Explanation

Aspergillus fumigatus IgG: what is measured?

Aspergillus fumigatus is a mold found everywhere in the environment, in compost, soil, hay and damp rooms. Almost everyone regularly breathes in spores without becoming ill. In some people with asthma or cystic fibrosis, the immune system reacts strongly to it, and in people with a damaged lung or a weakened immune system, the mold can settle in the lung. This test measures IgG antibodies against the mold, a sign that the immune system has been exposed to it for a longer time.

What can it detect?

Support in investigating allergic bronchopulmonary aspergillosis (a strong immune reaction to the mold in the lungs) in asthma or cystic fibrosis
Support in investigating a long-lasting mold infection in a damaged lung, for example in a cavity after tuberculosis

Result

What does the result mean?

Positive result

A positive result means that your immune system has made antibodies against this mold. This is common without disease: in cystic fibrosis, about 70 in 100 people have antibodies against Aspergillus, while only a small proportion of them develop symptoms. In the guideline, a raised Aspergillus IgG therefore only counts as a supporting criterion, alongside required criteria such as a raised Aspergillus-specific IgE and a strongly raised total IgE. Without lung symptoms, a positive result says little.

Negative result

A negative result makes a long-lasting mold infection or a strong immune reaction to Aspergillus less likely, but does not rule it out. People with a weakened immune system, precisely the group with the highest risk of an invasive infection, often make few antibodies; in them, an antibody test therefore says little and the antigen test (galactomannan) says more.

After an abnormal result

With a positive result and matching lung symptoms, the doctor usually also has total IgE and Aspergillus-specific IgE measured and imaging of the lungs done; assessment and any treatment go through the pulmonologist. An abnormal result on its own is not a reason to treat: there must also be symptoms. Aspergillosis is not notifiable in the Netherlands.

Reliability

How reliable is the test?

In people without lung symptoms, the meaning of a positive result has been little studied. The quality standard for cystic fibrosis lists Aspergillus IgG as a supporting criterion for diagnosing allergic bronchopulmonary aspergillosis, alongside required criteria; the standard notes that about 70 in 100 people with cystic fibrosis have such antibodies, while only a small proportion develop symptoms. Because almost everyone breathes in spores of this mold every day, a positive result on its own is not a sign of disease. This test is not suitable for an invasive mold infection.

What can affect the result?

Exposure to the mold is normal; antibodies also occur in people without symptoms.
In people with a weakened immune system, the test can be negative even though there is an infection.
The test is not suitable for detecting invasive aspergillosis; for that, the antigen test, among others, says more.
Laboratories use different tests and cut-off values; results cannot simply be compared with each other.

Who it is for

Who is the test useful for?

Useful for

Can be useful in asthma or cystic fibrosis with increasing shortness of breath, coughing up mucus and recurring flare-ups, as part of investigating a strong immune reaction to the mold, and when a long-lasting mold infection in a damaged lung is suspected. Not useful as a general check in people without lung symptoms: antibodies occur in healthy people and a positive result does not change the approach.

How common is it?

Aspergillus fumigatus is found everywhere in the environment and almost everyone regularly breathes in spores without becoming ill. Of people with persistent asthma, an estimated 20 to 25 in 100 are sensitive to one or more types of mold; only a small proportion of them develop the strong immune reaction in the lungs called allergic bronchopulmonary aspergillosis. In people with cystic fibrosis, about 70 in 100 have antibodies against Aspergillus, without most of them having symptoms from it.

FMS Richtlijnendatabase (Cystic Fibrosis quality standard and Severe Asthma guideline)

Drawbacks and risks

Antibodies against this mold are common without disease; a positive result can cause unnecessary worry and unnecessary further testing.
Treatment with antifungal medicines has many side effects and interactions with other medicines; starting it based on a result alone is undesirable.

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