Explanation

Helicobacter pylori IgA: what is measured?

Helicobacter pylori is a bacterium that can live in the stomach lining and can cause long-lasting inflammation of the stomach or the first part of the small intestine. Because the bacterium lives on a mucous membrane, the immune system makes IgA antibodies in addition to IgG. This test measures IgA in the blood. Like IgG, these antibodies can remain present for a long time after the bacterium has gone; a stool test or a breath test shows whether the bacterium is there now.

What can it detect?

Contact with Helicobacter pylori, now or in the past, without distinguishing between the two

Result

What does the result mean?

Positive result

A positive result means that IgA antibodies against the stomach bacterium were found. That fits a current or previous infection, but this result cannot tell whether the bacterium is still there now. The meaning of IgA alongside IgG has been little studied, and for IgA there are no agreed cutoff values that apply to all laboratories. Whether the bacterium is present at this moment is shown by a stool test or a breath test.

Negative result

A negative result does not rule out an infection with the stomach bacterium. Not everyone with the bacterium makes detectable amounts of IgA, so this test misses infections more often than IgG. With stomach complaints, a stool test or a breath test gives a more reliable answer.

After an abnormal result

With a positive result and stomach complaints, a stool test or a breath test is used to check whether the bacterium is still there now. If so, the GP usually prescribes a 10-day course of two antibiotics and an acid-reducing medicine, followed by a follow-up stool or breath test; an antibody test is not suitable for that check. With a negative result, the GP looks at other causes of the complaints.

Reliability

How reliable is the test?

The Dutch medical specialists' guideline (FMS) on Helicobacter pylori in children assesses antibody tests (IgG, IgA and IgM) together: in countries where the bacterium is uncommon, the sensitivity was 76 to 80 percent and the specificity 79 to 90 percent, with very low certainty of evidence, and a positive result does not tell whether there is an active infection. Even less is known about IgA separately; the test misses infections more often than IgG. A stool test or a breath test detects the bacterium itself and therefore says more.

What can affect the result?

Not everyone with the bacterium makes detectable IgA; a negative result does not rule out an infection.
Antibodies remain present for a long time after the bacterium has gone; after treatment, a positive result says nothing about the outcome.
There are no agreed cutoff values for IgA; tests differ per laboratory.
The test does not tell whether stomach complaints are caused by the bacterium.

Who it is for

Who is the test useful for?

Useful for

A standalone IgA result says little for any group, because its meaning has been little studied and it does not distinguish between a current and a previous infection. With persistent stomach complaints, a stool test or a breath test says more. In people without stomach complaints, a positive result says little: most carriers have no symptoms.

How common is it?

An estimated 20 in 100 people in the Netherlands have the stomach bacterium, and about 30 to 35 in 100 of people with stomach complaints; the number is falling. In people who grew up in countries around the Mediterranean, Eastern Europe, the Middle East, Asia, Africa, or Central and South America, this can rise to 75 in 100. Most people with the bacterium have no symptoms.

Huisarts & Migrant (knowledge platform for GPs) and Thuisarts.nl

Drawbacks and risks

A positive result can lead to worry or a course of antibiotics, while it is not established that the bacterium is still there.
A negative result can give false reassurance, because IgA misses some of the infections.

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