Diagnosis: Transplantation: Alloantibody Testing
• Traditionally, the method used for antibody detection was the complement-dependent cytotoxicity (CDC) assay.
• In recent years, solid-phase assays (SPAs) have been introduced as methods for human leukocyte antigen (HLA) antibody screening. Luminex is a SPA that consists of a series of polystyrene microspheres (beads) that are fluorochrome labeled and coated with mixtures of or individual HLAs. On incubation with a patient serum, alloantibodies directed against the coated antigens are deposited on the beads and are detected with a secondary (laser-excitable) fluorochrome-conjugated reagent.
• The detection of antibody deposition on specific beads (coated with known HLAs) indicates the specificity of the antibodies present.
• The intensity of the emission spectrum (read as mean fluorescence intensity [MFI]) gives information about the quantity of antibody present in the serum tested.
• The MFI quantification can reveal antibodies that are present in very low amounts and that would not be able to cause donor cell lysis in a CDC crossmatch or yield a positive reaction in flow cytometry (FC) crossmatching.
• SPA does not yield any qualitative information about the antibodies detected (most importantly, the complement fixing ability).
