Immunoglobulin M (IgM) in Whole Blood

What Does IgM Measure?

IgM is a type of antibody produced primarily by plasma cells in the liver and spleen. It plays a key role in the early immune response to infections, helping your body fight off pathogens like bacteria and viruses. IgM levels can rise shortly after exposure to an antigen (a substance that triggers an immune response) and remain elevated for a longer period compared to other antibodies like IgG.

Why Might Your Doctor Order This Test?

Your doctor may order an IgM blood test to diagnose or monitor conditions such as infections (e.g., hepatitis, certain viral infections), autoimmune diseases, or to assess immune responses after vaccination. It can also help determine if an infection is active or if the body is still responding to a past exposure.

When Might IgM Levels Be Abnormal?

Elevated IgM levels may indicate an ongoing infection, chronic immune activation, or certain genetic or autoimmune conditions. Lower-than-normal IgM levels might suggest immune deficiencies or certain genetic disorders affecting antibody production.

What Does a Positive or Abnormal Result Mean?

An abnormal IgM result doesn’t always mean you have an active infection. It could indicate past exposure, chronic conditions, or other immune-related issues. Your doctor will interpret the result in the context of your symptoms, medical history, and other test results.