Determination of rubella immunity by latex agglutination: its place in clinical routines.

The sensitivity and specificity of Rubascan (r) (RSC), a new latex agglutination test for rubella antibodies, was compared with those of the single radial hemolysis (SRH) and hemagglutination inhibition (HI) tests. We found RSC to have a sensitivity versus SRH and HI of 90-95% and 70-72%, respectively. RSC had a specificity versus SRH and HI of 97-100% and 96-100%, respectively. However, only 4/7 titer rises from cases of acute rubella or rubella vaccinations were clearly discernible in RSC. Moreover, only 2/10 anti-rubella IgG and IgM containing sera were RSC positive after protein A absorption although 10/10 were still HI positive. Additionally, the HI-positive IgM fractions from a sucrose density gradient centrifugation of an anti-rubella IgM containing serum were negative. We conclude that IgM reacts differently from IgG in RSC. We consider RSC a potentially useful reagent for determination of immunity in non-acute situations, and in non-pregnant persons like in pre-employment testing. This could be performed by relatively untrained personnel. On the other hand a rubella immunity test in pregnant women or in acute rubella should preferably be truly quantitative, in order to allow precise titer comparisons. In these cases, the interpretation of tests may require experience, and they should be performed at more specialized laboratories.