Celiac Disease And The Tests That Detect It

Celiac disease is an autoimmune disorder that disrupts the body’s ability to digest gluten. Gluten is a dietary protein in wheat products; the disease also affects some related proteins found in barley and rye. Celiac causes the small intestine to become inflamed when exposed to gluten; the inflammation can damage or destroy the lining of the intestine.

The intestinal wall is studded with villi, projecting folds of tissue that increase the surface area available to absorb nutrients (including vitamins, fluids, minerals, and electrolytes) from food. When a person with celiac disease eats gluten, it triggers the body’s immune system. Immune cells will attack the intestinal villi. This immune response usually, but not always, involves the production of auto-antibody proteins by the immune system.

The harmful immune response and autoantibody production will continue if the individual is exposed to gluten and the other relevant proteins. Over time, the immune system can do enough damage to the intestinal villi to reduce the body’s ability to absorb nutrients. This results in the affected person developing symptoms associated with malnutrition.

Celiac disease occurs all over the world, with individuals of European descent being more likely to experience it. In the United States, celiac disorder occurs at a rate of one case in 100 to 150 individuals. Women are slightly more susceptible than men. While celiac can develop at any age, it is most seen in infants or people between 30 and 50 years of age.

At one time, adult celiac disease was much less common and infant celiac disease was much more serious. The disease’s demographics have changed, with the frequency of adult cases growing more abundant in recent years.

Celiac disorder is an inherited condition, but it appears that some event — physical, environmental, or psychological — is required to trigger the disease. The mechanism that causes celiac to manifest is not yet fully understood by doctors.

Data from the National Digestive Diseases Information Clearinghouse points out the genetic component of celiac disease. Celiac disorder is more common among the first-degree relatives (parents, children, and siblings) of individuals who already have it. Celiac disorder occurs in approximately 4 to 12 percent of first-degree relatives of those who already have it.

Celiac Disease Symptoms

Researchers estimate that there may be as many as 20 million people with celiac around the world, with two to three million of them in the United States. Exact figures are difficult to come by as 90 percent of the people who have celiac disorder in the US go undiagnosed. One fact that makes the disease hard to pin down is that individual sufferers’ symptoms can vary widely.

How celiac disorder manifests tends to vary based on the individual’s age and physical development. Digestive symptoms are more common in infants and children. At the same time, adult sufferers tend to experience symptoms affecting other parts of the body. The symptoms of celiac disease can also be caused by many other medical conditions, such as a food allergy. This leads to many cases going undiagnosed for years.

These are all common symptoms of celiac disease:

  • Abdominal bloating and pain
  • Chronic constipation or diarrhea
  • Vomiting
  • Greasy, foul-smelling stool
  • Susceptibility to bruising and bleeding
  • Pain in bones and joints
  • Fatigue
  • Mental focus problems
  • Oral ulcers
  • Dental enamel defects
  • Osteoporosis
  • Weight Loss
  • Anemia/iron deficiency that cannot be corrected via supplements

In children, celiac disorder can retard growth and development, delay puberty, and cause short stature. Adults with celiac disease may suffer from reproductive issues, including infertility.

People living with Celiac disease also often develop dermatitis herpetiformis, a skin condition that raises itchy blisters.

Celiac disorder is associated with an increased risk of developing intestinal lymphoma (cancer).

Testing For Celiac Disease

The first step in making a celiac disease diagnosis is to test for the presence of specific autoantibodies associated with the condition. A biopsy is performed to confirm the diagnosis if auto-antibody tests suggest celiac disease’s presence. Further auto-antibody testing can be used to monitor the progression of celiac disease and its treatment, which is often done for symptomatic patients. Auto-antibody testing can also be used to screen relatives after one family member has been diagnosed.

There are two classes of intestinal autoantibodies that can be detected, IgA and IgG. IgA tests are more specific, leading to them being heavily preferred in diagnosing celiac disease. IgA is the most common antibody found in gastrointestinal secretions. IgG tests are still useful because a small fraction of celiac disease patients (two to three percent) also have an IgA deficiency.

Common IgA tests for celiac disease include the following:

Testing for anti-tTG antibodies in the blood is the most sensitive and specific way to detect celiac disease, so this is usually the first test performed. There is a less-sensitive test for anti-tTG in the IgG class; this usually is only used if the individual is IgA-deficient.

This test is often included in the celiac testing process because it will detect the presence of an IgA deficiency.

People with celiac disease who test negative for anti-tTG may test positive for DGP. This test is especially effective at diagnosing celiac disease in young children.

The American College of Gastroenterology recommends performing both DGP IgG testing and anti-tTG IgG testing for any patients with low IgA levels.

There are additional auto-antibody tests that are less commonly used to diagnose celiac disorder. These include:

This test can provide clarification if initial test results are inconclusive. EMA tests are difficult to perform when compared with anti-tTG tests.

ARA testing is surpassed by all the above tests for specificity and sensitivity. Thus, it is rarely ordered today.

As noted above, a celiac disorder diagnosis is generally confirmed by performing a biopsy on the small intestine. This can directly detect any damage to the intestinal villi. See the article on Histopathology for more information on biopsies.

There are genetic tests that can detect markers associated with celiac disease, but these are not used routinely. The key markers for celiac disease are the Human Leukocyte Antigen (HLA) markers DQ2 and DQ8. Genetic testing may be ordered for patients whose other test results are inconclusive and for screening family members in high-risk categories.

Genetic tests cannot make a conclusive diagnosis of celiac disease. The markers mentioned above are carried by roughly 30 percent of the general population, most of whom do not have the condition. Negative genetic results are useful, though, because they can rule out celiac disorder for individuals with inconclusive results on other tests (including biopsies).

Additional tests may be used to evaluate the extent of the disease and the patient’s symptoms. Examples include:

  • Stool fat — to evaluate nutrient absorption problems