How to Read a Food Allergy Profile

What Yous Need to Know About Nutrient Allergy Testing

by David Stukus, MD

Whenever I run into with families for the start time and ask the parents whether their child has any food allergies, I ofttimes hear the post-obit reply: "I don't know, he/she's never been tested". This always presents a wonderful opportunity to discuss the role of diagnostic testing for nutrient allergies, equally I'd like to practice in this forum.

Before we go any further, I'd like to ascertain some common terms that you lot may encounter when reading nigh or discussing food allergies:

1. Allergy – This is an allowed response to a detail food. Symptoms should occur every time that nutrient is ingested.  These allowed system changes fall into two categories: Immunoglobulin E (IgE) mediated and non-IgE-mediated.
2. Sensitization – This is the detection of specific immunoglobulin E (IgE) through skin prick or claret testing towards a specific food, but without the development of symptoms after that nutrient is ingested. In other words, a positive allergy test effect to a food that your child has eaten without any problems, or has never eaten.
3. IgE mediated hypersensitivity/allergy – Commonly referred to as "food allergy", in which IgE antibody specific for a food is formed and attaches to the allergy cells throughout the body. Whenever that nutrient is ingested, it causes immediate onset symptoms, usually within minutes or up to 3 hours later on ingestion. Typical symptoms include hives, swelling, itchy/h2o nose and optics, difficulty animate/swallowing, vomiting, and tin can progress to loss of consciousness. Pare prick or claret specific IgE testing is very likely to be positive for that food.
4. Anaphylaxis – Rapid onset, progressive, astringent symptoms involving more than 1 organ system that tin occur with IgE mediated nutrient allergy.
5. Non-IgE mediated reaction – This is an immunologically mediated, typically delayed-onset reaction to a particular food. This is mediated past other parts of the immune system separate from IgE, specifically T-cells. These symptoms are not immediate in onset and tin can occur hours to days later ingestion. Anaphylaxis is non part of this response and most symptoms involve the alimentary canal, with vomiting, upset breadbasket, diarrhea, or blood in the stool. Skin prick or claret specific IgE testing is negative.
6. Sensitivity or intolerance – This is a non-immunologic response to a sure food or foods. Symptoms occur when that food is consumed, merely may be variable over time. This also most often includes gastrointestinal symptoms and does not include symptoms observed with IgE mediated reactions. Skin prick or blood specific IgE testing is negative.

When trying to determine whether a child has a food allergy, in that location are many steps involved. Beginning, the most of import part is taking a careful history of suspected foods, the timing and types of symptoms that occur, and any treatment that has earlier used to help make symptoms better. If the history is consistent with an IgE mediated allergy, then testing is often pursued. However, a good rule of thumb to remember is, if your child can eat a food without developing any symptoms, then they are unlikely to be allergic to that food. Why is that? Because the best test is actual ingestion of the food. In regards to IgE mediated allergy, y'all're almost always going to know if a sure nutrient makes your child sick, and there are no 'hidden' food allergies. In many circumstances, the history is more consequent with not-IgE mediated symptoms or intolerance and skin prick or specific IgE testing is not helpful, necessary, or indicated. This is the signal when many families ask, "Why don't nosotros just do the allergy tests to find out for sure?" If only it were and so like shooting fish in a barrel.

Before we hash out any further, I'd like to mention something that is very important to keep in heed when discussing food allergy testing. A positive test issue for food allergy is non, in and of itself, diagnostic for food allergy. These tests are best utilized to help confirm a suspicious history for IgE mediated food allergies. They take high rates of falsely elevated and meaningless results and are non useful screening tools. Some commercial laboratories offer convenient "screening panels", in which many different foods are included. These are rarely utilized by Allergists/Immunologists, but more than ordinarily ordered by primary care providers. This often results in falsely elevated results, along with diagnostic confusion and unnecessary dietary elimination. Ultimately, your child may have nutrient(southward) removed from their diet for no reason other than a meaningless positive examination result. This may and so lead to anxiety, family unit hardship due to food abstention, and potentially nutritional deficiencies.

There are iii chief ways to test for IgE mediated food allergy:

1. Skin Prick Testing (SPT): This involves placing a driblet of allergen onto the surface of the skin, and and then pricking through it to introduce the allergen into the top layer of the peel. If specific IgE antibiotic towards that allergen is nowadays and attached to the allergy cells, then an itchy bump and surrounding redness (wheal/flare) should develop within fifteen minutes. These tests take a high negative predictive value (when a examination yields a negative outcome, it is very likely to be right), but a low positive predictive value (when a examination yields a positive result, information technology is less likely to exist correct) which can result in fake positive test results. Thus, it is not a proficient screening tool but is a very reliable test to ostend a history that is consistent with an IgE mediated food allergy.

   

   
   In guild to go accurate results, all antihistamines should be discontinued for 5-seven days earlier testing. A common myth is that skin prick testing is not reliable in young infants and children. Actually, skin prick testing to foods is reliable at any age if y'all have a history of IgE mediated food allergy. Tests may exist negative in young children when they are performed for other conditions such as non-IgE mediated formula or food intolerance.
2. Specific IgE (sIgE) Blood Testing (previously and commonly referred to as RAST or ImmunoCAP testing): This test measures levels of specific IgE directed towards foods in the blood. The range, depending upon the laboratory technique, tin can go from 0.ten kU/50 to 100 kU/Fifty. This also has a very high negative predictive value only a low positive predictive value. Mildly elevated results are often encountered, especially in children who have other types of allergic weather condition such equally eczema, asthma, and allergic rhinitis. The predictive values for likelihood of an allergy existence present differ with every food, but in general, the college the level, the more likely that an IgE mediated allergy is present. This is likewise a very poor screening test due to the high rates of falsely elevated and meaningless results.

   I've met many families whose children take been 'screened for food allergies' in the setting of eczema or other conditions and the written report lists every food that was tested as being 'high', as their cutoff for reporting this is often fix very low, at levels that are unremarkably meaningless. This leads to diagnostic confusion and unnecessary dietary elimination. In add-on, many laboratories will report an arbitrary class designation (a created value that is assigned to a upshot that has no meaning or scientific basis), along with the actual level of specific IgE obtained. This is of no clinical use and also does not aid decide whether food allergy is nowadays.  It is also commonly misunderstood that higher blood examination levels indicate increased "severity". Unfortunately at that place is no examination that can determine severity. Individuals with higher claret (or skin) tests are at no more increased risk of anaphylaxis than someone with minimally positive tests.

   TAKE Notation: "Form Levels" are meaningless.

   
   
3. Physician Supervised Oral Food Claiming (ordinarily referred to as IOFC on KFA):This entails consumption of gradually increasing amounts of the suspected food allergen while being supervised past a physician, usually an Allergist. If no symptoms develop that are consistent with an IgE mediated food allergy (hives, swelling, anaphylaxis), so it makes the presence of IgE directed toward that food unlikely. This is often considered the gold standard for food allergy testing, and can exist considered a good way to 'rule out' food allergy or determine if a previously diagnosed nutrient allergy has gone away. This is time consuming every bit near challenges take four-eight hours to complete but can be a very reliable exam.

   Accept NOTE: The gold standard for diagnosing a food allergy is through a doctor-supervised oral food challenge.

Equally y'all can see, performing diagnostic testing for food allergies can be very complicated and requires careful consideration nearly what tests to gild and how to interpret them. There are very few indications to perform an all-encompassing 'screening panel' for food allergies. However, obtaining a careful history of what specific foods cause symptoms and and so using the type of symptoms can be a helpful guide to determine whether specific IgE testing is worth pursuing, or to get in a different direction.

Lastly, a give-and-take of circumspection regarding other commonly used techniques (often utilized by non-board certified Allergists/Immunologists) that you may encounter. Specific IgG blood testing for foods, muscle provocation testing, acupuncture, hair/urine assay, and applied kinesiology are not validated, standardized, or FDA approved tests for the diagnosis of food allergy or food intolerance. Use of these tests is not recommended by the American Academy of Asthma, Allergy, and Immunology, or supported by the Guidelines for the Diagnosis and Management of Food Allergy, published in 2010 (Journal of Allergy and Clinical Immunology, 126(half dozen); supplement S1-56).

References

Guidelines for the Diagnosis and Management of Food Allergy, published in 2010(Journal of Allergy and Clinical Immunology, 126(six); supplement S1-56).

Dr. David Stukus is an Assistant Professor of Pediatrics in the Section of Allergy/Immunology at Nationwide Children'south Hospital in Columbus, Ohio. In add-on to his interest in caring for families with food allergies and other allergic conditions, he also serves as the Manager of the Complex Asthma Dispensary.  He currently serves every bit the chair of the Medical Informational Team for Kids With Nutrient Allergies and sits on the Board of Directors for the Asthma and Allergy Foundation of America. He previously completed his residency at Nationwide Children'southward Hospital and his fellowship at the Cleveland Clinic. You can follow him on Twitter @AllergyKidsDoc.

Medical review Oct 2012 and Apr 2014.

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Source: https://www.kidswithfoodallergies.org/food-allergy-test-diagnosis-skin-prick-blood.aspx

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