What is IgM?
When your immune system meets a pathogen for the first time, IgM is the first antibody it makes. It is a large molecule, five antibodies joined together, that gets going within days and can grab a lot at once, but not very precisely. After a week or two IgG takes over: more targeted, smaller, and it stays in the blood for months to years as memory. IgM then fades away again. That timing is the reason IgM against one pathogen is used to say whether an infection is recent: IgM present and IgG not yet means just started. This test measures something else: all your IgM together, against anything at all. That total says how much your immune system is making, not against what. Your report shows IgM in g/L, and the range for adults is the same at every lab: 0.4 to 2.3 g/L. It is almost always measured together with IgG and IgA.
Why is IgM relevant?
Total IgM is rarely measured on its own. It belongs to the trio IgG, IgA and IgM used to see whether the immune system is complete, in people who keep getting infections, and it belongs to the question of whether an excess of antibodies is of one kind, which can point at a proliferation of antibody cells. For anyone healthy without complaints, it is a value that rarely yields anything. Where it does say something is as the first antibody. A high total IgM means the immune system has just been set to work or has been at work for a long time: a recent infection, a chronic infection, a lasting inflammation. It falls again by itself once the stimulus is gone. A strongly raised IgM that persists is the exception and calls for investigation. A low IgM is usually a variant without consequences in a healthy person. It only counts when IgG is low too, because then it is the immune system as a whole that falls short, or with immunosuppressant medicines and protein loss. What you can do for your antibodies yourself is limited and general: sleep, not smoking, exercise, and vaccinations, which build exactly the memory IgG then holds on to.
IgM reference ranges
What counts beside the number:
- IgG and IgA, the other two antibody classes; together they show whether the immune system is complete
- Whether it is total IgM or an IgM test against one pathogen
- An infection in the weeks before, the most common reason for a high value
- CRP, which shows whether there is inflammation now
- The liver values, with a persistently high IgM
- Medicines that suppress the immune system, and how often you have infections, with a low value
For adults the labs use the same range, so there is little to doubt here; there is no national normal value. One lab does not run total IgM and publishes only IgM tests against individual pathogens, which have their own numbers. Read total IgM beside IgG and IgA.
What Dutch labs actually use
Three labs publish a reference value for IgM. Unilabs does not carry the determination, so this page sets three tables side by side instead of four. From 19 yrs Star-shl, Certe and Clinical Diagnostics all call 0.4 to 2.3 g/L normal, the same figure at both ends. As with IgG, there is therefore no difference between the labs for an adult to read. Certe does split its table by sex where the other two do not, but above nineteen that changes nothing: a man and a woman are given the same figures. The difference sits in the youth band only, 0.45 to 1.78 g/L for a woman and 0.36 to 1.44 for a man from one to nineteen yrs.
0.4 – 2.3g/L
Outside this range every lab calls it abnormal.
every lab calls 0.4 – 2.3 g/L normal. Outside that range every lab calls it abnormal.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Star-shl2026 | Adults | 0.4–2.3 g/L |
| Certe2026 | Women 1 to 19 yrs | 0.45–1.78 g/L |
| Men 1 to 19 yrs | 0.36–1.44 g/L | |
| Women from 19 yrs | 0.4–2.3 g/L | |
| Men from 19 yrs | 0.4–2.3 g/L | |
| Clinical Diagnostics2026 | Adults | 0.4–2.3 g/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
IgM high or low: what it means
A high IgM comes, in order of how often it occurs, from: a recent infection, which has just set the immune system to work; a lasting infection or inflammation, from hepatitis to a chronic bowel inflammation; an autoimmune disease; rarely an autoimmune liver disease that keeps IgM high; and rarely a proliferation of the cells that make IgM. The higher and the more lasting, the more the last two come into view. A slightly raised IgM after a past infection is the most common outcome and falls within weeks. A low IgM usually means nothing in a healthy person; a small share of people naturally make little IgM without being troubled by it. It counts when IgG and IgA are low too, with medicines that suppress the immune system, and with protein loss through kidneys or gut. Very rarely it is an inborn deficiency with recurring infections. What you do about it: a high IgM from an infection needs time, not treatment. A low IgM without infections needs nothing. If IgM stays strongly raised or all three classes are low, that is a question for further investigation, and that belongs with a doctor. IgM belongs beside IgG and IgA. With a high value CRP belongs beside it, which shows whether there is inflammation now, and the liver values. And check that it is total IgM: an IgM test against one pathogen carries the same name and has its own numbers.
What lowers it
Usually a variant without consequences; counts when the other classes are low too.
| Cause | How often |
|---|---|
| Medicines that suppress the immune systemPrednisone, methotrexate, rituximab and other immunosuppressants lower antibody production, usually together with IgG | Sometimes |
| Protein loss through kidneys or gutWith a leaking kidney filter or a gut that loses protein, antibodies are lost with it; IgM as a large molecule sometimes least | Rare |
| An inborn IgM deficiencyRare; some people naturally make little IgM without complaints, a small share with recurring infections | Rare |
What raises it
The immune system just set to work, or at work for a long time.
| Cause | How often |
|---|---|
| A recent infectionIgM gets going within days and fades again after weeks as IgG takes over; a slightly raised IgM after an infection is the most common outcome | Often |
| Lasting inflammation or infectionA chronic infection such as hepatitis or a lasting inflammation keeps IgM production going | Sometimes |
| Autoimmune diseasesRheumatoid arthritis, lupus and other autoimmune diseases raise IgM along with the inflammation | Sometimes |
| An autoimmune liver diseaseIn primary biliary cholangitis, an autoimmune disease of the bile ducts, a high IgM is characteristic | Rare |
| A proliferation of antibody cellsRare: a strongly raised IgM of one kind fits Waldenström's disease, and then further investigation is needed | Rare |
How does an IgM blood test work?
- Referral
- Not needed. Ask for total IgM, because an IgM test against one pathogen carries the same name and has its own numbers.
- Fasting
- Not needed.
- The result
- A single number in g/L, with the same range for adults at every lab. Usually available within a few days.
- Repeating
- A slightly raised IgM after an infection again after a few months; it should have fallen by then. A persistently strongly raised IgM is investigated further.
- Where to draw
- You can draw at 250+ locations near you, no referral needed. See the locations
Frequently asked questions
What is IgM?
Immunoglobulin M is the first antibody your immune system makes with a new pathogen: a large molecule that gets going within days and can grab a lot at once, but not very precisely. After a week or two IgG takes over and IgM fades again. This test adds up all your IgM together, against anything at all.
What is a normal IgM level?
From age 19, 0.4 to 2.3 g/L, the same at every lab and equal for men and women. In childhood the range sits lower.
What does a high IgM mean?
Usually that your immune system has just been set to work or has been at work for a long time: a recent infection, a chronic infection such as hepatitis, a lasting inflammation or an autoimmune disease. A slightly raised IgM after an infection is the most common outcome and falls within weeks. A strongly raised IgM that persists is the exception and fits an autoimmune liver disease or a proliferation of antibody cells; then further investigation is needed.
What does a low IgM mean?
In a healthy person usually nothing; a small share of people naturally make little IgM without being troubled by it. It counts when IgG and IgA are low too, because then the immune system as a whole falls short, with medicines that suppress the immune system, and with protein loss through kidneys or gut. An inborn deficiency with recurring infections is rare.
What is the difference between total IgM and an IgM test against a pathogen?
The total adds up all your IgM and says how much your immune system is making. An IgM test against one pathogen, for instance the virus of glandular fever, says whether you have had that infection recently: IgM present and IgG not yet means just started. They carry the same name and have different numbers, so check which of the two is on your report.
Can I raise or lower my IgM?
Not deliberately, and there is no need to. A high IgM from an infection falls by itself; a low IgM without infections needs nothing. What does your immune system good in general is sleep, not smoking, exercise and vaccinations, which build exactly the memory IgG then holds on to.
Which tests include IgM?
IgM is part of Advanced, the broader panel. It is not orderable yet.
Related biomarkers
Sources
- 1.Star-shl, test catalogue (Dutch): immunoglobulin IgA, IgG, IgM. 2026. star-shl.nl
- 2.Certe, test catalogue (Dutch): total IgM. 2026. bepalingenwijzer.certe.nl
- 3.Clinical Diagnostics, lab guide (Dutch): IgM. 2026. clinicaldiagnostics.nl
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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IgM is part of Advanced, the broader panel. It is not orderable yet.
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