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Immunoglobulin M (IgM)

Published: July 27, 2026Updated: August 25, 2026

Immunoglobulin M (IgM) is a type of antibody produced by the immune system in response to infections. It is often the first antibody to appear in the early stages of an immune response.

Quick summary

IgM is a primary antibody in acute immune responses, typically the first to respond to new infections.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
mg/dL
Clinical utility
diagnostic
Result kind
quantitative
FDA-cleared
Roche IgM, Abbott IgM, Siemens IgM, Beckman IgM
interpretation: {"text":"May indicate an acute infection, autoimmune disorder, or chronic inflammatory condition.","label":"Elevated IgM (>230 mg/dL)"}; {"text":"Could suggest an immune deficiency, lymphoma, or other lymphoproliferative disorders.","label":"Decreased IgM (<40 mg/dL)"}

Immunoglobulin M (IgM) is the largest antibody in the human circulatory system and is essential for the initial immune response to new infections. It is primarily produced by B cells and is highly effective at binding to pathogens, aiding in their neutralization and destruction.

The normal range for IgM levels in the blood is typically between 40–230 mg/dL. Elevated levels may indicate an acute infection, autoimmune disorder, or other inflammatory conditions, while decreased levels can suggest certain immune deficiencies or lymphoproliferative disorders.

IgM testing is often used diagnostically to detect recent infections or to monitor the status of the immune system. It is commonly employed in conjunction with other tests to provide a comprehensive assessment of immune function.

Frequently asked questions

What does a high IgM level mean?
A high IgM level may indicate an acute infection, an autoimmune disorder, or a chronic inflammatory condition.
What does a low IgM level mean?
A low IgM level may suggest an immune deficiency, lymphoma, or other lymphoproliferative disorders.
  1. 1
    Immunoglobulin M (IgM)Source
  2. 2
    IgM: The First ResponderSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy