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What Is Celiac Disease?

Celiac disease is a disorder in which the body’s immune system attacks the lining of the small intestine after a person consumes gluten. Gluten is a protein found in wheat, barley, rye, and other grains. Other products that may contain gluten include food colorings and thickeners, vitamins, toothpaste, and products for the skin and hair.

This disorder is called an autoimmune disorder because a person’s own immune system causes harm to the body. Untreated celiac disease leads to inflammation that damages the small intestine, which prevents a person from properly absorbing nutrients that the body needs.

The symptoms of celiac disease can vary significantly from person to person. Some patients have gastrointestinal symptoms like diarrhea, constipation, or abnormal stool. The inability to absorb nutrients can cause other symptoms such as weight loss, fatigue, skin rashes, and tooth damage. People with celiac disease may also have headaches, mood changes, and other neurological effects.

Sometimes celiac disease causes a mix of one or more of these symptoms, but other times it causes no symptoms at all. The wide range of possible symptoms makes it more challenging to diagnose celiac disease, especially because many of the symptoms can be caused by other conditions. As a result, people with celiac disease often go many years before they are diagnosed.

Celiac disease can occur in people of any age when they are exposed to gluten. It is estimated that as many as 1 in 100 people worldwide have celiac disease, although it occurs more often in people from certain geographic regions.

Celiac disease is believed to be caused by a combination of genetic and environmental factors. Almost all people with celiac disease have certain genetic variations that predispose them to an autoimmune reaction when they consume gluten. However, most people with these genetic variations never develop celiac disease.

It is not known why one person develops celiac disease and another person doesn’t, but the risk is higher in people who have a first-degree relative with the condition. Celiac disease is also more common in people who have other autoimmune disorders like type 1 diabetes.

Most people with celiac disease need to follow a gluten-free diet in order to prevent symptoms and avoid long-term complications that are associated with inflammation and damage to the small intestine.

How is celiac disease different from a wheat allergy?

Wheat and other food allergies activate different parts of the immune system compared to celiac disease. For that reason, celiac disease is not considered to be a food allergy. Instead, it is an autoimmune disorder triggered by exposure to gluten.

Food allergies cause different symptoms such as difficulty breathing and hives and, unlike celiac disease, do not cause damage to the small intestine.

How is celiac disease different from gluten sensitivity?

Gluten sensitivity, sometimes called gluten intolerance, occurs when a person has digestive or other problems after eating gluten. While the symptoms of gluten sensitivity can be similar to celiac disease, gluten sensitivity does not involve a reaction by the immune system. For this reason, gluten intolerance may also be called non-celiac gluten sensitivity (NCGS).

People with celiac disease have an autoimmune response to gluten that damages the small intestine. This does not occur in people with gluten sensitivity.

The Role of Celiac Disease Tests

Celiac disease testing is used to detect the condition and evaluate how it is affecting a person’s overall health. The main purposes of testing are for diagnosis, monitoring, and screening in celiac disease.

Diagnosis is the process of finding the cause of a person’s symptoms. In order to diagnose celiac disease, doctors use several types of tests that can detect signs of an autoimmune reaction to gluten. Other tests may be used to determine the likelihood that a person has celiac disease or to look for health complications that can be caused by celiac disease.

Monitoring is testing that is done to track how a patient’s condition is changing. For celiac disease, this is typically performed to see if treatment is working. Monitoring tests can help demonstrate how well a patient is following a gluten-free diet and assess whether they have any health problems related to malabsorption of nutrients by the small intestine.

Screening is looking for signs of a disease in people who have not shown any symptoms. Although not routine, doctors may recommend tests to screen for celiac disease in people with a family history of the disease or other risk factors that make it more likely for them to have the condition.

Patients should talk with their health care provider to understand the role of testing in their situation.

Who should get testing?

Because celiac disease testing can be used in different ways, the decision about who should get testing depends on whether testing is for diagnosis, monitoring, or screening.

Diagnosis

Testing for celiac disease is typically recommended in people who have symptoms that could be caused by the condition. Examples of gastrointestinal symptoms that may prompt celiac disease testing include:

  • Ongoing or persistent diarrhea or constipation
  • Abdominal bloating or pain
  • Unexpected weight loss

Testing may also be advised for other signs or symptoms that occur without any other explanation, such as:

Many of these symptoms can be caused by other health conditions, so diagnostic testing can help determine if they are the result of celiac disease or another problem.

Monitoring

People who have already been diagnosed with celiac disease frequently have ongoing monitoring tests. These tests are performed several weeks to months after the patient has started on a gluten-free diet in order to assess how well the treatment is working. Periodic testing can also evaluate health problems related to celiac disease.

Screening

There are no widely accepted guidelines for when adults who do not have symptoms should have screening tests for celiac disease.

In general, screening is not recommended in people without symptoms if they also do not have known risk factors for celiac disease. People who have one or more risk factors, such as having another autoimmune disorder or a close relative with celiac disease, should talk with their doctor about the benefits and downsides of screening in their case.

Getting test results

Some types of celiac disease tests provide rapid results, while others may take several business days. In many cases, doctors prescribe several tests and the results of these tests are reviewed together by the doctor.

Initial testing for celiac disease may report results as either positive or negative. Positive results indicate that celiac disease is likely, and negative results mean that celiac disease is unlikely. In some cases, the results may be inconclusive. Other possible results of celiac disease testing include:

  • Potential celiac disease: Results may show that a person has “potential” celiac disease. This means that there was a discrepancy between different test results. People with potential celiac disease may have repeat testing if they experience any ongoing symptoms.
  • Silent celiac disease: Another possible test result is a diagnosis of “silent” celiac disease. This means that multiple tests show signs of celiac disease in testing, but the patient has no symptoms of the condition. People with silent celiac disease may have periodic testing to track any changes in the disorder.

Understanding the significance of celiac disease testing requires careful interpretation by a doctor or a specialist called a gastroenterologist. For this reason, patients should always review the results of their tests with their health care provider.

Types of Celiac Disease Tests

Celiac disease testing frequently involves a combination of tests that are used to look for signs of celiac disease, damage to the small intestine, and difficulty in absorbing nutrients from food. A doctor decides which tests to prescribe based on a person’s risk of having celiac disease and whether they follow a gluten-free diet. Avoiding gluten can affect test results, so doctors typically prefer to do initial testing in people who are currently consuming gluten.

The following sections provide additional information about different types of celiac disease tests.

Physical exam and health review

An initial visit with the doctor usually includes a physical exam and a review of a patient’s health history and present symptoms.

During the physical exam, the doctor can look for signs of celiac disease such as skin rashes or swelling in the abdomen. They may also listen to the abdomen with a stethoscope and check for nutritional problems like unexpected weight changes or tooth damage.

The doctor will also ask about symptoms a patient has experienced as well as their personal medical history. A patient’s family health history is used to determine if any close relatives have celiac disease. Doctors may ask about a person’s typical diet and whether they currently eat gluten.

Based on these initial examinations, the doctor can decide how likely it is that a patient has  celiac disease and whether further testing is appropriate.

Antibody blood testing

Antibody blood tests are usually the first tests that are ordered to diagnose celiac disease. These tests look for proteins created during the body’s immune response, known as antibodies, that are present in most people with celiac disease.

It is normal for the body to generate many different kinds of antibodies, which are also called immunoglobulins. Antibodies have specific targets to help coordinate an immune response against a particular threat, such as a bacteria or virus.

In celiac disease, antibodies are developed that target the body’s own tissue in the small intestine. These are known as autoantibodies. Celiac disease testing may involve several autoantibody tests including:

  • Anti-tissue transglutaminase antibodies immunoglobulin A (tTG-IgA): Testing for the presence of tTG-IgA is the preferred antibody test for celiac disease. This test is widely available and able to identify most people with celiac disease.
  • Anti-endomysial antibody immunoglobulin A (EMA-IgA): Testing for EMA-IgA antibodies is very accurate but takes longer to perform and can be more challenging to interpret. For that reason, EMA-IgA testing is often used when confirmation of the results of other antibody tests is needed.
  • Total IgA: Some people with celiac disease have low levels of all types of immunoglobulin A antibodies, which is called IgA deficiency. This can cause low levels of tTG-IgA and EMA-IgA antibodies despite the presence of celiac disease. Measuring total IgA can detect IgA deficiency and enhance interpretation of other antibody tests.
  • Anti-tissue transglutaminase antibodies immunoglobulin G (tTG-IgG): tTG-IgG is a different type of antibody that targets the small intestine. The tTG-IgG test is generally only used for celiac disease testing in patients with low total IgA.

Celiac disease blood tests can also look for antibodies that target gliadin, which is part of the gluten protein. These antibodies are known as anti-deamidated gliadin peptide (DGP) antibodies and include DGP-IgA and DGP-IgG. Tests for these antibodies are most often used in people with low total IgA levels or in children.

Celiac disease antibody tests find elevated antibody levels in over 95% of people who have the condition. High antibody levels are very uncommon in people who do not have celiac disease. As a result, a positive antibody test is usually required to diagnose a person with celiac disease.

However, antibody tests may also have limitations. For example, antibodies may not be detected in people with celiac disease who are on a gluten-free diet. Because of this, diagnostic blood testing is typically done in people who have gluten in their diet.

For monitoring tests, the decrease in antibody levels on a gluten-free diet helps determine how well treatment is working.

Endoscopy and biopsy

Testing to closely examine the small intestine is frequently part of celiac disease testing. This involves two components:

  • Endoscopy: This is a procedure in which a flexible tube with an attached camera is inserted through the mouth into the gastrointestinal system. Through the camera, the doctor can look for signs of inflammation and damage to the small intestine.
  • Biopsy: During an endoscopy, several pieces of tissue can be removed from the small intestine so that it can be analyzed under a microscope. Certain abnormalities in the tissue sample are an important indication of celiac disease.

An endoscopy and biopsy are usually performed after an initial blood antibody test is positive. A positive result on the biopsy is needed to confirm a diagnosis of celiac disease. A repeat endoscopy and biopsy may be performed in some patients as a way of monitoring the condition.

Video capsule endoscopy

Some patients may not be able to have an endoscopy and small intestine biopsy. In these patients, doctors may consider using another test called video capsule endoscopy (VCE) to look at the lining of the small intestine.

In this procedure, the patient swallows a capsule about the size of a pill that contains a camera. As it moves through the intestines, the camera takes pictures that can be reviewed to look for indications of damage to the small intestine consistent with celiac disease. However, no tissue sample can be removed during a video capsule endoscopy, so no definitive biopsy analysis can be performed.

Skin biopsy

In patients with a skin rash, a skin biopsy may be used to remove a sample so that it can be analyzed under a microscope. About 10% of people with celiac disease develop a particular type of painful skin rash known as dermatitis herpetiformis.

People who are diagnosed with dermatitis herpetiformis and have positive antibody blood tests can be diagnosed with celiac disease without having an endoscopy and small intestine biopsy.

Genetic testing

Almost all people with celiac disease have a genetic variation in one or more specific genes. These genes are known as HLA-DQ2 and HLA-DQ8. However, most people who have these gene variants never develop celiac disease.

As a result, genetic tests for these variants are used primarily to rule out celiac disease. People who do not have these gene variants virtually never have celiac disease.

Genetic testing can be performed with a blood sample or a cheek swab. This testing, also known as HLA typing, is most frequently used to rule out celiac disease in certain situations such as:

  • When a patient may have celiac disease but is on a gluten-free diet that can cause blood antibody tests to be negative
  • When the results of antibody tests and endoscopy and biopsy have contradictory results
  • When a patient cannot have an endoscopy and biopsy
  • When someone has a family history of celiac disease that places them at higher risk of the condition
  • When treatment for celiac disease is not effective and the initial diagnosis needs to be reconfirmed

Testing for complications

Because celiac disease is associated with a wide range of symptoms and potential complications, people with the condition typically have additional tests to evaluate their overall health. This type of testing may be done soon after an initial diagnosis and periodically after treatment.

Examples of tests that may be ordered include:

  • Complete blood count (CBC): This blood test measures the amounts of different types of blood cells and can detect anemia in people with celiac disease that is caused by insufficient nutrient absorption.
  • Cholesterol testing: People with celiac disease may have abnormal levels of cholesterol, so it is common to conduct a lipid panel test to check cholesterol levels in the blood.
  • Thyroid testing: Celiac disease can occur along with other autoimmune disorders that cause damage to the thyroid, so thyroid function testing may be used to measure blood levels of thyroid hormones.
  • Comprehensive metabolic panel (CMP): This blood test checks for abnormalities in the levels of electrolytes like calcium, potassium, and sodium that enable proper cell function and maintain the body’s acid-base balance. A CMP also takes measurements to assess liver and kidney health.
  • Testing nutrient levels: Because celiac disease can cause malabsorption of nutrients in the intestine, testing is frequently used to check levels of vitamins and minerals such as vitamin B12, folate, vitamin A, vitamin D, vitamin E, iron, ferritin, copper, zinc, and carotene.
  • Prothrombin time: Prothrombin time measures how long it takes for the plasma in the blood to clot. This test is done because people with celiac disease may have slower prothrombin time.
  • Bone density testing: Poor absorption of minerals can cause thinning of bones in people with celiac disease, so it is common to have bone density testing with a DXA scan. This scan can show if a person is at a higher risk of bone fractures.

Further follow-up tests may be ordered based on a patient’s specific symptoms and their results from initial testing for health complications of celiac disease.

Getting Tested for Celiac Disease

Celiac disease testing is normally ordered by a doctor and is usually performed in a medical setting like a doctor’s office or hospital.

At-home testing

At-home options are available for certain types of celiac disease testing. However, several important celiac disease tests are not available at home, so at-home test kits cannot diagnose celiac disease.

At-home celiac disease tests are self-collection tests, which means that a test sample is taken at home and mailed to a laboratory for analysis. These tests generally fall into two categories:

  • At-home antibody testing: These tests look for one or more antibodies in the blood that are associated with celiac disease. To obtain the test sample, a finger prick with a tiny needle included in the test kit is used to apply several drops of blood to a special test paper that is then mailed to a laboratory.
  • At-home genetic testing: Genetic tests look for specific gene variants in a person’s DNA that occur in almost all people who have celiac disease. To take the test, a swab is taken from the inside of the cheek, and the swab is sent to a laboratory for genetic testing.

Neither antibody tests nor genetic tests can definitively determine whether a person has celiac disease, so at-home tests should not be used in lieu of discussing health concerns with a doctor. Results from at-home celiac disease tests should also be shared with a doctor who can help explain their overall significance.

Comparing Tests

Celiac disease testing in adults vs. children

Celiac disease can affect children and adults. The approach to testing and the tests that are used are generally similar for both groups, but some differences include:

  • Screening tests are more likely to be recommended in children over three who have no symptoms but are at an elevated risk of celiac disease. This increased risk may be because they have another autoimmune disorder, Down Syndrome, or a family history of celiac disease.
  • In children, a diagnosis of celiac disease is usually only confirmed if a child shows a positive response to treatment with a gluten-free diet.
  • For some children, it is possible to make an initial diagnosis without an endoscopy and biopsy if they have very high blood antibody levels and the presence of typical celiac disease symptoms.

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