Cytomegalovirus antigenic heterogeneity can cause false-negative results in indirect hemagglutination and complement fixation antibody assays.

Cord sera and antepartum maternal sera from three congenitally cytomegalovirus (CMV)-infected infants and their mothers were CMV seronegative (titer, less than 8) in a complement fixation (CF) assay with a glycine-extracted CMV AD169 antigen; sera from two of the infants and mothers were also seronegative in a commercial indirect hemagglutination (IHA) assay with AD169 antigen. In tests with their own CMV isolates propagated and made into glycine-extracted CF antigen, all were seropositive. When 108 random cord sera were assayed for CF antibody with AD169, Davis, and A antigens (A is a locally derived antigen from one of the above infants), 44 were seropositive and 54 were seronegative for all three antigens. Of the remaining 10 sera, 4 were positive for A only, 3 were positive for A and Davis only, 2 were positive for Davis and AD169 only, and 1 was positive for AD169 only. All 10 were positive when a mixture of all three antigens was used. The IHA assay with AD169 antigen was positive with only 4 of these 10 sera. These results suggest that up to 6% of sera may be misclassified as seronegative in the CF and IHA assays if only a single antigen is used.