Evaluation of a novel immunoglobulin A capture enzyme immunoassay for diagnosis of cytomegalovirus infection in renal and heart transplant recipients.

In a retrospective cohort study of 68 organ transplant patients, the usefulness of a new commercial immunoglobulin A (IgA) antibody capture enzyme immunoassay (EIA) specific to human cytomegalovirus (CMV) for the early diagnosis of CMV disease was investigated. The results were compared with those obtained with the CMV pp65 antigen assay in peripheral blood leukocytes, an IgM immunoblot assay, and six other commercial EIAs. In 21 of 28 patients with CMV disease, the pp65 antigen assay and the immunoblot assay identified patients before the onset of disease more frequently than any other serological test method (17 and 13 patients, respectively; p = 0.0029). In patients at risk for primary CMV infection, the pp65 antigen assay was the only method that identified all patients prior to the onset of CMV disease (p = 0.008). For the other patients who were at risk for CMV infection, the pp65 antigen assay and the immunoblot assay detected infection before CMV disease more frequently than any other test system (p = 0.026). With respect to CMV disease, both immunoblotting and the pp65 antigen assay showed excellent sensitivity (100% and 89%, respectively). However, the specificity of the immunoblot was poor (41%), while the specificity of the pp65 antigen assay was reasonably good (68%). The IgA capture EIA showed moderate sensitivity (61%) and reasonable specificity (76%). In conclusion, the pp65 antigen assay, which detects pp65 antigen in leukocytes, is the method of choice for diagnosis of either primary or recurrent CMV infection. The specificity of the pp65 antigen assay was improved by additional testing for specific IgA and IgM antibodies (95% vs. 68%). The IgA assay is of limited value in renal and heart transplant patients, since it detected IgA antibodies only sporadically, and even then, too late for a timely therapy.