Testing Your Intestines

by Brooke on September 2, 2014

By:  Erica Meador MS, RDN, LDN

I’m happy to be writing for all of you again this week and giving you more information on how to navigate testing and diagnoses for food allergies and intolerances involving wheat and gluten.

Let’s start with wheat allergy.  There are three ways to test for wheat allergy: a skin test, a blood test, or a challenge test.  The blood testing (RAST test) is the most expensive, but carries least risk of allergic reaction.  Blood is drawn and tested in a lab for IgE antibodies (or allergy) to wheat.  Skin testing is most commonly used and can be done as a scratch test where plastic prongs are scraped along the skin (often the arm) and the allergen in liquid form is put onto the small area of scratched skin.  Another form of skin testing involves actually injecting a very small amount of the allergenic protein under the skin (often on arms or back).  In skin testing, someone that is wheat-allergic will get a welt like a bug bite on their skin where the wheat protein was placed.  

Celiac disease can be diagnosed by either a combination of blood tests and intestinal biopsy OR by skin biopsy if the patient has a skin rash that looks like dermatitis herpetiformes (specific to celiac).  The blood tests for celiac should include the following: Total IgA (because 2-5% of those with celiac and 0.5-1% of general population are IgA deficient), IgA-tTG, and sometimes DGLDN-IgA.  If the total IgA comes back low (meaning someone may have celiac but it won’t show up with the IgA blood tests, then tTG-IgG, and DGLDN-IgG are run, and sometimes an EMA blood test.  If blood tests come back positive then an intestinal biopsy is completed to confirm diagnosis since celiac disease results in the surface of the intestine looking mashed down and inflamed under a microscope. This involves going under anesthesia, getting an endoscopy (tube with camera down the throat) and several extremely small pieces of intestine are taken from the first section of the intestine past the stomach.  Genetic testing can also be completed, but that can’t confirm diagnosis because 40% percent of people have one of the genes for celiac, but only 1 in 133 actually has celiac!  One of the most crucial things to remember with celiac testing is that if you go gluten-free, you won’t have elevated antibodies anymore.  You MUST keep gluten in your diet for test results to be accurate.  The recommended time frame of chowing down on gluten before testing is two months, while consuming  at least two slices of bread daily.  This recommendation varies, but the 2/2 rule shows great results!

Irritable bowel syndrome is a diagnosis of exclusion.  For example, your doctor may say “well, you don’t have any other intestinal disease, so it must be irritable bowel.” In many cases, it is confirmed through resolution of symptoms with the removal of offending foods and the return of symptoms with reintroduction of those foods.  However, this can only happen if you have a doctor and medical team that understand IBS, food triggers, and how to conduct an elimination diet.  A correctly followed FODMAP diet results in resolution for 75% of people with suspected IBS, eliminating the following food components: fructans, galactans, lactose, excess fructose, and polyols.   Lactose and fructose malabsorption can actually be tested by your gastroenterologist via hydrogen and methane breath tests (drink a glass of lactose or fructose and huff into a machine every 15 minutes for 2 hours).  An elevation means that the bacteria in your intestines are eating the lactose or fructose and releasing methane and hydrogen rather than YOU digesting and absorbing lactose or fructose.

Non-celiac gluten sensitivity (NCGS) is poorly understood, and is at this time also a diagnosis of exclusion.  Many doctors do believe it exists, but they think the numbers are much lower than once thought.  The mechanism in the body is unknown and there are unfortunately no tests to determine if you have it!

The bottom line is that testing is very important.  Different foods are involved in each of these conditions (see table below).  Therefore, many of individuals may still be having symptoms because they need a correct diagnosis so they can pull the correct foods from their diets’.  Need more help?  Make an appointment with your gastroenterologist AND dietitian.  Good luck!


Wheat Allergy


Irritable Bowel Syndrome

Non-Celiac Gluten Sensitivity

Substance Causing Reaction: 




(Fructans are common)


Foods Implicated


Wheat, Barley, Rye, Oats

Fructans include:

Wheat, Barley, Rye, Onions, Garlic (as main offenders)

Wheat, Barley, Rye, Oats





Unknown, suspected to be low




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