Blood draw
Celiac Disease: IgA/IgG Transglutaminase
IgA and IgG against transglutaminase; for celiac disease screening.
€ 78,00
All tests
Gut · Blood
Transglutaminase (tTG) IgG
Celiac antibodies of the IgG type; mainly of value in people who make too little IgA, only reliable if you eat gluten.
At a glance
- Measured in blood
- In 1 test panel
- No special preparation
Explanation
Transglutaminase (tTG) IgG: what is measured?
In celiac disease, the immune system makes antibodies against tissue transglutaminase (tTG), a protein in the gut wall, after eating gluten. These are usually antibodies of the IgA type. Some people naturally make (almost) no IgA; for them, the usual tTG IgA test is not usable. This test measures the same antibodies, but of the IgG type.
What can it detect?
- Celiac disease in people with a lack of IgA (IgA deficiency)
- Limited: additional information alongside tTG IgA in people with a normal IgA
Result
What does the result mean?
Transglutaminase (tTG) IgG too high
A raised tTG IgG in someone with an IgA deficiency fits celiac disease. In someone who makes IgA normally, a raised tTG IgG alongside a normal tTG IgA says little; the IgA test then takes precedence. Symptoms that may go with celiac disease are diarrhea or constipation, abdominal pain, a bloated feeling, weight loss, tiredness and anemia. The diagnosis is not made on this test alone.
Transglutaminase (tTG) IgG too low
A low or negative value makes celiac disease less likely, but does not rule it out: the IgG test misses some people with celiac disease. This test is also only reliable if you ate gluten normally in the weeks before. In someone with a normal IgA, a negative tTG IgG adds nothing to tTG IgA.
After an abnormal result
With a raised tTG IgG, especially with an IgA deficiency, the GP refers you to the gastroenterologist for an endoscopy with biopsies of the small intestine. With an unclear result, the GP can also have total IgA measured.
Reliability
How reliable is the test?
According to the Dutch Society for Clinical Chemistry (NVKC), measuring IgG antibodies against tTG is only useful in people with an IgA deficiency; for everyone else, tTG IgA is the recommended test. The Dutch medical specialists' guideline (FMS) on celiac disease advises always taking biopsies of the small intestine in case of an IgA deficiency. In the studies in the guideline, the median sensitivity of tTG IgG was 63 percent and the specificity 99 percent: a positive result is therefore usually correct, but a negative result misses relatively many people with celiac disease.
What can affect the result?
- The test is only reliable if you eat gluten; on a gluten-free or low-gluten diet, the result can be falsely negative.
- Without measuring total IgA, it is not known whether someone has an IgA deficiency, and therefore whether this is the right test to go by.
- Measurement methods and cut-off values differ between laboratories.
Who it is for
Who is the test useful for?
Useful for
Mainly useful in people with suspected celiac disease who have an IgA deficiency, or in whom tTG IgA is negative while the symptoms do fit. For everyone else, tTG IgA is the first test. If you already eat gluten-free, this test is of little use.
How common is it?
About 1 in 100 people in the Netherlands has celiac disease, more often women than men; in people with a parent, brother or sister with celiac disease, about 10 in 100. According to the Dutch Society for Clinical Chemistry (NVKC), an IgA deficiency without symptoms occurs in about 1 in 700 people, and more often in people with celiac disease.
Thuisarts.nl (NHG) and the NVKC
Drawbacks and risks
- A negative IgG test can give false reassurance in someone with an IgA deficiency, because the test misses some people with celiac disease.
- If you start eating gluten-free yourself after a positive result, before the diagnosis has been made, the follow-up testing becomes unreliable.
Get tested
Transglutaminase (tTG) IgG: test panels
Transglutaminase (tTG) IgG is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
More about risks and results- FMS Richtlijnendatabase: Coeliakie en glutengerelateerde aandoeningen, module Serologische diagnostiek bij volwassenen
- NVKC Zinnige Diagnostiek: Overwegingen bij screenend bloedonderzoek naar coeliakie
- Nederlandse Coeliakie Vereniging: Goed voorbereid naar de huisarts
- NHG-Standaard Voedselovergevoeligheid en coeliakie
- Thuisarts.nl: Ik heb coeliakie
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