IgM titer is the measured level of immunoglobulin M (IgM) antibodies in the blood. IgM appears early after infection or recent vaccination, so a high or rising IgM titer suggests recent or acute exposure. Low or absent IgM implies past infection or no recent response. Results require clinical correlation and sometimes paired IgG testing to confirm timing and immunity.

A positive IgM indicates a recent or acute infection by the tested pathogen, reflecting an early immune response. It suggests recent exposure or ongoing infection but can produce false positives from cross‑reactivity. Confirmation with clinical assessment, repeat IgM/IgG testing, or molecular tests (PCR) is often needed to determine timing and treatment. Discuss results with your healthcare provider for appropriate management.

The IgM antibody test is done to detect recent or current infections because IgM is the first antibody the body makes after exposure. It helps diagnose acute infections (e.g., viral or bacterial), distinguish recent versus past infection when paired with IgG, guide treatment and infection-control decisions, and monitor early immune response. Results need clinical correlation since false positives or negatives can occur.

IgM and IgG serve different roles. IgM appears early and suggests recent/acute infection; IgG develops later and indicates past exposure or longer-term immunity. Neither is universally “better”—use IgM to detect recent infection (PCR is often best early), and IgG to assess prior exposure or immune response. Combined testing and correct timing improve accuracy; antibody tests can still give false results.

IgM positive for Salmonella typhi suggests recent or acute infection and raises suspicion of early typhoid fever, but it is not definitive alone. Serologic IgM can give false positives or cross‑react with other infections; clinical findings and confirmatory tests (blood culture or PCR) are needed. Repeat testing, rising IgG, or culture confirmation helps establish a true diagnosis and guide treatment.

IgM is linked to acute and recent infections (e.g., viral hepatitis, EBV, CMV, rubella) as the early antibody response. Elevated or monoclonal IgM occurs in Waldenström macroglobulinaemia and some MGUS. IgM autoantibodies contribute to rheumatoid arthritis, cold agglutinin disease and cryoglobulinaemia. Low or defective IgM is seen in hyper-IgM syndromes (primary immunodeficiency).