Is There a Gluten Intolerance Test?

Currently, there are no reliable gluten sensitivity or gluten intolerance tests. Gluten sensitivity is sometimes mistaken for celiac disease, a gluten-related autoimmune condition. You can be tested for celiac disease, but these tests can't determine if you're sensitive to gluten.

Both gluten intolerance and celiac disease are caused by a reaction to gluten, a protein found in cereal grains like wheat, rye, and barley. They differ in that celiac disease is an autoimmune disorder in which gluten causes the body's immune system to attack the lining of the intestines. In contrast, gluten intolerance does not involve any of the autoimmune proteins (autoantibodies) that are associated with celiac disease.

If you have symptoms of gluten intolerance, your healthcare provider will test you for celiac disease. If celiac disease is not the cause of your symptoms, your provider will need to rule out all the other possible causes before diagnosing you with gluten sensitivity.

This article will go over how gluten intolerance is diagnosed. It also describes what tests are available, including at-home gluten test kits, and when screening is recommended.

Gluten Intolerance Test: Does It Exist?

There are currently no specific tests available for healthcare providers to diagnose gluten intolerance. The diagnosis is based on ruling out all other causes of a person’s symptoms, including celiac disease (for which there are tests).

At-home tests by EnteroLab and EverlyWell are marketed as being able to diagnose gluten sensitivity (non-celiac gluten sensitivity), but the evidence of their reliability is limited.

Causes of Non-Celiac Gluten Intolerance

The causes of gluten intolerance are unknown, but there are some theories.

For example, some research suggests that gluten sensitivity is related to other components found in gluten-containing cereal grains.

One idea is that a collection of short-chain carbohydrates (sugars) called FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) could be involved. These sugars are found in all gluten-containing grains and are not well absorbed in the intestines. When they start to ferment, they cause symptoms of gas, bloating, diarrhea, and abdominal pain.

Other research suggests that proteins called amylase/trypsin inhibitors (ATIs) that are found in all gluten-containing grains could cause an allergic reaction and trigger symptoms of gluten intolerance in some people.

The findings from research studies are not consistent, and it could be that "gluten intolerance" is a broad range of related and unrelated reactions to one or several components in gluten-containing grains.

Symptoms of Non-Celiac Gluten Intolerance

The first symptoms of gluten intolerance vary from one person to the next, both in type and severity. Some people find that the symptoms of a gluten flare show up within an hour of being exposed to gluten, while others may not have symptoms for a day or two after being "glutened."

A gluten flare-up can include gastrointestinal symptoms like bloating (which can be extreme, often called “gluten belly”) as well as non-gastrointestinal symptoms, like skin or cognitive problems.

Troublesome symptoms of gluten intolerance may include:

• Abdominal pain
• Gas
• Bloating
• Diarrhea
• Constipation
• Concentration problems ("brain fog")
• Headache
• Fatigue
  
• Anxiety
• Depression
• Joint pain
• Skin rash
  

Diagnosing Gluten Sensitivity Without a Test

If you or your provider thinks that you are sensitive to gluten, you will start by talking to them about your symptoms and medical history. They will also do a physical exam.

The diagnosis of gluten intolerance will usually involve the following steps:

1. Test for celiac disease. Since the symptoms of celiac disease and gluten intolerance overlap, celiac disease needs to be ruled out first. Unlike with other gluten-related conditions, there is a test for celiac disease. 
2. Rule out other possible causes. If you do not have celiac disease, diagnosing non-celiac gluten sensitivity is a process of elimination. This can involve testing for wheat allergy, irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and other possible causes based on your medical history and symptoms.
3. Start a gluten-free diet. If no explanation can be found, your gastroenterologist will ask you to go on a gluten-free diet for at least six weeks. During that time, you will keep a record of any symptoms you have. If your symptoms get better on the diet, it can be a sign that gluten intolerance was the cause.
   

Ruling Out Other Conditions

The exclusion of possible causes is called a differential diagnosis. This process helps your provider eliminate possible causes from their list until they get to the one that is the most likely explanation for your symptoms. 

A differential diagnosis is important when test results are uncertain and even more important when no tests are available, such as in the case of gluten sensitivity. 

If your provider thinks your symptoms have a gluten-related cause, there are a few conditions that they will want to explore:

• Celiac disease. Celiac disease is aggressive and causes progressive damage to the intestines. There are lab tests that check for celiac disease.
• Wheat allergy: A wheat allergy involves an immune response triggered by an antibody called immunoglobulin E (IgE). A wheat allergy can be differentiated with an IgE blood test. A wheat allergy might also involve sneezing and other respiratory symptoms.
• Irritable bowel syndrome (IBS). IBS mainly affects the lower part of the intestine (the colon), causing mucus in stool and a feeling that your bowels are never empty. There are no tests for IBS but it can be told apart from conditions like celiac disease and gluten sensitivity because it does not involve a reaction to gluten. 
• Inflammatory bowel disease (IBD). IBD like Crohn’s and ulcerative colitis are chronic conditions that can cause severe damage to the intestines. A condition like non-celiac gluten sensitivity does not cause damage to the gut. Rectal bleeding is also common with IBD. A procedure using a flexible scope (endoscope) can be used to diagnose IBD.

Gluten Challenge

A gluten challenge is not the same thing as a gluten-free diet. A gluten challenge is a test used to see if the cause of your symptoms is gluten or something else. It can be an option if there is any uncertainty about the diagnosis.

A gluten challenge takes place after you have been on a gluten-free diet for at least six weeks. 

For the challenge, your provider will do a "blinded" test in which you are either given a food with gluten in it or an equivalent of that food with no gluten. You will not know which is which.

The gluten challenge is done in steps over the course of three weeks:

1. You are given a daily serving of either food with gluten in it or a no-gluten food for one week. Usually, it’s something simple like a muffin. You will eat the food at the same time every day. The rest of the food that you eat during this time will be gluten-free. You will record any symptoms you have, including the time that you have time.
2. You are given a one-week break. During this time, you will continue eating a gluten-free diet.
3. For the final week, you will repeat Step 1 but be given the opposite food (so, if you ate the gluten food the first time, you’ll eat the no-gluten food the second time).

At the end of the challenge, you and your provider will compare the results.

If your symptoms changed by at least 30% between the gluten week and the no gluten week, it could be a sign you have gluten sensitivity. If not, you may need to explore other causes of your symptoms.

Tests for Celiac Disease

Although there are tests to diagnose celiac disease, it’s not always a straightforward process. 

The diagnosis of celiac disease typically starts with blood tests to see if you have specific substances (markers) for the disease. This test is followed by procedures to look at the intestines and take tissue samples that can be looked at in a lab.

Blood Tests

There are several blood tests that can detect markers for celiac disease, including autoantibodies and genetic mutations linked to the disease. These tests include:

• Anti-endomysial antibody (EMA) test. This detects a type of autoantibody that is found in 90% of people with celiac disease. These immune proteins attack connective tissues in the lining of the intestines (endomysium).
• Tissue transglutaminase IgA (TG-IgA) test. This test detects another type of autoantibody involved with celiac disease. These autoantibodies attack a part of the intestine called the lamina propria.
  
• Total serum IgA test. This test tells how much TG-IgA is in a sample of blood. It helps qualify whether your symptoms line up with elevations in TG-IgA levels.
  
• Deamidated gliadin peptide (DGP) test. This test detects a less common autoantibody associated with celiac disease. It is used when TG-IgA and EMA tests are negative.
• HLA-DQ2 and HLA-DQ8 tests. These tests detect specific gene mutations (HLA-DQ2 and HLA-DQ8), that occur in 95% and 5% of people with celiac disease, respectively.

Endoscopy

If the results of the blood tests show celiac disease, the next step is to do procedures to see the insides of the intestines. 

Providers do these tests to look for villous atrophy, a condition in which the finger-like projections in the lining of the intestines (villi) are flattened and destroyed.

There are two ways your gastroenterologist can do these procedures:

• Endoscopy. This procedure is done with the insertion of a long tube with a tiny camera into your mouth and down your throat to see inside your small intestine. It is usually done under monitored anesthesia care (MAC) in a procedure room.
• Capsule endoscopy. This procedure is done by having you swallow a capsule with a mini camera that takes pictures as it passes through your entire digestive tract. It does not require any anesthesia. The capsule eventually exits your body in a bowel movement.

Biopsy

While villous atrophy is a central feature of celiac disease, it can happen with other diseases as well. A sample of tissue will need to be taken from the intestine and looked at in a lab with a microscope (biopsy) to make the diagnosis official. The biopsy sample can be taken during the scope procedures. 

The biopsy is looked at in a lab by a provider called a pathologist. They will compare your sample to the diagnostic criteria for celiac disease that are laid out by the Modified Marsh Classification system.

However, the increasing accuracy of blood tests has led some experts to suggest that strongly positive antibody tests accompanied by less-invasive capsule endoscopy are all that is needed to make a definitive diagnosis of celiac disease.

Other experts say that positive results for both HLA-DQ2 and HLA-DQ8 that are accompanied by symptoms of celiac disease are enough to confirm the diagnosis.

Home Testing for Gluten Sensitivity 

There are several at-home kits you can buy that are said to test for various food sensitivities, including gluten sensitivity. These require either a small sample of stool (poop) or a finger-prick blood sample. Brands of at-home gluten tests include EverlyWell and EnteroLab.

To date, the accuracy of these tests (measured by specificity and sensitivity) is either extremely low or unproven. The cost of these kits (which range from $100 to $400) is usually not covered by health insurance.

Summary

Gluten intolerance or gluten sensitivity (non-celiac gluten sensitivity) shares many symptoms with celiac disease. However, these are not the same conditions. 

Celiac disease is an autoimmune disease that can be diagnosed with a combination of antibody blood tests, genetic blood tests, endoscopy, and an intestinal biopsy.

There are no reliable tests that can diagnose gluten sensitivity. Diagnosing gluten intolerance is a process that takes time and requires patience. The diagnosis is made by ruling out all other possible causes and seeing how your body responds to a gluten-free diet.