What are the diagnostic criteria for cytomegalovirus (CMV) seropositivity: IgM, IgG, PCR, or leukocytic viral DNA?
Adel Al-Ansary, MD
Classically, detection of IgG antibodies to CMV is diagnostic of past infection and synonymous with the term "seropositivity". Transplant physicians have used this term to predict risk for the development of posttransplant CMV disease. Without appropriate prophylactic measures, the seronegative recipient of an organ from a seropositive donor is at the highest risk (> 60%) of developing CMV disease.
Donors generally have intact humoral responses, and so IgG detection is appropriate for diagnosis of donor seropositivity. In such individuals, there are many acceptable methods for detecting anti-CMV IgG. However, potential transplant recipients may be immunosuppressed at inquiry, and as such, should have a more sensitive assay for detection of IgG antibody. Drs. Clewley, Emery, and Griffiths at the Royal Free Hampstead Hospital in London, United Kingdom, promote the use of an enzyme-linked immunoassay for detection of anti-CMV in the immunocompromised patient.
Nevertheless, there should be a distinction between "seropositivity," which indicates past infection, and "serum-positivity" by any number of assays for antigen or DNA from actively replicating virus. Detection of the early matrix protein pp65, as occurs with a positive CMV "rapid antigen" test or detection of CMV DNA by means of polymerase chain reaction (PCR) from peripheral blood leukocytes or bodily fluid or biopsy material, is an indication of actively replicating virus. This state is distinct from latent infection and is traditionally termed CMV "disease." Again, because transplant patients have variable humoral responses and the rapid antigen or PCR tests are more sensitive, there is no indication for assessing the presence of IgM.
To shorten a lengthy story, the term "seropositivity" is slang for the presence of anti-CMV IgG and indicates past infection by the virus.