Single-serum diagnosis of rubella by combined use of the hemagglutination inhibition and passive hemagglutination tests.

We explored the feasibility of using the passive hemagglutination (PHA) test in combination with the hemagglutination inhibition (HI) test for the single-serum diagnosis of rubella. We found by sedimentation analysis of the serum that early 7S antibody produced within 1 month after the onset of the rash had high HI but much lower PHA titers, whereas the PHA titers of antibody produced later were slightly higher than the HI titers. (19S antibody in the early serum had some PHA activity.) This disparity between the HI and PHA activities of the early 7S antibody could be used for the routine diagnosis of rubella. A comparison of the HI titers of the test serum with the PHA titers of mercaptoethanol-treated serum constitutes a simple method for determining whether the serum sample was taken shortly or remotely after the infection.