Immunohistochemistry (IHC) for CMV uses antibodies to detect cytomegalovirus proteins in tissue sections, identifying infected cells by characteristic nuclear and cytoplasmic staining. It’s performed on biopsy specimens to confirm CMV disease, distinguish active infection from latent virus, and guide treatment. IHC is rapid, specific, and commonly used alongside PCR and routine histology for accurate diagnosis.

Confirmatory testing for CMV is nucleic acid testing (PCR) to detect CMV DNA—quantitative PCR on blood confirms active infection and is used for viral‑load monitoring. For congenital CMV, PCR on saliva or urine collected within the first 2–3 weeks of life confirms the diagnosis. Serology (IgM or IgG seroconversion) can support recent infection but is less specific than PCR.

The most accurate test for CMV is quantitative CMV PCR (nucleic acid testing) to detect and measure viral DNA in blood, plasma, urine, or saliva, which confirms active infection and guides treatment. For congenital CMV, PCR on urine or saliva collected within the first three weeks of life is diagnostic. Serology (IgG/IgM and IgG avidity) helps assess past exposure and timing but is less definitive for active disease.

The gold standard for diagnosing CMV colitis is colonoscopy with mucosal biopsy demonstrating characteristic CMV cytopathic changes (large cells with intranuclear and intracytoplasmic inclusions), confirmed by immunohistochemistry or tissue PCR. Endoscopic biopsy provides histopathologic confirmation and viral detection, which guide antiviral therapy and distinguish CMV from other causes of colitis.

Positive immunohistochemistry means the tested antibody detected its target antigen in the tissue, shown by specific staining (nuclear, cytoplasmic or membrane). It indicates the presence of particular proteins that help identify cell type, tumour origin, prognosis, or therapy targets. Interpretation requires correlation with microscopic appearance, controls and clinical context, because expression can be seen in normal or non‑neoplastic cells as well as in disease.

If you test positive for CMV, discuss results with your doctor to determine whether it is a past (latent) or recent infection. Pregnant women need urgent obstetric evaluation—additional blood tests, ultrasound and possibly amniocentesis—to assess fetal risk. Immunocompromised people may need antiviral treatment and viral-load monitoring. Newborns require PCR testing and hearing assessment. Practice strict hand hygiene and follow up with specialists.