VCAIgG

VCAIgG refers to immunoglobulin G antibodies directed against the viral capsid antigen of the Epstein-Barr virus (EBV). It is a commonly used serologic marker to assess prior EBV exposure and, when interpreted with other EBV antibodies, to infer the stage of infection. VCA IgG antibodies typically appear early in infection and persist for life, helping distinguish past infection from false-positive or acute-phase results. In contrast, VCA IgM against the same antigen is usually present during acute infection, while EBNA (EBV nuclear antigen) IgG appears later and also persists for life.

Testing for VCAIgG is usually performed by enzyme-linked immunosorbent assay (ELISA), chemiluminescent immunoassay, or immunofluorescent methods. Results are reported as positive or negative, often with a quantitative index value or titer. In clinical practice, VCA IgG is interpreted together with VCA IgM and EBNA IgG to determine whether an EBV infection is acute, recent, past, or unlikely. A typical pattern is: in acute primary infection, VCA IgM is positive, VCA IgG is positive, and EBNA IgG is negative or not yet detectable; in past infection, VCA IgG is positive, EBNA IgG is positive, and VCA IgM is negative.

Clinical utility of VCAIgG includes evaluation of suspected infectious mononucleosis, assessment of EBV exposure in patients with compatible symptoms, and pre-transplant or other immunocompromised settings where EBV immunity status is relevant. Limitations include potential false positives or negatives, assay variability, and the fact that serologic patterns can vary during the course of infection or in immunocompromised individuals. Therefore, VCAIgG results are best interpreted within the context of the complete EBV serology panel and the clinical picture.