Blood-Tests

If you have been diagnosed with celiac disease, you know how long it can take. Doctors are always looking for an easier and faster way to make the diagnosis.

Researchers are searching for the perfect blood test to detect celiac disease. This test, which has not been found yet, would only be positive in people with celiac disease, and only negative in people without it. While many of the blood tests used to screen for celiac disease have been in use for as long as 20 years, the earlier tests were not good enough at finding patients with CD.

The blood tests currently in use are better than older tests, but definitely not perfect. Most people now have been screened with the blood tests called EMA (which stands for endomysial antibodies) and anti-tTG (which stands for antibodies to tissue transglutaminase). There are newer blood analyses that may be somewhat better at finding people with CD.

These newer tests are already in use in some places. One is based on finding antibodies to parts of gluten called gliadins. The gliadins have already been changed in the body of the person with celiac disease, and the blood test looks for antibodies to the altered gliadins, which are called deamidated gliadin-related peptides (DGPs).

If you have been diagnosed with CD, you also may have had your immunoglobulin levels checked. Immunoglobulins are the substances your body makes to attack what it believes are dangerous chemicals or germs. In CD, they are reacting to parts of gluten as if it were dangerous.

There is more than one type of immunoglobulin. Most of the time, people are tested for immunoglobulin A antibodies. Some of the newer tests automatically check for immunoglobulin G antibodies at the same time. This bypasses a step in which people with negative blood tests have their immunoglobulin A levels checked before other tests.

The newer tests look for both types of antibodies (IgA and IgG) to the DGPs. One is called “DGP Dual.” Another test, called tTG/DGP Screen looks for IgA and IgG antibodies to gliadin as well as tissue transglutaminase.

Both of these tests have two advantages. Firstly, they can pick up a positive test even in a person who does not make IgA, which may be the case in around 5% of people with CD. Secondly, they are looking for antibodies to a different substance, DGPs, which may be found more commonly than the other antibodies in CD.

Which of these tests is best for celiac disease screening and diagnosis is the subject of much research. An example is a study in 2010, which looked at a group of people who had clinical symptoms of CD with negative standard tests, had dermatitis herpetiformis, or had celiac disease with positive standard tests. All of these patients had blood tested using the DGP Dual test and the tTG/DGP Screen as described above.

All the patients who were positive to the commonly used tests were also positive in the anti-DGP tests. Six of the patients who were negative in regards to the usual test were positive in the tTG/DGP screen. Five people in the same group were positive when tested by the anti-DGP Dual. These were small numbers of patients.

Since all of the patients who had positive older tests were positive with the new tests, the new tests would not miss patients diagnosed with the older tests.

While the research demonstrated that using the new tests would pick up a small percentage of cases of CD with normal results on the commonly used serologic tests, and they can be used in people with or without IgA deficiency, the tests are not good enough to replace biopsies. They are useful screening tests in general and also when IgA deficiency is found or suspected.

These two new tests may replace EMA and a-tTG in many instances, and may mean a quicker diagnosis for a small percentage of patients. They are successful in shortening some of the time to diagnosis. However, these tests will unfortunately not revolutionize the diagnosis of celiac disease.

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Reference:
Sugai E, Hwang HJ , Vazquez H, et al. New Serology Assays Can Detect Gluten Sensitivity among Enteropathy Patients Seronegative for Anti–Tissue Transglutaminase. Clinical Chemistry 2010;56(4):661–665.

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