An IgG titer test measures the level of specific IgG antibodies in a blood sample to determine past exposure or immunity to a pathogen (or response to vaccination). Results are reported as a titer or concentration and interpreted against lab-specific reference ranges. It helps confirm prior infection, assess vaccine response, or guide revaccination; timing and test type affect accuracy and clinical interpretation.

A normal total serum IgG level in adults is roughly 7–16 g/L (700–1600 mg/dL). Reference ranges vary by laboratory and age: infants and young children have lower IgG, and elderly values may differ. Clinical interpretation should use the lab’s specific reference interval and be correlated with symptoms and specialist input when results are abnormal.

An IgG antibody positive result means your immune system has produced IgG-class antibodies to a specific pathogen (from past infection or vaccination). It indicates prior exposure and likely some level of immune memory, often developing weeks after infection and persisting for months. It does not prove current active infection nor guarantee complete or long-lasting immunity; interpretation should consider timing, symptoms, and clinical context.

IgM and IgG titers measure different antibody responses. IgM rises first during acute or recent infection, peaks early, then falls, so a positive IgM suggests recent exposure. IgG appears later, indicates past infection or established immunity and usually persists long-term as memory. Comparing their levels (rising or falling) helps determine timing of infection and vaccine response.

High IgG levels do not automatically mean an active infection. IgG rises after exposure and usually indicates past or ongoing immune response, long-term immunity, or chronic inflammation. Elevated total IgG can result from chronic infections, autoimmune disease, liver disease, or gammopathies. To identify an active infection, clinicians use specific antibody tests, IgM, antigen tests or PCR plus symptoms and history.

A "normal" antibody titer means antibody levels are in the range considered protective for a specific infection or vaccine; there is no single universal normal. Labs report titers as positive/negative or numeric units, and protective cutoffs differ by disease (for example, hepatitis B surface antibody ≥10 mIU/mL is usually considered protective). Interpretation depends on the test, lab reference range and clinical context.