Allergies Diagnosis and Testing

Allergy Diagnosis and Testing
Symptoms of allergic diseases can certainly give strong hints that a person is indeed suffering from allergies. However, in most cases, various tests are required to confirm a diagnosis. Testing depends on the type of allergic disease in question.
Atopic Dermatitis
There is no laboratory test that can be used to diagnose atopic dermatitis. Instead, a physician must examine a patient and review the history of her symptoms.

There are three criteria that must be present in order to diagnose atopic dermatitis:

•Allergies — The person must have allergies (at least one positive skin test) and/or a family history of allergic diseases in close relatives. There may be rare cases in which a person has atopic dermatitis without evidence of allergies.

•Itching — The patient must have itching and scratching in order for the rash to occur. If the skin or areas of the rash do not itch or have not been scratched, then the person does not have atopic dermatitis.

Allergies

•Eczema — Eczema refers to the appearance of the rash in patients with atopic dermatitis; it also occurs in those with other skin diseases. The rash appears red, with small blisters or bumps. These may ooze or flake with further scratching. Over the long-term, the skin appears thickened and leathery.
In most cases, people with atopic dermatitis should have skin testing performed to aeroallergens (pollens, molds, pet dander and dust mite) as well as to common food allergens. Avoiding allergic triggers is an important step in the treatment of atopic dermatitis.

Food Allergies
The diagnosis of food allergies is made when typical symptoms occur after eating a specific food and a patient receives a positive result after undergoing an allergy test to the food in question. Testing for the allergic antibody is best accomplished with skin testing, although can be done with a blood test as well.
The blood test, called a RAST, is not quite as good of a test as skin testing, but it can be helpful in predicting if a person has outgrown a food allergy. This is especially true since, in many cases, the skin test can still be positive in children who have actually outgrown the food allergy.

If the diagnosis of food allergy is in question despite testing, an allergist may decide to perform an oral food challenge. This involves having a person eat increasing amounts of the suspect food, over many hours, under close medical supervision. Given the potential for life-threatening allergic reactions, this procedure should only be performed by a physician experienced in the diagnosis and treatment of allergic diseases.

Introduction to food allergies

Either food allergy or food intolerance affects nearly everyone at some point. When people have an unpleasant reaction to something they ate, they often think that they have an allergy to the food. Actually, however, only about 1% of adults and 3% of children have clinically proven true allergic reactions to food.

This difference between the prevalence of clinically proven food allergy and the public’s perception of the problem is due primarily to misinterpreting food intolerance or other adverse reactions to food as food allergy. Food allergy is an abnormal response to food that is triggered by a specific reaction in the immune system and expressed by certain, often characteristic, symptoms. Other kinds of reactions to foods that are not food allergies include food intolerances (such as lactose or milk intolerance), food poisoning, and toxic reactions. Food intolerance also is an abnormal response to food, and its symptoms can resemble those of food allergy. Food intolerance, however, is far more prevalent, occurs in a variety of diseases, and is triggered by several different mechanisms that are distinct from the immunological reaction responsible for food allergy.

People who have food allergies must identify and prevent them because, although usually mild and not severe, these reactions can cause devastating illness and, in rare instances, can be fatal.

How do allergic reactions to food occur?

The allergens in food are those components that are responsible for inciting an allergic reaction. They are proteins that usually resist the heat of cooking, the acid in the stomach, and the intestinal digestive enzymes. As a result, the allergens survive to cross the gastrointestinal lining, enter the bloodstream, and go to target organs, causing allergic reactions throughout the body. The mechanism of food allergy involves the immune system and heredity.

Immune system: An allergic reaction to food involves two components of the immune system. One component is a type of protein, an antibody called immunoglobulin E (IgE), which circulates through the blood. The other is the mast cell, a specialized cell that is found in all tissues of the body. The mast cell is especially common, however, in areas of the body that are typical sites of allergic reactions, including the nose and throat, lungs, skin, and gastrointestinal tract.

Heredity: The tendency of an individual to produce IgE against something seemingly as innocuous as food appears to be inherited. Generally, people with allergies come from families in which allergies are common — not necessarily to food but perhaps allergies to pollen, fur, feathers, or drugs. Thus, a person with two allergic parents is more likely to develop food allergies than someone with one allergic parent.

Mechanism: Food allergy is a hypersensitivity reaction, meaning that before an allergic reaction to an allergen in food can occur, a person needs to have been exposed previously, that is, sensitized, to the food. At the initial exposure, the allergen stimulates lymphocytes (specialized white blood cells) to produce the IgE antibody that is specific for the allergen. This IgE then is released and attaches to the surface of the mast cells in different tissues of the body. The next time the person eats that food, its allergen hones in on the specific IgE antibody on the surface of the mast cells and prompts the cells to release chemicals such as histamine. Depending upon the tissue in which they are released, these chemicals cause the various symptoms of food allergy.

Allergies: Dubious Diagnosis and Treatment (Stephen Barrett, M.D.)

Many dubious practitioners claim that food allergies may be responsible for virtually any symptom a person can have. In support of this claim—which is false—they administer various tests purported to identify offending foods. Claims of this type may seem credible because about 25% of people think they are allergic to foods. However, scientific studies have found that only about 6% of children and 1-2% of adults actually have a food allergy, and most people with food allergies are allergic to less than four foods [1].

Cytotoxic Testing
The most notorious such test was cytotoxic testing, which was promoted during the early 1980s by storefront clinics, laboratories, nutrition consultants, chiropractors, and medical doctors. Advocates claimed it could determine sensitivity to food, which they blamed for asthma, arthritis, constipation, diarrhea, hypertension, obesity, stomach disorders, and many other conditions. However, controlled studies never demonstrated reliability, and some studies found it highly unreliable [2-5]. For example, one study found that white cells from allergic patients reacted no differently when exposed to substances known to produce symptoms than when exposed to substances to which the patients were not sensitive [6]. Government regulatory actions [7-10] and unfavorable publicity have almost driven cytotoxic testing from the health marketplace. But a few practitioners still perform it, and many use similar “food sensitivity” tests.

ELISA/ACT Testing
Another test claimed to locate “hidden allergies” is the ELISA/ACT, developed by Russell Jaffe, M.D., Ph.D., and performed by Serammune Physicians Lab (SPL), of Reston, Virginia, which Jaffe directs. According to an SPL brochure:

When we think of allergies, we immediately think of an allergy whose symptoms occur within minutes of ingesting a food or chemical. The symptoms include hives and itching. . . .

“Hidden” or “delayed” allergies are more difficult to identify because the onset of symptoms is delayed from 2 hours to 5 days and the symptoms range from physical pain to unexplained fatigue. Scientific estimates are that as much as 60% of all illness is due to hidden allergies [11].

The brochure states that any of the following may indicate the presence of hidden allergies: chronic headaches, migraines, difficulty sleeping, dizziness, runny or stuffy nose, postnasal drip, ringing in the ears, earaches, blurred vision, irregular or rapid heartbeat, asthma, nausea and vomiting, constipation, diarrhea, irritable bowel syndrome, hives, skin rashes (psoriasis, eczema), muscle aches, joint pain, arthritis, nervous tension, fatigue, depression, mental dullness, and difficulty in getting your work done.

The ELISA/ACT is performed by culturing the patient’s lymphocytes and seeing how they react to up to 300 foods, minerals, preservatives, and other environmental substances. After the test is completed, the practitioner (typically a chiropractor) recommends dietary modification and supplements. SPL maintains a referral list of practitioners who perform the test and suppliers who can provide “special combinations of the suggested supplements to reduce the number of ‘pills’ you may have to take.” In 1994, the complete (300-item) profile plus interpretation cost $695.

Although the ELISA/ACT test can assess the levels of certain immune responses, these are not necessarily related to allergy and have nothing whatsoever to do with a person’s need for supplements. Moreover, many of the symptoms listed in SPL’s brochure are unrelated to allergy and are not appropriately treated with supplement products. [Note: This test should not be confused with the ELISA test, which is a standard test for certain infectious diseases.]

Other Dubious Tests
In addition to cytotoxic testing and ELISA/ACT, the following procedures are not valid for managing food allergies:

ALCAT testing, which is said to measure how blood cells react to foods “under conditions designed to mimic what happens when the foods are consumed in real life.” [12]
NuTron testing, which supposedly measures the “reactivity” of white blood cells to food and other substances, is used design a diet that eliminates foods that cause white cell “activation.” Proponents claim that the diet can improve overweight and many other conditions “caused by the release of inflammatory chemicals from the activated white cells.”

The LEAP Program, in which the Mediator Release Test (MRT) is used to identify “delayed food allergies” and treatment involves dietary manipulation and possibly supplements and/or herbs.
Provocative testing, in which substances are injected under the skin in increasing doses until symptoms are reported
Sublingual testing, in which suspected foods are placed under the tongue
Neutralization, in which progressively smaller doses of substances are administered until the patient no longer reacts
Other food immune complex and IgG tests, which assess immune reactions that are common but not necessarily related to allergy
Desensitization, in which progressively larger doses of a food are injected. While desensitization may work for hay fever and other allergies related to inhaled substances, it is worthless for foods and can be dangerous.
Applied kinesiology, in which the patient’s arm strength is tested after test substances are placed in the patient’s mouth or hand.

Nambudripad’s Allergy Elimination Technique (NAET), based on the notion that allergies are caused by “energy blockage” that can be diagnosed with muscle-testing and permanently cured with acupressure and/or acupuncture treatments.

Electrodermal skin testing, in which a computerized galvanometer is used to detect supposed “energy imbalances.” In 1999, the British Advertising Standards Authority reviewed a pamphlet which alleged that a Bio Resonance Therapy device could help people suffering from headaches, overweight, tiredness, bloating, irritable bowel syndrome, skin rashes, arthritis, and premenstrual tension. In May 1999, after reviewing a manual and other information about the device, the Authority concluded that the claims were unsubstantiated [13].

Proper Testing
The correct way to assess a suspected food allergy or intolerance is to begin with a careful record of food intake and symptoms over a period of several weeks. Symptoms such as swollen lips or eyes, hives, or skin rash may be allergy-related, particularly if they occur within a few minutes (up to two hours) after eating. Diarrhea may be related to a food intolerance. Vague symptoms such as dizziness, weakness, or fatigue are not food-related. The history-taking procedure should note the suspected foods, the amounts consumed, the length of time between ingestion and symptoms, whether there is a consistent pattern of symptoms after the food is consumed, and several other factors. Although nearly any food can cause an allergic reaction, a few foods account for about 90% of reactions. Among adults these foods are peanuts, nuts, fish, and shellfish. Among children, they are egg, milk, peanuts, soy, and wheat [14].

If significant symptoms occur, the next step should be to see whether avoiding suspected foods for several weeks prevents possible allergy-related symptoms from recurring. If so, the suspected foods could be reintroduced one at a time to see whether symptoms can be reproduced. However, if the symptoms include hives, vomiting, swollen throat, wheezing, or other difficulty in breathing, continued self-testing could be dangerous, so an allergist should be consulted.

Proper medical evaluation—done best by an allergist—will include careful review of your history and skin testing with food extracts (using a prick or puncture technique) to see whether an allergic mechanism is involved in your symptoms. In cases where skin testing might be dangerous, a radioactive allergy sensitivity test (RAST) may be appropriate. The RAST is a laboratory test in which the technician mixes a sample of the patient’s blood with various food extracts to see whether antibodies to food proteins are present in the blood. It is not as reliable as skin testing and is more expensive. A negative prick or RAST test indicates a low probability of allergy to the test substance. Positive tests, however, have much less predictive value [1].

The only sure way to diagnose an allergy to a suspected food, food coloring, or other additive is challenge testing in which the patient ingests either the suspected food or a placebo [14]. This may be appropriate if the patient’s history suggests a food allergy but the skin or RAST tests are negative. Because dangerous reactions can occur, challenge testing should be done in a hospital or office that is specially equipped for that purpose.

Allergies Diagnosis & Tests

The history of your symptoms is important in diagnosing all allergies, including whether the symptoms vary according to time of day, season, exposure to pets and other potential allergens, and diet changes. Severe reactions often develop very quickly after exposure, such as eating culprit nuts or getting stung.

Allergy testing may be required to determine if your symptoms are an actual allergy or caused by other problems. For example, eating contaminated food (food poisoning) may cause symptoms that resemble food allergies. Some medications (such as aspirin, ampicillin, and others) can produce non-allergic reactions, including rashes, that resemble drug allergies but are not true allergies.

Tests that may reveal the specific allergens include:

Skin testing — the most common method of allergy testing. This may include intradermal, scratch, patch, or other tests. Skin testing may even be an option for young children and infants, depending on the circumstances.
Blood test — also called RAST (radioallergosorbent), this measures the levels of allergy antibody, IgE, produced when your blood is mixed with a series of allergens in a laboratory. If you are allergic to a substance, the IgE levels may increase in the blood sample. The blood test may be used if you have existing skin problems like eczema, if you’re on medications that are long-acting or you cannot stop taking, if you have a history of anaphylaxis, or if you prefer not to have a skin test.

“Use” or “elimination” tests — suspected items are eliminated and/or introduced while the person is observed for response to the substance. This is often used to check for food or medication allergies.
Eyelid — Occasionally, the suspected allergen is dissolved and dropped onto the lining of the lower eyelid (conjunctiva) as a means of testing for allergies. (This test should only be done by a physician, never the patient, since it can be harmful if done improperly.)
Reaction to physical stimuli — application of heat, cold, or other stimulation, and then look for an allergic response.
Other tests that may reveal allergies include:

Antibody/immunoglobulin (particularly IgE) levels — when these are elevated, it indicates a “primed” immune system.
CBC — may reveal an increase in eosinophils.
Complement levels — may be abnormal.

*************

Diagnostic tests for Allergies:Respiratory allergies can be difficult to diagnose and thus may be both over-diagnosed and under-diagnosed at different times. A full evaluation by a medical professional, primary care physician or nurse practitioner, pediatrician, in conjunction with an allergist and asthma specialist, as indicated, is necessary to properly diagnose respiratory allergies and the allergens that cause them.

The most common form of testing for respiratory allergies is skin testing, most often the “scratch test”. This test includes putting a small amount of a possible allergen on the skin of the arm or back, then scratching or pricking the skin so the substance inters the body. The patient is then observed for a reaction to that substance, such as redness or swelling. Multiple possible allergens can be tested at one time.