While the media, restaurants and grocery stores are inundated by the hype surrounding the gluten-free diet, at the core of this matter lies several serious and difficult-to-diagnose forms of gluten intolerance. And despite what you might have heard (or even been told by your doctor), testing for a gluten intolerance is not a simple cut and dry matter.
Use the following lesson index to skip straight to any section:
- What Is Gluten?
- How Many Forms of Gluten Intolerance Exist?
- Understanding Specificity and Sensitivity In Blood Tests
- Clinical Gluten Intolerance Tests
- Why Doctors Want You Tested Before You Go Gluten Free
- Blood Panels That Might Suggest A Problem
- Genetic Testing For Celiac Disease
- Celiac Disease Is More Common Than Most Doctors Realize
- Allergy Testing
- What You Need to Know
- Take The Quiz
What Is Gluten?
Gluten is a protein composite found in the triticae family of grassy grains; the most common and potent forms of gluten are found in wheat, barley and rye. It provides dough unique stretchiness and strength, and gives baked goods form and texture.
Even if you avoid these grains, this pesky protein composite is added to so many products that it can be very difficult to completely remove it from your diet.
To better understand gluten and to learn just how pervasive it is in the western diet, see the following lesson: What Is Gluten?
How Many Forms of Gluten Intolerance Exist?
This surprises some people (even some doctors, unfortunately), but there is more to gluten intolerance than celiac disease. While it is still considered the most serious medical condition among them, celiac disease is only one of several signficant medical conditions triggered by the consumption of this troublesome protein composite.
- Celiac Disease
- Non-Celiac Gluten Sensitivity (NCGS)
- Wheat Allergy
- Dermatitis Herpetiformis
- Gluten Ataxia
Along with gluten ataxia, a growing number of gluten-sensitive idiopathic neuropathies are being diagnosed.
Unfortunately, each of these conditions require a different means for diagnosis and with two of them, NCGS and gluten ataxia, doctors and researchers haven’t yet agreed upon a consistent and accurate way to perform diagnosis.
In addition, one form of gluten intolerance, dermatitis herpetiformis, requires a skin biopsy, not blood work. Also, doctors and researchers haven’t yet agreed on how to identify a non-celiac gluten sensitivity in a consistent and accurate manner, other than to rely on a diagnosis by deduction.
In other words, if a gluten challenge reveals a problem with gluten but the patient tests negative for both celiac disease and a wheat allergy, then the patient will be diagnosed as non-celiac gluten sensitive (NCGS).
Understanding Specificity and Sensitivity In Blood Tests
Different conditions rely on tests with different degrees of specificity and sensitivity. These terms are important to understand:
Specificity is defined by what possible conditions can cause a positive result for a test. If only one single condition or disease can cause a positive result, than that test is considered 100% specific to that condition.
But if more than one condition might change the antibodies measured by the test, than it is not a 100% specific test.
Sensitivity is defined by how often a test identifies people with a condition. Some tests will only show a positive result for 90% of people who take the test. So that test would be considered 90% sensitive.
Unfortunately, it isn’t very common for tests to be 100% specific and 100% sensitive. This is why most blood tests involve a combination of tests. Sometimes the result is determined by both a combination of tests and the doctors interpretation of your overall medical profile.
Clinical Gluten Intolerance Tests
In the case of celiac disease, we now have 4 different established blood tests to help identify it:
- Deamidated Gliadin Peptides (DGP)
- IgA and IgG Antigliadin Antibodies (AGA)
- IgA Endomysial Antibodies (EMA)
- tgG Tissue Transglutaminase Antibodies (tTG)
In addition, the following test is almost always ordered to identify patients whose test results will be skewed due to an IgA deficiency:
Total IgA antibodies (To measure for IgA Deficiency)
None of these are 100% specific or 100% sensitive, which is why a doctor experienced in diagnosing celiac disease and a non-celiac gluten sensitivity will order several of these tests.
Since none of these can give you a 100% accurate answer, your doctor will consider your lab results and determine if you need an endoscopy with biopsy. Doctors often use more than the lab results to make this decision: your symptoms, medical history and family history are all taken into consideration.
An intestinal biopsy is considered, by most doctors and researchers, to be the only definitive test for celiac disease. It is often referred to as the “gold standard” for celiac disease diagnosis.
If your doctor decides to do a blood panel for celiac disease, try to make sure he or she uses the most recent and accurate tests: Deamidated Gliadin Peptides and IgA Endomysial Antibodies.
In addition, the Total IgA Antibody test should always be taken to determine if you are IgA deficient. If you are IgA deficient, they will need to read the results of your other tests differently (and in some cases the tests will not provide useful results).
If your total IgA is low enough, your doctor may run a IgG tissue transglutaminase antibody test instead.
Another test popular among laymen online is the Fecal Anti-Gliadin Antibodies test (fAGA), most prominently conducted and promoted by the Enterolab. However, corroborating research in peer review journals hasn’t been done yet. Anecdotal evidence among my readers suggests a high rate of success with this test, but again note that you may test negative if you’ve already subscribed to a strict gluten-free diet. Also, most doctors and researchers I’ve consulted don’t believe this test is either specific or sensitive enough to be relied upon to diagnose either celiac disease or non-celiac gluten sensitivity.
Why Doctors Want You Tested Before You Go Gluten Free
A gluten-free diet can reduce the biomarkers doctors use to confirm the presence of celiac disease, making a complete diagnosis very difficult. Doctors don’t like to have an inconclusive diagnosis because celiac disease is a serious medical condition that should be in your official medical profile.
Basically, once you remove gluten from your diet, your body produces less of the harmful antibodies triggered by gluten and the villi along the wall of your small intestine begin to heal. If your villi are healthy and you don’t have raised antibodies in your blood, you may test negative for celiac disease. So if you take steps to eliminate a gluten intolerance on your own, you may also make it difficult to have your condition accurately diagnosed.
Because patients are understandably wary about eating food they’re sure is hurting them, doctors and researchers are trying to make testing more sensitive so that a gluten challenge can be shorter and less intimidating.
Blood Panels That Might Suggest A Problem
The following tests are often conducted by thorough doctors when evaluating patients for a non-celiac gluten sensitivity, a gluten intolerance or a verified case of celiac disease:
- Stool Fat test, to determine malabsorption level (test for Steatorrhea).
- Complete Blood count (CBC), to determine anemia.
- Erythrocyte Sedimentation Rate (ESR) to look for inflammation.
- C-Reactive Protein (CRP) to further watch for chronic inflammation.
- Vitamins A, D, E and K (the fat-soluble vitamins) to check for vitamin deficiency relating to malabsorption in the proximal small intestine.
- Comprehensive Metabolic Panel (CMP) to analyze protein, calcium and electrolyte levels as well as to check liver and kidney functions.
I’ve also had readers inform me that they’ve had doctors test and confirm a Non-Celiac Gluten Sensitivity (NCGS) with the gliadin IgG non-deamidated antibody test. I think many doctors and researchers would consider this too simple and narrow, but at least some anecdotal evidence suggests otherwise.
Genetic Testing For Celiac Disease
The most established genetic test is specific to celiac disease and not necessarily for a wheat allergy, a non-celiac gluten sensitivity or a broader intolerance. But it can help either verify the presence of celiac disease or identify people who may be predisposed to developing celiac disease. Because it can be done in a non-invasive manner (a saliva swab is often enough), this celiac disease genetic test is often done for at-risk children.
The test looks for the HLA-DQ2 and HLA-DQ8 genes. If one or both genes are present and the patient has a family history of digestive concerns, the individual is at a greater risk of developing celiac disease at some point in his or her life.
Please note, however, that it is still possible to have these genes and not develop celiac disease. In fact, around 35% of the general population has these genes while around 1% of the population has celiac disease. That means millions of people have the so-called celiac gene but do not have celiac disease.
So this test is usually either to take preliminary steps in identifying and helping at-risk individuals (people who have celiac disease in their immediate family) or to help confirm a diagnosis begun with some of the tests listed earlier in this lesson.
Celiac Disease Is More Common Than Most Doctors Realize
Many doctors still consider celiac disease to be relatively rare (although current gluten intolerance statistics may suggest otherwise), so if your doctor doesn’t bring up the possibility of celiac disease, you need to speak up and be your own health advocate.
According to recent research published in the BMC Journal, “The mean delay to diagnosis from the first symptoms was 9.7 years, and from the first doctor visit it was 5.8 years.” What this means is that, on average, it is taking doctors nearly six years to properly diagnose celiac disease after a patient first visits his or her doctor complaining about symptoms. Right now, millions of people all over the world are walking around with celiac disease but don’t realize it.
In addition, please note that just because you test negative for celiac disease does not mean with certainty that you still do not have some form of gluten intolerance. It also does not preclude the possibility of a wheat allergy. For more on these distinctions, please read gluten allergy symptoms.
Note that as of March 2011, a gluten sensitivity may exist as its own clinical entity, separate from celiac disease. Many doctors and researchers currently believe the only way to distinguish this form of gluten intolerance from celiac disease is to do an intestinal biopsy. This new condition has become widely known as NCGS, for non-celiac gluten sensitive.
This is usually a skin prick test, which allows a doctor to test for a variety of food and other allergies at once. If the skin prick test comes back positive for a wheat allergy, an elimination diet is the next step. If it does not come back positive, more testing is done to rule out other illnesses or conditions that could cause similar symptoms.
An allergy is a type 1 hypersensitivity, not an autoimmune disease, so it is possible to have a wheat allergy but not have celiac disease, and vice versa.
What You Need to Know
Diagnosing celiac disease is not simple. To assume a single blood test will accurately diagnose your condition is to greatly underestimate the process.
In addition, you can test negative for celiac disease but still have one or more of several different forms of gluten intolerance, including:
- Non-Celiac Gluten Sensitivity
- Wheat Allergy
- Dermatitis Herpetiformis
- Gluten Ataxia
Each of these conditions require a different mode of diagnosis. Dermatitis herpetiformis requires a skin biopsy, not blood work.
An endoscopy with biopsy is still considered the gold standard for diagnosing celiac disease.
The most recent and accurate blood tests available are the tests for Deamidated Gliadin Peptides and IgA Endomysial Antibodies, so if your doctor decides to do blood work, make sure these are done.
Take The Quiz!
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