Inflammation and immunity
IgG
The amount of IgG antibodies, the main antibodies in the blood; low in some immune disorders.
Everything about this testWhat it measures
Immunoglobulins are antibodies that white blood cells (B cells) make against bacteria, viruses and other invaders. IgG is the type present in the largest amount in the blood, which the body mainly makes on a second contact with a pathogen or after a vaccination; it provides longer-lasting protection. During pregnancy, IgG passes through the placenta to the child and protects the baby in the first months. The test measures the total amount of IgG, not the defense against one specific pathogen.
- A shortage of antibodies, for example in CVID (common variable immunodeficiency)
- A shortage due to medicines that suppress the immune system or due to protein loss through the kidneys
- Long-lasting infections, inflammations, autoimmune diseases and liver diseases (raised value)
- Rarely: a condition in which one group of immune cells makes too much of one type of IgG (M-protein)
High
A slightly raised IgG is common during or after an infection. Long-lasting inflammation, autoimmune diseases such as rheumatism and liver diseases also give a higher 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 IgG (an M-protein); with protein electrophoresis the laboratory can distinguish this from a general increase.
Low
A low IgG means there are fewer antibodies, which makes you more prone to infections of the ears, sinuses and airways. A known cause in adulthood is CVID, an immune disorder in which the production of antibodies falls short; it sometimes only causes symptoms around the age of twenty or thirty. Other causes are medicines that suppress the immune system and protein loss through the kidneys, for example in kidney disease. If all types of immunoglobulins are low, you are extra vulnerable to infections. Rarely, a low value is due to a bone marrow disease that crowds out the production of healthy white blood cells.
If your result is abnormal
With a low value, the GP usually repeats the measurement together with IgA and IgM. With repeated infections or a clear shortage, you are referred to an internist (specialist in internal medicine), immunologist or pediatrician, who looks at the response to vaccinations, among other things. With a strongly raised value without a clear cause, protein electrophoresis usually follows.
Reliability
IgG can be measured accurately, but a single value says only a limited amount about how well the immune system works. According to the Dutch Society for Clinical Chemistry (NVKC), the test is mainly done with frequently recurring infections, together with IgA and IgM, or after a total protein that is too high has been found. A normal amount of IgG makes an antibody shortage unlikely as the explanation for many infections. Whether the immune system really falls short is assessed by a specialist with additional tests, including the response to vaccinations.
Limitations
- Reference values depend on age and differ by laboratory.
- A recent infection or inflammation can temporarily raise the value.
- Medicines that suppress the immune system can lower IgG.
- After treatment with antibodies given by drip, the test does not measure your own production.
How common is this
An inborn shortage of antibodies is rare: CVID occurs in about 1 in 25,000 people and is still the most common inborn immune disorder. A raised IgG due to an infection, inflammation or liver disease is much more common. There are no Dutch figures on how often an abnormal IgG is found as an isolated finding.
Who is this useful for
Useful with frequently recurring or severe infections, such as repeated pneumonia, sinus or ear infections, with infections that respond poorly to antibiotics, and for monitoring during medicines that suppress the immune system. Also useful if a total protein that is too high was found earlier. In people without such symptoms, a single IgG measurement yields little.
Downsides and risks
- A slightly abnormal value without symptoms can cause unnecessary worry and further testing.
- A normal value does not completely rule out an immune disorder, because the defense against specific pathogens can still fall short.
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