Cytomegalovirus and beta 2 microglobulin in urine specimens. Reciprocal interference in their detection is responsible for artifactually high levels of urinary beta 2 microglobulin in infected transplant recipients.

We have previously shown that the binding of host beta 2 microglobulin (beta 2 m) by cytomegalovirus (CMV) in body fluids masks the viral antigenic determinants preventing its detection by CMV-specific monoclonal antibodies. We now report that the recognition of CMV-bound beta 2m by anti-beta 2m-specific antibodies in assays for beta 2m, results in erroneously high readings for beta 2m levels in urine specimens containing CMV. Urinary beta 2m levels have previously been reported to be elevated in patients with CMV infection--however, when virion bound beta 2m was removed by ultracentrifugation of urine specimens, the levels of free beta 2m were not found to be elevated in these patients. Since CMV is frequently excreted by transplant recipients and acquired immunodeficiency syndrome patients, our data suggest that measurements of urinary beta 2m levels in such patients are unreliable unless the urine specimens are confirmed to be free of CMV before analysis.