Positive predictive value of anti-HCMV IgM as an index of primary infection.

A search for specific IgM antibodies was used for the detection of primary human cytomegalovirus (HCMV) infections, but the significance of the results is limited by the possible persistence of specific IgM over time, the fact that they are also produced during episodes of reactivation or reinfection, and possible cross-reactions with other viruses. Anti-HCMV antibody screening was carried out to assess the positive predictive value of detecting specific IgM antibodies using IgG and IgM enzyme-linked immunosorbent assays (ELISAs) in 6990 patients examined during the period 2005-2007. In comparison with IgG avidity, the positive predictive value of screening by IgM ELISA alone was 49.3%, which increased to 73% when the presence of IgM was confirmed by an enzyme-linked fluorescent assay (ELFA). The predictive values of highly or weakly positive IgM ELISA alone were respectively 68.8% and 16.4%, but increased to 83.1% and 39.1% if IgM was confirmed by ELFA. The positive predictive value of the IgM/IgG ratio ranged from 26.7% for a low ratio and the detection of IgM by ELISA alone, to 90.7% for a high ratio and ELFA-confirmed IgM detection. These findings indicate that a specimen in which highly positive IgM ELISA values are confirmed by ELFA, or which shows a high IgM/IgG ratio, is a good indicator of infection occurring within the previous three months.