (immediate spin, 37 C, AHG), column agglutination gel, and solid phase; potentiators such as LISS shorten incubation while PEG enhances sensitivity but increases false positives from rouleaux and protein.
The logic of rule-out and rule-in
An antibody is ruled out when every cell negative for the corresponding antigen is also nonreactive. Ideally you exclude with three antigen-negative cells; two is the practical minimum. Rule in by matching reactivity to one antigen across a panel, then confirming with selected cells and by phenotyping the patient. Phenotyping after recent transfusion is unreliable because donor cells circulate; use genotyping or adsorption instead. Enzyme panels, DTT-treated cells (which destroy Kell, Lutheran, and Dombrock and are used to bypass anti-CD38 interference from daratumumab), and neutralization with saliva or soluble Lewis substance resolve multiple or interfering antibodies.
Common traps
- Panagglutination: warm or cold autoantibody, rouleaux, contaminated reagents. Autologous adsorption for warm autoantibodies, allogeneic adsorption after phenotyping when the patient has been transfused.
- Evanescent antibodies: anti-Jka can fall below detection and return days later as a delayed hemolytic reaction, so check historical records.
- Dosage: heterozygous cells may miss anti-Jka, anti-Fya, or anti-M.
- Room-temperature-only reactivity still requires 37 C/AHG testing before being dismissed as insignificant.
Worked example: serum reacts 2+ with all panel cells at AHG and the autocontrol is negative. If the patient's phenotype is Jk(a+b-) and E-negative, anti-Jkb and anti-E remain possible while anti-Jka and anti-e are excluded; selected homozygous Jkb-positive and E-positive cells plus a Jkb-negative, E-negative cell confirm or exclude each specificity.