The most important blood value in celiac disease is anti-tTG of the IgA type, an antibody against tissue transglutaminase. With a gluten intolerance, your immune system often makes this antibody.
So one tube of blood can already explain a lot.
I find that reassuring, because you don't have to think about a heavy scope exam right away. Still, there's a catch. That's why the lab measures a second value too.
Which blood value indicates that you have celiac disease?
Anti-tTG IgA is the first blood value a doctor looks at. It's an antibody your immune system can make when gluten irritates your small intestine. A raised value fits with celiac disease, but doesn't confirm it yet. Extra testing usually follows as a check.
Celiac disease is an auto-immune condition, not a common allergy. According to the Dutch health portal Thuisarts.nl, gluten damages the lining of your small intestine in celiac disease. Because of that, your body sometimes absorbs nutrients less well.
The complaints vary widely. Some people get belly pain or diarrhoea, others mainly fatigue. If you recognise yourself here, see which celiac disease symptoms in adults often get missed.
Some people choose to test for ongoing gut complaints or unexplained fatigue. Others do it because celiac disease runs in the family. What fits you is something you decide with your GP.
How such a test works exactly, you can read in our explainer on the celiac disease test.
What is a normal anti-tTG value?
A normal anti-tTG IgA value sits below the lab's cut-off, often around 7 U/ml. Every lab uses its own limits, so always read the reference on your result. A value below it is usually reassuring. A clearly raised value calls for follow-up with your GP.
Labs often sort the result into categories. Think of negative, weak positive and positive. Those limits differ per test, so a number alone says little.
A result just above the limit is often called weak positive. That can fit with celiac disease, but can have another cause too. Your GP weighs your complaints and the other values as well.
Watch the unit on your result too. Most labs report anti-tTG in U/ml or as an index. So only compare your value with the limit of that same lab.
A strongly raised anti-tTG makes celiac disease more likely. Still, a doctor never makes the diagnosis on one value alone. Usually a gut biopsy or extra blood test is added.
Why does the lab also measure your total IgA?
The lab measures your total IgA to rule out an IgA deficiency. Anti-tTG is itself an IgA antibody. If you have too little IgA, the anti-tTG test can read falsely negative. Your result then looks reassuring, while celiac disease may still be present.
An IgA deficiency happens more often with celiac disease than average. That makes this check extra useful. Without total IgA alongside it, you might miss that pitfall.
You usually don't notice an IgA deficiency yourself. It often gives few complaints, but can still colour your test result. That's why total IgA is standard in many celiac panels.
If your IgA is low, the lab switches to an IgG test. The deamidated gliadin peptide (DGP) IgG test then works as an alternative. That way your result stays usable even with a deficiency.
Overview: the blood values in celiac disease
A celiac work-up usually involves four blood values. Anti-tTG IgA is the first step, total IgA rules out a deficiency, and anti-endomysium (EMA) confirms the result. With an IgA deficiency, DGP IgG steps in. Below you can see what each value measures.
| Blood value | What it measures | What a result can mean |
|---|---|---|
| Anti-tTG IgA | Antibody against tissue transglutaminase of the IgA type (the first step) | A raised value can point to celiac disease and usually calls for follow-up |
| Total IgA | The total amount of IgA in your blood, to rule out an IgA deficiency | With an IgA deficiency the anti-tTG can be falsely negative, so a low value is important to know |
| Anti-endomysium (EMA) IgA | Confirming antibody against endomysium of the IgA type | A positive result makes celiac disease more likely and supports the first test |
| Deamidated gliadin peptide (DGP) IgG | Antibody of the IgG type, as an alternative with an IgA deficiency | Can pick up celiac disease when the IgA tests are unreliable because of a deficiency |
This overview is a tool, not a diagnosis. Only a doctor can place your result in the right context. Use it mainly to understand your own result better.
Do you have to keep eating gluten before the test?
Yes, for a reliable test you usually just keep eating gluten. If you stop with bread and pasta beforehand, the antibodies can drop. Your result then might read falsely reassuring. Many doctors therefore advise you to eat normally until the blood draw.
This is called a gluten provocation or gluten challenge. Your immune system only makes antibodies when gluten comes in. A gluten-free diet therefore makes the test unreliable.
According to the Voedingscentrum, gluten sits mainly in wheat, rye, barley and spelt. If you've already stopped with these products, discuss that with your GP. Sometimes you decide together to eat gluten again for a while first.
How long you eat gluten beforehand differs per situation. Your GP or the gastroenterologist can name a period for this. So don't stop with gluten on your own before a test.
A gluten challenge can flare up your complaints again for a while. That's unpleasant, but it does make the result more reliable. Discuss with your GP how to approach this best.
What your result means for deficiencies
Celiac disease can disturb the uptake of iron and vitamins. Because of that, you sometimes see a low ferritin or a shortage of vitamin B12 or D on a result. Those values explain why you feel so tired. They belong to the bigger picture of an irritated gut.
A low iron is a classic signal with celiac disease. You'll find more context in our article on iron deficiency and anaemia.
Vitamins can get out of balance too. Which signals fit with that, you can find under vitamin deficiency symptoms.
Such a shortage often clears up once the gut recovers. On a gluten-free diet, your gut usually absorbs nutrients better again. Your GP can have the values checked again after a while.
A result is a snapshot, not a final verdict. Together with your story, it gives your GP direction.
What I mainly want to give you: don't look at one number, but at the whole. Anti-tTG and total IgA, together with your complaints, tell the real story.
Unsure about your result? Put it next to your GP and ask explicitly whether an IgA deficiency has been ruled out. Some people choose to do a celiac disease blood test first and discuss the result calmly afterwards.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
References
- Dieterich W, et al. Identification of tissue transglutaminase as the autoantigen of celiac disease. Nat Med. 1997. PMID 9212111.
- Ludvigsson JF, et al. Diagnosis and management of adult coeliac disease: guidelines from the British Society of Gastroenterology. Gut. 2014. PMID 24917550.
- Halfdanarson TR, et al. Hematologic manifestations of celiac disease. Blood. 2007. PMID 16973955.
- Thuisarts.nl. Ik heb coeliakie. Nederlands Huisartsen Genootschap (NHG).
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