What Food Allergy Testing Can Tell Doctors

A food allergy is the body's immune response to a particular food. Children who have a food allergy should experience symptoms each time they eat the food. Food sensitivity or intolerance can cause symptoms as well, although the onset generally is delayed rather than immediate. Symptoms also can change over time.

While food intolerance can cause symptoms to certain foods similar to a food allergy, food intolerance is usually less serious than an allergic reaction. Your child's doctor or an allergist may need to perform screening tests that look for certain antibodies in the blood. If the tests rule out a food allergy as the cause of your child's symptoms, a food elimination diet usually is a more reliable method for identifying food intolerance.

Food Sensitivity/Intolerance

Food sensitivity or intolerance differs from a food allergy. While eating a certain food may cause symptoms, it's not an allergic response. With food sensitivity or intolerance, gastrointestinal symptoms often occur; however, your child may not experience other symptoms, such as itchy eyes and runny nose, hives, rashes, swelling, lowered blood pressure, or difficulty breathing, that occur with a food allergy. Food intolerance typically isn't life threatening. On the other hand, a food allergy can cause death if your child has a severe reaction to a food allergen and goes into anaphylactic shock.

Antibody tests used to screen for food allergies produce negative results when food sensitivity or intolerance is the cause of symptoms. When there is no allergic antibody present, common causes of food intolerance your child's doctor may investigate include irritable bowel syndrome, celiac disease, lactose intolerance, or sensitivity to food additives.

Standard Food Allergy Tests

  • Specific IgE Blood Testing – Although the test detects IgE antibody in the blood, a drawback is it may measure elevated levels if your child has another allergic condition such as asthma, eczema, or allergic rhinitis (hay fever). In that case, many of the foods for which the doctor screens for allergies may produce high results when a food allergy is not necessarily present. However, the higher the level of IgE antibody to a specific food, the more likely that your child has an allergy to that food.
  • Skin Prick Testing (also known as a scratch test) – The skin becomes red and an itchy bump develops when a suspected allergen is introduced just beneath the top layer of the skin. But because the test can produce false positive results, it's not always a reliable screening tool. While a doctor may use the test as a means for confirming a history of food allergy, a negative test result is usually accurate. Conversely, false positives can occur when the test shows a reaction to foods that share similar proteins when only a specific protein is the allergen. It's also necessary to discontinue the use of antihistamines for several days prior to testing to get more accurate results.
  • Physician Supervised Oral Food Challenge (elimination diet) – Because it's important for children not to have their health or development compromised by nutritional deficiencies, eliminating foods from the diet should be conducted under careful supervision by a doctor or registered dietitian. Before the doctor begins screening for a food allergy, he or she needs to take a careful history of what foods your child eats when symptoms occur, as well as what types of symptoms occur.

Once a suspected food allergen is removed from your child's diet, it is then reintroduced in gradually increasing amounts. If no allergy symptoms develop, that particular food allergy is ruled out. Although the test is time-consuming, it tends to be more reliable at detecting an IgE mediated food allergy -- one in which antibodies for a particular food are present in the body. If your child suffers only gastrointestinal symptoms, such as constipation, diarrhea, or stomach pain, that disappear by avoiding certain foods or food groups, your child may have food intolerance. Visit http://www.entfpss.com for more information.

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