Hemadsorption immunosorbent technique for determination of rubella immunoglobulin M antibody

A highly specific and sensitive hemadsorption immunosorbent technique for measuring rubella immunoglobulin M (IgM) antibody is described. IgM from human sera was absorbed into anti-human IgM-coated wells in plates and rubella-specific IgM was detected by adding rubella virus hemagglutinin and a small quantity of sheep erythrocytes. Centrifugation of the plates facilitated reading of the test. Specific IgM-positive sera showed hemadsorption, whereas negative sera showed hemagglutination. Rheumatoid factor and rubella-specific IgG antibody did not interfere with the results. The test was clearly more sensitive than the solid-phase immunosorbent technique for detection of rubella IgM antibody by hemagglutination inhibition and at least as sensitive as the hemagglutination inhibition test on IgM fractions from a sucrose density gradient and the indirect immunofluorescence test for IgM antibody with absorbed serum. All of 40 sera from 17 rubella patients taken 4 to 49 days after the onset of rash were positive in the new test, with antibody titers ranging from 2,560 to 81,920 between 4 and 28 days. The test is reliable, practical, and suitable for general diagnostic use.