Stability of total and rubella-specific IgG in oral fluid samples: the effect of time and temperature

Oral fluid (saliva) samples are increasingly used as a minimally invasive alternative to serum to detect antibody for viral diagnostics and population-based surveys of immunity to common infections. Postal collection of these samples is convenient, but it is uncertain how oral fluid antibody levels may deteriorate during transit. In this study multiple oral fluid samples, from a group of individuals, were collected and kept at two different temperatures (10 and 20 degrees C, simulating winter and summer conditions ) for periods of up to 7 days. They were then tested for total immunoglobulin G (IgG) and for rubella-specific IgG. Total IgG concentrations ranged from 2.0 to 48.6 mg/l but showed no significant decrease over the 7-day period. There was also no significant change in rubella-specific IgG measured using an antibody capture ELISA, but testing with an indirect rubella IgG ELISA revealed a significant decrease in absorbance values between day 1 and day 7 at 20 degrees C. The difference in the rubella assay results may reflect the different assay formats with the signal in the indirect procedure related to the concentration of rubella IgG in the oral fluid sample, rather than the proportion of virus-specific IgG measured with the antibody capture format. The study demonstrated that total and rubella specific IgG in oral fluid samples were stable for up to 7 days at differing temperatures and that an antibody capture assay format should be used for virus-specific testing to minimise inaccurate results due to low IgG concentrations in oral fluid samples.