CMV tests: antibodies and PCR
Explanation
Cytomegalovirus (CMV) is a common virus that can remain in the body after an infection. CMV tests either look for antibodies, proteins made by the immune system, or detect genetic material from the virus. These tests answer different questions.
What do IgG and IgM mean?
In adults and children over 12 months, positive CMV IgG usually shows that infection occurred at some point. It does not tell you when. Positive IgM alone cannot establish a first, recent infection because IgM can also occur when infection becomes active again.
Depending on the question, a clinician may compare samples or use additional tests. A result labelled positive is not, by itself, proof that CMV is causing current symptoms.
How is PCR different?
PCR looks for the virus's genetic material in the sample. The meaning depends on the sample and the reason for testing, including pregnancy or a weakened immune system.
What about newborns?
Antibody tests cannot diagnose infection acquired before birth. This usually requires saliva PCR, confirmed with urine testing, within the first three weeks of life. Testing later cannot reliably distinguish infection before birth from infection acquired afterward.
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