Multicenter evaluation of a 1-h enzyme-linked immunosorbent assay for rubella serology

A 1-h enzyme-linked immunosorbent assay (Rubestat) was developed for rubella virus immunoglobulin G detection. The assay used phenolphthalein monophosphate as the substrate, which, when developed, can easily be read visually. Rubestat compared very favorably to hemagglutination inhibition and commercial enzyme-linked immunosorbent assays in its ability to determine immune status. Rubestat demonstrated greater than 97% specificity, sensitivity, and accuracy as compared with other methodologies at 10 different laboratories. The Rubestat index values were precise, with coefficients of variation for intra- and interassay variation of less than 10%. Mean index values had a linear correlation with hemagglutination inhibition titers (r2 greater than 0.97). A population distribution of index values illustrated two distinct bell-shaped curves representing the positive and negative populations. Studies of acute and convalescent serum pairs showed Rubestat to be as accurate as hemagglutination inhibition in determining seroconversion.