Effect of serum-antigen incubation times on the expression of non-specific inhibitors of rubella hemagglutination.

Under certain conditions, serum very low-density lipoproteins (VLDL) and high-density lipoproteins (HDL) can inhibit rubella hemagglutination. The level of this non-specific hemagglutination-inhibition (HI) activity increases as the incubation period between serum and antigen is increased. Treatment of serum with heparin-MnCl2 does not precipitate HDL, and may not effect complete removal of all VLDL. This treatment method, therefore, should be considered a source of false-positive reactions, especially when extended serum-antigen incubation periods are used to enhance HI activity and to detect low levels of IgM.