Immunoglobulin M (IgM) in Serum or Plasma by Immunoassay

What Does IgM Measure?

IgM is produced primarily by plasma cells in response to infections, vaccines, or chronic conditions. It’s particularly useful for detecting recent infections because it appears shortly after exposure and can linger longer than other antibodies like IgG. This test helps doctors track immune responses and diagnose conditions such as viral infections, autoimmune diseases, or certain cancers.

Why Might You Need This Test?

Your healthcare provider may order an IgM test to diagnose or monitor conditions like viral hepatitis, measles, rubella, Lyme disease, or other infections. It can also help assess immune function in people with chronic illnesses or after receiving vaccines. Sometimes, IgM levels are checked alongside other antibody tests to get a clearer picture of your immune response.

Common Uses in Healthcare

IgM testing is often used in conjunction with other blood tests to confirm diagnoses, evaluate treatment progress, or investigate unexplained symptoms. For example, high IgM levels might suggest an active infection, while abnormal levels could indicate an underlying immune disorder.

What to Expect Before the Test

No special preparation is usually needed for this test. You may have a small needle inserted into your arm or vein to draw a blood sample. If you’re taking blood from your finger (for fingerstick tests), you might need to fast or avoid certain medications. Always follow your healthcare provider’s instructions.