Comparison of several test systems used for determination of rubella immune status

Hemagglutination inhibition (HAI) is currently the most widely used technique for the determination of rubella immune status. However, two new methods, enzyme-linked immunosorbent assay (ELISA) and indirect immunofluorescence (FIAX), have also been adapted for this purpose. In comparing a commercially available ELISA system (BIO-BEAD, Litton Bionetics) with an HAI system (RUBA-tect, Abbott Laboratories), some ELISA-positive sera were found to be rubella antibody negative by the HAI system. To determine which of these results more accurately reflected the immune status of the patient, 74 RUBA-tect-negative sera were retested by ELISA BIO-BEAD, FIAX (International Diagnostic Technology) and by modified HAI, employing fresh erythrocytes (using Flow Laboratories reagents). Eleven RUBA-tect-negative sera (15%) were positive by ELISA, FIAX, and modified HAI. Two sera were positive only by ELISA and FIAX, two sera were positive by ELISA and HAI, four sera were positive by ELISA only, and one serum was positive by FIAX only. Neutralization assays were subsequently performed on sera positive by only one or two of the procedures to determine the presence of protective rubella antibodies in these sera; all but three of the sera were positive for neutralizing antibody. Commercial ELISA and FIAX systems appear to be more sensitive indicators of rubella immune status than are commercial HAI kits which use stabilized erythrocytes. Neither ELISA nor FIAX require extraction of serum; moreover, the ELISA BIO-BEAD test assay can be performed without an expensive instrument for reading.