Total IgA (Immunoglobulin A)
This is a check that your body makes enough of a key antibody type (IgA), so the coeliac blood tests can be trusted. A small number of people make too little IgA, which can make the main coeliac test read negative even when it shouldn't. So this test is run at the same time to catch that — it is a safety check on the result, not the coeliac test itself.
Standard CareWhat is total iga (immunoglobulin a)?
Immunoglobulin A (IgA) is a class of antibody — a protein the immune system produces to help defend the body, and one that is especially abundant at the body's mucosal surfaces such as the lining of the gut. The total IgA test measures the overall amount of IgA in your blood, rather than any one specific antibody. Total IgA is most often ordered as a partner to coeliac disease testing. The main first-line coeliac test — tissue transglutaminase IgA (tTG-IgA) — is an IgA-based antibody. If your body does not produce enough IgA of any kind (a condition called selective IgA deficiency), that test can come back falsely negative even when coeliac disease is present. Measuring total IgA at the same time tells your GP whether the tTG-IgA result can be trusted, or whether an IgG-based test (such as deamidated gliadin peptide, DGP-IgG) should be used instead. Total IgA can also be measured in other situations — for example, when investigating recurrent infections or as part of a broader immune work-up — but on a coeliac panel its job is to validate the antibody result.
Why is it tested?
In the coeliac setting, total IgA is tested alongside tTG-IgA for one clear reason: to detect the small group of people with coeliac disease who are IgA deficient and would otherwise get a falsely negative screening result. Australian guidance notes the total IgA level detects the roughly 3% of people with coeliac disease who have selective IgA deficiency, and Coeliac Australia recommends it specifically to exclude the 2–3% of people with coeliac disease who are IgA deficient. Outside coeliac testing, a low total IgA can be relevant in its own right — selective IgA deficiency is one of the more common immune differences and is often harmless, but can occasionally be associated with more frequent infections. Your GP interprets a total IgA result in the context of why it was ordered.
Reference range (Australia)
IgA reference intervals vary with age and between laboratories and assays, and IgA is not part of Australia's harmonised chemistry reference intervals. The range printed on your own report is the correct one to use for your result.
Reference intervals vary between laboratories. Always use the range printed on your own report.
What your result means
A low total IgA matters most because of what it means for the coeliac test. If total IgA is low (selective IgA deficiency), the IgA-based tTG-IgA can be falsely negative, so your GP will switch to an IgG-based coeliac test such as DGP-IgG to investigate properly. Selective IgA deficiency is itself often harmless and many people who have it are perfectly well. Sometimes it is associated with more frequent respiratory or gut infections. Your GP will explain what a low IgA means for you, both for the coeliac question and more generally.
A normal total IgA means your IgA-based antibody tests — including the main coeliac test — can be interpreted in the usual way. On a coeliac panel, a normal total IgA alongside a negative tTG-IgA (while eating gluten) makes active coeliac disease less likely.
A raised total IgA is generally non-specific. IgA can rise with infections, inflammation, liver conditions, and some other states. On a coeliac panel, a normal-or-high total IgA simply means the IgA-based coeliac test (tTG-IgA) can be interpreted normally. A high total IgA on its own is rarely acted on. Your GP will read it in the context of why the test was ordered and the rest of your results.
What can affect your result
Several things influence total IgA. Selective IgA deficiency is the most important in the coeliac context: some people inherit a reduced ability to make IgA, which lowers total IgA and can make IgA-based tests (like tTG-IgA) falsely negative. This is precisely why total IgA is measured alongside coeliac serology — to detect the small percentage of people with coeliac disease who are IgA deficient. Age affects IgA levels, which is why reference ranges differ for children and adults. Infections, inflammation, and some liver conditions can raise IgA, while a few medicines and immune conditions can lower it. Because a total IgA result is non-specific on its own, your GP reads it in the context of why it was ordered and the rest of your results.
When to act
On a coeliac panel, if your total IgA is low, your GP will not rely on the tTG-IgA result and will instead use an IgG-based coeliac test (such as DGP-IgG) to investigate — so a low IgA changes how the coeliac question is approached rather than being a problem to act on directly. If a low total IgA was found outside coeliac testing, your GP will consider whether it is an incidental, harmless finding or whether it fits with a pattern of frequent infections that warrants further assessment. A high or borderline total IgA is usually interpreted in context rather than acted on alone. This page is general information and is not a substitute for advice from your GP.
Frequently asked questions
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