TTG IgA: The First-Line Celiac Screening Marker

Celiac disease is an autoimmune disorder primarily affecting the small bowel. It is caused by an immune reaction to gluten-containing foods consumed in the diet in people who are genetically susceptible. Around 1 in 100 people have celiac disease, although people with affected family members are at higher risk.

Untreated celiac disease can lead to vitamin and mineral malabsorption, osteoporosis, and lymphoma of the small intestine. However, these conditions can be prevented by maintaining a gluten-free diet.

The anti-tissue transglutaminase (anti-TTG) IgA blood test is the first step in testing for celiac disease. This test is very effective at distinguishing between people who have celiac disease and people who don’t.

Not everyone with celiac disease has symptoms, and over half of cases are missed. Because untreated celiac disease has several health consequences, it is important to make the diagnosis early. The anti-TTG IgA test can also be helpful for determining whether people with gluten-related gastrointestinal symptoms have celiac disease or non-celiac gluten sensitivity.

The anti-TTG IgA test is typically reported as either negative or positive, with a cutoff set by the performing laboratory. The positive predictive value of the test increases with higher titres, with an anti-TTG IgA titre of 10x above the cutoff being strongly predictive of celiac disease. There is no evidence to support an optimal range for this test.

It is recommended to use the cutoffs specified by the performing laboratory, which is 15.0 U/mL for our lab testing partner: anti-TTG IgA levels below 15.0 U/mL are considered normal (optimal), while levels at or above 15.0 U/mL are considered elevated (at risk).

anti-TTG IgA should be measured concurrently with an IgA level to rule out IgA deficiency, which can result in a false negative anti-TTG IgA titre. Our lab testing partner's reference range for IgA is: 0.80 g/L is low, 0.80–4.90 g/L is normal, and greater than 4.90 g/L is high.

Note: The celiac screen test is most accurate when you have a diet that includes gluten. People who take the test while on a gluten-free diet may have a false negative result. If you were on a gluten-free diet when you took this blood test, additional testing may be recommended.