Immunoglobulin M (IgM) Subclass Measurement (Serum)

Why This Test Is Done

Doctors may order IgM subclass testing to diagnose or monitor conditions such as infections (e.g., hepatitis, mononucleosis), autoimmune diseases, or certain cancers. It can also help assess immune function or response to treatments.

No special preparation is usually needed, but you may be asked to fast for 8–12 hours if your blood is drawn early in the morning for more accurate results.

During the test, a healthcare provider will draw blood from a vein in your arm. You may feel a slight pinch, but it typically doesn’t cause significant discomfort.

Results may show elevated IgM levels in response to infections, immune disorders, or chronic conditions. Low levels could indicate immune deficiencies or certain genetic disorders.

Your doctor will compare your results with your medical history and other tests to determine the next steps, such as further evaluation or treatment adjustments.

IgM levels are often checked in cases of suspected infections (e.g., viral hepatitis, Lyme disease), autoimmune diseases (e.g., lupus), or conditions like multiple myeloma.

Elevated IgM can signal recent or ongoing infections, while persistently high levels may require further investigation to rule out underlying immune or inflammatory conditions.