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Blood Test Tracker

Immunoglobulin M (IgM)

The first antibody your body makes against a new germ. Reported in mg/dL in the US and in g/L in many other countries.

AI-verified against cited sources. Awaiting expert reviewAlso called IgMLOINC 2472-9

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What it is

IgM is the first antibody your body makes when it meets a new germ. It is a large antibody that stays mostly in the bloodstream and gives short-term protection while longer-lasting antibodies, such as IgG, are being made. This test measures the total IgM in your blood, not IgM against a specific germ.

Why it matters

Total IgM helps your care team look at how your antibody system is working. IgM can be higher with some infections and with liver and autoimmune conditions. A high level can also come from one clone of cells making a single IgM antibody, which is why a high result is often followed by protein electrophoresis. A low level can go with some immune conditions or with medicines that suppress the immune system.

If it’s low

A low IgM means your blood holds less of this antibody than is usual. Some people have a low level with no symptoms. Others have it as part of a wider drop in antibodies, or because of a medicine or a blood condition. Many other things can cause this, and your clinician can put it in context.

Common causes

  • A result just under the lower limit, which happens in a small share of healthy people because ranges are set that way
  • Selective IgM deficiency or a primary antibody deficiency such as common variable immunodeficiency (uncommon)
  • Medicines that suppress the immune system, including rituximab, steroids and chemotherapy
  • Blood cancers such as chronic lymphocytic leukemia or multiple myeloma
  • Protein loss through the kidneys or the gut, or severe burns

What can help

  • Ask whether any of your medicines could be lowering it
  • Ask whether IgG and IgA were normal and whether you should recheck this later

If it’s high

A high IgM most often reflects a broad rise from many antibody-making cells, for example during or after an infection or with a liver or autoimmune condition. Less often it comes from one clone of cells making a single IgM antibody. Many other things can cause this, and your clinician can put it in context.

Common causes

  • Recent or ongoing infections
  • Liver conditions, including hepatitis and cirrhosis
  • Autoimmune and connective tissue conditions
  • A monoclonal gammopathy, such as IgM MGUS or Waldenström macroglobulinemia
  • Amyloidosis (uncommon)

What can help

  • Ask whether protein electrophoresis would help tell a broad rise from a single-antibody (monoclonal) rise
  • Ask whether a recent infection or a liver or autoimmune condition could explain it

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on sex and age. Choose women or men to see the one that applies.

Children and teens 12 ranges

See IgM by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Age: IgM rises through infancy and childhood (Mayo)
  • Sex: Labcorp prints higher intervals for females than males, while Mayo and ARUP print one interval for all adults
  • Recent infection can raise IgM for a time
  • Medicines that suppress the immune system, such as rituximab, steroids and chemotherapy, can lower it
  • Method: nephelometry and turbidimetry assays from different manufacturers are not always comparable
  • Very cloudy (lipemic) samples can't be measured reliably. Mayo rejects grossly lipemic specimens, and ARUP lists grossly hemolyzed and lipemic specimens as unacceptable.
  • Results from different manufacturers' methods may not be comparable, so compare your results using the same lab and method when you can (Mayo).
  • Cold-reacting proteins (cryoglobulins or cold agglutinins) can distort the IgM measurement (Waldenström 2013 review).
  • Medicines that suppress the immune system, such as rituximab and steroids, can lower IgM. Tell your clinician about everything you take, and don't stop a medicine without asking.

IgM changes over weeks to months. A recent infection can raise it temporarily.

When to talk to a clinician

Talk with your clinician about a high or low result, especially if your report mentions a monoclonal protein. Let them know sooner about vision changes, new headaches, nosebleeds or bleeding gums, numbness or tingling in your hands or feet, drenching night sweats, unexplained weight loss, or repeated infections.

Questions you could ask

  • How does my IgM fit with my IgG, IgA and the rest of my protein tests?
  • Is my IgM rise broad or from a single antibody, and would protein electrophoresis help?
  • Could a recent infection, a liver condition or an autoimmune condition explain it?
  • Could one of my medicines or another condition be lowering my IgM?
  • Were my IgG and IgA normal, and should we recheck this in a few months?

Questions people ask

Does a high IgM mean I have Waldenström macroglobulinemia?

Usually not. A mildly high IgM is more often caused by an infection, a liver condition or an autoimmune condition. If your IgM is well above the range, your clinician may order protein electrophoresis to see whether one antibody is responsible.

Why does my lab's range differ from the one shown here?

Labs use different instruments and set ranges from different groups of healthy people, and some split by sex. For adults the range runs from about 20 to 45 mg/dL at the low end and 150 to 286 mg/dL at the high end across Labcorp, ARUP, Mayo and ABIM. Use the range printed on your own report first.

How do I convert g/L to mg/dL?

Multiply g/L by 100. For example, 1.5 g/L is 150 mg/dL. To go the other way, divide mg/dL by 100.

Show the science and sources

Units

  • 1 mg/dL = 1 mg/dL
  • 1 mg/dL = 0.01 g/L
  • 1 mg/dL = 10 mg/L

Open the IgM unit converter

Is a change real?

IgM naturally varies about 3.9% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 12% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: The European Biological Variation Study (EuBIVAS): a summary report.

For clinicians and researchers

IgM is the first isotype made in a primary immune response (Mayo, MedlinePlus) and circulates mostly as a large pentamer. About 5% of the immunoglobulin in the gamma zone on serum protein electrophoresis is IgM (Mayo). It is measured by nephelometry (Mayo) or immunoturbidimetry (ARUP), and nephelometric quantitation may be unreliable in lipemic serum (Mayo). Adult intervals differ widely: lower limits run from 20 to 45 mg/dL and upper limits from 150 to 286 mg/dL across Labcorp, ARUP, Mayo and ABIM, and Labcorp splits by sex (males 20–172, females 26–217 mg/dL). Elevated IgM can be polyclonal (hepatic disease, connective tissue disease, infection) or monoclonal (macroglobulinemia, primary systemic amyloidosis, MGUS), and electrophoresis and immunofixation separate the two (Mayo). Waldenström macroglobulinemia is by definition accompanied by a monoclonal IgM, which in most cases lies within 15–45 g/L. Nephelometric IgM runs systematically higher than the M-protein measured by densitometry, so follow-up should use the same method and ideally the same laboratory, and cryoglobulins or cold agglutinins can distort the IgM result (Waldenström 2013 review). Low IgM occurs in primary and secondary antibody deficiency (Ameratunga 2014; Compagno 2014).

LOINC 2472-9 (primary). Specimen: serum-or-plasma.

Sources

  1. Immunoglobulin M (IgM), Serum (test ID IGM), Mayo Clinic Laboratories
  2. Immunoglobulins (IgA, IgG, IgM), Quantitative (test 0050630), ARUP Laboratories
  3. Pediatric Testing Reference Ranges (includes adult intervals for Labcorp tests 001776, 001784, 001792 and 001834), Labcorp Diagnostics
  4. ABIM Laboratory Test Reference Ranges, January 2026, American Board of Internal Medicine (2026)
  5. Immunoglobulins Blood Test, MedlinePlus (National Library of Medicine) (2025)
  6. Comparison of Diagnostic Criteria for Common Variable Immunodeficiency Disorder, Frontiers in Immunology (2014)
  7. Immunoglobulin Replacement Therapy in Secondary Hypogammaglobulinemia, Frontiers in Immunology (2014)
  8. How to manage Waldenstrom's macroglobulinemia, Leukemia (2013)
  9. LOINC code lookup (NLM Clinical Tables), National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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