IgM
What this test measures
IgM is the large, first-response antibody the immune system makes in the first days of a new infection, before switching to IgG. The blood test measures the total amount of IgM of all specificities, not antibody to any one germ. It is usually reported together with IgG and IgA.
Why doctors request it
Doctors request it with IgG and IgA when looking at recurrent infections, unexplained high blood protein and myeloma and related conditions, particularly one called Waldenstrom's macroglobulinaemia, which makes IgM.
What commonly pushes it up
- A recent or current infection, particularly viral
- Waldenstrom's macroglobulinaemia and some other blood conditions
- Liver disease, particularly primary biliary cholangitis
- Some autoimmune conditions
- Some inherited immune conditions where the switch from IgM to IgG fails
What commonly pushes it down
- Immune-suppressing medicines, including rituximab and chemotherapy
- Myeloma of another type, which crowds out normal antibody production
- Protein loss through the kidneys or the gut
- Inherited and acquired immune deficiencies
- Older age, a little, in the general population
Everyday reasons for a value outside the range
- A recent infection or vaccination raises it for a few weeks
- It is a little higher in women
- Methods differ between laboratories
About the sample
No fasting needed. Read alongside IgG, IgA and serum protein electrophoresis from the same sample.
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Read my report freeThis is an educational summary of results you uploaded. It is not medical advice, a diagnosis or a treatment plan, and it does not replace the doctor who requested the test. If you are worried, or a result is marked outside range, discuss it with your doctor. Written and reviewed by a UK consultant physician. Reference ranges vary between laboratories.