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If you've ever opened your patient portal and found a celiac blood test flagged as abnormal, you may have immediately wondered:

Does this mean I have celiac disease?

The answer isn't always as simple as positive or negative.

Celiac disease testing involves looking at several pieces of information together. Your bloodwork is an important part of that process, but the type of test performed, how elevated the result is, your total IgA level, whether you were eating gluten at the time of testing, and sometimes an upper endoscopy with biopsies all help determine what the results actually mean.[1,2]

This article will walk you through the common celiac blood tests, what those confusing numbers and abbreviations mean, and how healthcare professionals use them to decide what may need to happen next.

Before We Talk About the Labs: Are You Still Eating Gluten?

This is one of the most important things to understand about celiac testing.

Celiac blood testing should generally be performed while you are still eating gluten.

Why?

Celiac disease is an immune-mediated disease triggered by gluten. The blood tests used to evaluate for celiac disease are looking for antibodies associated with that immune response.

Once you remove gluten from your diet, those antibody levels can begin to decrease. The intestinal changes caused by celiac disease can also begin to heal.

That means starting a gluten-free diet before your evaluation is complete can potentially affect both your bloodwork and, if one is needed, your intestinal biopsy.[1,2]

If you've already stopped eating gluten, don't assume that you've missed your chance to be tested. Talk with the healthcare professional managing your evaluation. Depending on your situation, additional testing or a clinician-directed gluten challenge may be discussed.

What Blood Tests Are Used to Look for Celiac Disease?

There are several blood tests associated with celiac disease, but they aren't all used in exactly the same way.

For most people, the starting point is tTG-IgA along with a total IgA level.[2,3]

Let's break those down.

tTG-IgA: The Main Celiac Screening Test

tTG-IgA stands for tissue transglutaminase immunoglobulin A.

This is generally the preferred initial blood test used to evaluate for celiac disease because it performs well as a screening test when someone is eating gluten and produces adequate IgA.[2]

When someone has celiac disease and is consuming gluten, the immune system may produce antibodies against tissue transglutaminase.

A positive tTG-IgA raises suspicion for celiac disease.

But here's an important distinction:

A positive result and a diagnosis aren't necessarily the same thing.

How strongly positive the result is matters. Other laboratory results matter. Your clinical history matters. And depending on the situation, additional testing or an intestinal biopsy may be needed before the diagnosis is established.

Total IgA: The Test That's Easy to Overlook

You may see total IgA ordered alongside your tTG-IgA and wonder what it has to do with celiac disease.

Total IgA isn't actually looking for celiac disease.

Instead, it helps determine whether an IgA-based celiac test can be reliably interpreted.

Some people have IgA deficiency, meaning they don't produce normal amounts of immunoglobulin A. If someone has IgA deficiency, an IgA-based celiac test such as tTG-IgA may be negative even when celiac disease is present.[2]

That's why looking at the tTG-IgA without considering the total IgA can sometimes give an incomplete picture.

If IgA is low or deficient, healthcare professionals may turn to IgG-based celiac testing instead.

What About tTG-IgG and DGP-IgG?

Two tests you may see in this situation are:

tTG-IgG — tissue transglutaminase IgG

and

DGP-IgG — deamidated gliadin peptide IgG.

These can be particularly useful when someone has IgA deficiency and therefore cannot rely on the usual IgA-based testing.[2]

DGP testing may also be considered in selected clinical situations, but it isn't simply a “better” version of tTG-IgA. Which tests are appropriate depends on factors such as age, IgA status, and the clinical circumstances.

This is one reason ordering a large collection of celiac antibody tests without understanding what each one means can sometimes create more confusion rather than less.

What Is EMA-IgA?

Another test you may encounter is the endomysial antibody IgA, usually called EMA-IgA.

EMA-IgA is highly specific for celiac disease, meaning a positive result provides strong additional evidence supporting the diagnosis.[2]

It isn't necessarily the first test ordered for every patient. Instead, it may be used as additional or confirmatory testing in certain situations.

EMA becomes particularly important when discussing whether some children with very high tTG-IgA levels can be diagnosed without an intestinal biopsy. We'll come back to that shortly.

A Positive Test Isn't Just “Positive”: Understanding the Upper Limit of Normal

Once you know which celiac antibody was tested, the next question is:

How elevated was it?

This is where you'll hear the term upper limit of normal, abbreviated ULN.

It sounds technical, but the concept is fairly straightforward.

The upper limit of normal is the highest value that a particular laboratory considers within its normal reference range for that test.

For example, imagine your laboratory reports:

tTG-IgA normal range: less than 20 U/mL

In this case, the upper limit of normal is 20 U/mL.

Now imagine your result is:

tTG-IgA: 40 U/mL

Your result is two times the upper limit of normal:

40 ÷ 20 = 2× ULN

If your result is:

tTG-IgA: 200 U/mL

Then:

200 ÷ 20 = 10× ULN

So why not just look at the actual tTG-IgA number?

Because different laboratories may use different assays and different reference ranges.

For example, one laboratory might have an upper limit of normal of 20 U/mL, while another may have an upper limit of normal of 15 U/mL.

A result of 200 at the first laboratory would be:

200 ÷ 20 = 10× ULN

But a result of 150 at the second laboratory would also be:

150 ÷ 15 = 10× ULN

The raw numbers are different, but both results are 10 times their respective laboratory's upper limit of normal.

That's why comparing your tTG-IgA number to someone else's result isn't particularly useful unless you also know the reference range used by each laboratory.

And there's another reason this calculation matters.

How many times above the upper limit of normal your tTG-IgA is can influence what happens next in the diagnostic process.

What Does a Mildly Positive tTG-IgA Mean?

This is where celiac testing becomes more nuanced.

A tTG-IgA that is just above the laboratory's reference range isn't interpreted the same way as a tTG-IgA that is many times the upper limit of normal.

In general, the higher the tTG-IgA level, the greater the likelihood that celiac disease is present.[2]

But a mildly elevated tTG-IgA doesn't automatically establish the diagnosis.

Your healthcare professional may consider the degree of elevation, your symptoms and risk factors, total IgA, additional antibody testing when appropriate, and whether an upper endoscopy with biopsies is needed.

This is also why seeing a red “H” next to a result in your patient portal doesn't tell the entire story.

It tells you that the result is above that laboratory's reference range.

It doesn't tell you, by itself, why it's elevated or whether you definitely have celiac disease.

So Where Does the Endoscopy Fit In?

Once bloodwork suggests celiac disease, the next question is often whether an upper endoscopy with small-intestinal biopsies is needed.

An upper endoscopy, also called an EGD, involves passing a thin, flexible scope through the mouth, stomach, and into the first portion of the small intestine.

For celiac diagnosis, however, what's especially important isn't simply what the intestine looks like during the procedure.

It's the biopsies.

Celiac-related changes can be microscopic, so the intestine doesn't necessarily have to look obviously abnormal during the endoscopy.

Small tissue samples are taken from different areas of the duodenum and examined under a microscope. The pathologist looks for changes associated with celiac disease, which may include:[1,2]

• Increased intraepithelial lymphocytes: An increased number of immune cells, called lymphocytes, within the lining of the small intestine. This can be an early sign of an immune response, but it is not specific to celiac disease and can occur with other conditions.
• Crypt hyperplasia: The crypts are small structures located between the intestinal villi where new intestinal cells are produced. With ongoing inflammation and injury, these crypts can become deeper or enlarged as the intestine works to replace damaged cells.
• Villous shortening or villous atrophy: Villi are the tiny, finger-like projections lining the small intestine that increase its surface area and help absorb nutrients. With active celiac disease, these villi can become shortened, flattened, or damaged. More significant flattening is called villous atrophy and can reduce the intestine's ability to absorb nutrients normally.

You may also see a Marsh classification mentioned on your pathology report. The Marsh classification is a system used to describe the degree and pattern of microscopic changes seen in the small intestine.

These biopsy findings are interpreted together with your celiac bloodwork, medical history, symptoms, and other clinical information. One finding by itself—such as increased intraepithelial lymphocytes—doesn't necessarily establish a diagnosis of celiac disease.

Do Adults With Positive Celiac Bloodwork Need an Endoscopy?

For adults, upper endoscopy with duodenal biopsies remains an important part of the standard diagnostic approach when celiac disease is suspected.[1,2]

This is especially important because not every positive antibody test means celiac disease, and intestinal biopsy can provide additional evidence supporting the diagnosis.

However, the role of biopsy-free diagnosis in adults continues to evolve.

Very strongly positive tTG-IgA results—particularly results greater than 10× ULN—have a high likelihood of representing celiac disease. NIDDK notes that when endoscopy is not feasible, a combination of tTG-IgA greater than 10× ULN and a positive EMA-IgA on a subsequent blood sample may provide a reliable diagnosis, while also noting that this has not traditionally been endorsed as the routine diagnostic approach for adults.[2]

So if you're an adult and your tTG-IgA is 10× ULN, don't automatically assume:

“My number is high enough, so I don't need a biopsy.”

That's a conversation to have with the healthcare professional managing your evaluation.

Children Can Have a Different Diagnostic Pathway

Children are an important exception to the idea that everyone with suspected celiac disease needs an intestinal biopsy.

The European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) has established a no-biopsy diagnostic pathway for certain children.[3]

One of the key criteria is:

tTG-IgA ≥10× the upper limit of normal.

This is exactly why understanding ULN is so important.

Let's go back to our earlier example.

If the laboratory's upper limit of normal is 20 U/mL:

20 × 10 = 200 U/mL

A result of 200 U/mL would therefore equal 10× ULN.

But the tTG-IgA level isn't the only requirement.

Under the ESPGHAN no-biopsy pathway, EMA-IgA must be positive on a second blood sample. The patient and family should also be involved in the decision about using the no-biopsy approach.[3]

If the tTG-IgA is positive but less than 10× ULN, ESPGHAN recommends duodenal biopsies rather than using the no-biopsy pathway.[3]

So a very high tTG-IgA in a child doesn't mean you should simply cancel the gastroenterology appointment. It means the child's healthcare team can determine whether the specific criteria for a no-biopsy diagnosis have been met.

What If the Bloodwork Is Negative but Celiac Disease Is Still Suspected?

A negative tTG-IgA makes celiac disease less likely, but it doesn't answer every situation.

This is where the rest of the laboratory work becomes important.

Was the total IgA normal?

Was the person eating gluten when the test was performed?

Is there IgA deficiency?

Is there a strong family history or another reason the healthcare professional has a high suspicion for celiac disease?

NIDDK notes that a small percentage of people with celiac disease have negative serologic testing.[2] If clinical suspicion remains high despite negative bloodwork, additional evaluation—including intestinal biopsy in some circumstances—may still be appropriate.

What If the Bloodwork Is Positive but the Biopsy Is Normal?

This can happen too, and it doesn't necessarily mean that one test was “wrong.”

There are several questions that may need to be considered.

Was the person eating enough gluten before the endoscopy?

Were enough biopsies taken?

Were biopsies obtained from the appropriate areas of the duodenum?

How strongly positive were the celiac antibodies?

Could another condition be contributing to the abnormal bloodwork?

In some situations, a person may have positive celiac serology without the intestinal damage required for a classic biopsy-confirmed diagnosis. You may hear the term potential celiac disease used in certain circumstances.

These cases often require individualized follow-up rather than trying to interpret one laboratory value by itself.

What About Genetic Testing?

You may also hear about genetic testing for HLA-DQ2 and HLA-DQ8.

Genetic testing works differently from antibody testing.

A positive genetic test does not diagnose celiac disease.

Many people carry HLA-DQ2 or HLA-DQ8 and will never develop celiac disease.

Where genetic testing can be particularly helpful is in ruling celiac disease out in selected situations. Because the vast majority of people with celiac disease carry compatible HLA genes, not having the associated genetic susceptibility makes celiac disease very unlikely.[1]

Genetic testing can therefore be useful when the diagnosis is unclear—for example, when someone has already been gluten-free and their previous testing doesn't provide a clear answer.

Putting the Celiac Lab Work Together

Instead of looking at one result and asking, “Is this positive?”, it can be more helpful to think of celiac testing as a series of questions.

Was the person eating gluten when they were tested?

Then:

What was the tTG-IgA?

Was a total IgA checked, and was it normal?

How elevated was the tTG-IgA compared with that laboratory's upper limit of normal?

Is additional serology, such as EMA-IgA or IgG-based testing, appropriate?

Does the person need an upper endoscopy with duodenal biopsies?

And finally:

Do all of the pieces fit together?

That's ultimately what celiac diagnosis is about.

Not one number.

Not one symptom.

And not simply whether something is flagged red in your patient portal.

The Bottom Line

For most people being evaluated for celiac disease, tTG-IgA and total IgA are important starting points.

The tTG-IgA result should be interpreted relative to the laboratory's reference range—not simply by looking at the raw number.

If total IgA is low or deficient, IgG-based testing may be needed.

EMA-IgA can provide additional diagnostic information and plays an important role in established no-biopsy pathways.

For adults, duodenal biopsy remains an important part of the diagnostic process in many cases. For children who meet specific criteria—including a tTG-IgA ≥10× ULN and positive EMA-IgA on a second blood sample—a no-biopsy diagnosis may be possible under established pediatric guidelines. [1–3]

Most importantly, don't start a gluten-free diet simply because you see an abnormal celiac test in your patient portal.

Complete the diagnostic evaluation first whenever possible.

Once gluten is removed, both the antibody response and intestinal damage can begin to improve, which may make getting a clear diagnosis more difficult. [1,2]

Understanding your celiac testing doesn't mean you have to diagnose yourself. It means you can walk into your next appointment with a better understanding of what was tested, what your results may mean, and what questions you may want to ask.

What Would You Like to Understand Better?

Celiac disease comes with a lot of questions—and sometimes the medical terminology makes the answers harder to understand than they need to be.

Is there something about celiac disease you've been wondering about? A lab result you don't understand? A topic you've heard conflicting information about? Or something about living gluten-free that you'd like to see explained?

I'd love to hear your questions and what topics you'd like to see covered here at The Whole Celiac. Your questions can help shape future articles and conversations, so we can focus on what matters to people living with celiac disease and the people who support them.

Email hello@thewholeceliac.com.

Sources & Further Reading

1. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Diagnosis of Celiac Disease.
Overview of celiac serologic testing, intestinal biopsy, genetic testing, and the diagnostic process.

https://www.niddk.nih.gov/health-information/digestive-diseases/celiac-disease/diagnosis

2. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Celiac Disease Tests.
Healthcare-professional resource covering tTG-IgA, total IgA, EMA, IgG-based testing, intestinal biopsy, seronegative disease, and interpretation of strongly positive serology.

https://www.niddk.nih.gov/health-information/professionals/clinical-tools-patient-management/digestive-diseases/celiac-disease-health-care-professionals

3. Husby S, Koletzko S, Korponay-Szabó I, et al. European Society Paediatric Gastroenterology, Hepatology and Nutrition Guidelines for Diagnosing Coeliac Disease 2020. Journal of Pediatric Gastroenterology and Nutrition. 2020;70(1):141–156.

https://pubmed.ncbi.nlm.nih.gov/31568151/

This article is intended for educational purposes only and is not a substitute for individualized medical advice, diagnosis, or treatment. Talk with your healthcare professional about the testing and diagnostic approach appropriate for you or your child.