Inflammation and immunity
IgM
The amount of IgM antibodies, the type the body makes first in a new infection.
Everything about this testWhat it measures
Immunoglobulins are antibodies that white blood cells make against bacteria, viruses and other invaders. IgM is the type the body makes first in a new infection; after that, IgG takes over this task. The test measures the total amount of IgM in the blood and so does not say which infection you have or have had.
- A recent or ongoing infection (raised value)
- Long-lasting inflammations, autoimmune diseases and liver diseases (raised value)
- A shortage of antibodies, usually together with a low IgG or IgA
- Rarely: a condition in which one group of immune cells makes too much of one type of IgM (M-protein)
High
A slightly raised IgM often fits a recent infection, because IgM rises first. Long-lasting inflammation, autoimmune diseases and liver diseases can also raise the value. The raised level itself causes no symptoms; those belong to the cause. Rarely, a strongly raised value means that one group of immune cells is making too much of one type of IgM (an M-protein); the laboratory looks into this further with protein electrophoresis.
Low
A low IgM usually occurs together with a low IgG or IgA and then fits an immune disorder, in which you get more infections of the ears, sinuses or airways. In CVID, IgG and IgA are always low and IgM sometimes. Medicines that suppress the immune system and protein loss through the kidneys can also lower the value. A slightly low IgM without other abnormalities and without symptoms usually has little meaning.
If your result is abnormal
With an abnormal value, the GP usually repeats the measurement together with IgA and IgG, preferably once any infection is over. With a lasting shortage and repeated infections, you are referred to an internist (specialist in internal medicine), immunologist or pediatrician. With a strongly raised value without an explanation, protein electrophoresis usually follows.
Reliability
IgM can be measured accurately, but the value fluctuates with infections and says little on its own. According to the Dutch Society for Clinical Chemistry (NVKC), IgM is measured together with IgA and IgG in people who have frequent or repeated infections, or after a total protein that is too high has been found. A raised value can only be interpreted together with the other immunoglobulins, the symptoms and, if needed, protein electrophoresis.
Limitations
- Reference values depend on age and differ by laboratory.
- A recent infection temporarily raises IgM; a measurement shortly after an infection is therefore hard to interpret.
- Medicines that suppress the immune system can lower the value.
- The result does not say which pathogen the antibodies are directed against.
How common is this
A temporarily raised IgM due to an infection is common. A shortage of antibodies is rare: CVID, the most common inborn immune disorder, occurs in about 1 in 25,000 people. There are no Dutch figures on how often an abnormal IgM is found as an isolated finding.
Who is this useful for
Useful with frequently recurring infections, together with IgA and IgG, and if a total protein that is too high was found earlier. For people without symptoms, a single IgM measurement yields little: the value varies with past infections and a slightly abnormal result is usually harmless.
Downsides and risks
- A slightly abnormal IgM without symptoms is often temporary and, without a repeat measurement, can cause unnecessary worry.
- A normal value does not rule out an immune disorder or an infection.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results