Immunoglobulin M (IgM) in Serum or Plasma

What Does IgM Measure?

IgM is one of the key proteins in your immune system that helps your body fight off infections. It appears early in the immune response and can indicate whether your body is currently dealing with an active infection or responding to a past one. Unlike other antibodies like IgG, IgM is typically produced in larger quantities during the initial phase of an infection.

Why Might Your Doctor Order This Test?

Your doctor may order an IgM test to diagnose or monitor conditions such as infections (like viral hepatitis, Lyme disease, or certain bacterial infections), autoimmune diseases, or to check for immune system responses after vaccination. It can also help determine if you have an ongoing immune reaction or if a previous infection is still affecting your body.

When Is an IgM Test Used?

IgM tests are often used in the early stages of diagnosing infections, especially when other tests may not yet show results. For example, it can help confirm a recent exposure to certain viruses or bacteria. Doctors may also use it to track how your body is responding to treatment for an infection or disease.

What Could High or Low IgM Levels Indicate?

Elevated IgM levels may suggest an active infection, a chronic immune condition, or an autoimmune response. Low IgM levels might indicate a weakened immune system, certain genetic disorders, or conditions affecting antibody production.