Controversial Diagnostic Techniques

Just as there are controversial food allergy syndromes and treatments there are also controversial ways of diagnosing food allergies. One of these is cytotoxicity testing, in which food allergen is added to a patient's blood sample. A technician then examines the sample under the microscope to see if white cells in the blood "die." This technique has been evaluated in a number of studies and has not been found to effectively diagnose food allergy.

Another controversial approach is called sublingual or, if it is injected under the skin, subcutaneous provocative challenge. In this procedure, dilute food allergen is administered under the tongue of the person who may feel that his or her arthritis, for instance, is due to foods. The technician then asks the patient if the food allergen has aggravated the arthritis symptoms. In clinical studies, this procedure has not been shown to effectively diagnose food allergies.

An immune complex assay is sometimes done on patients suspected of having food allergies to see if there are complexes of certain antibodies bound to the food allergen in the bloodstream. It is said that these immune complexes correlate with food allergies. But the formation of such immune complexes is a normal offshoot of food digestion and everyone, if tested with a sensitive enough measurement, has them. To date, no one has conclusively shown that this test correlates with allergies to foods.

Another test is the IgG subclass assay, which looks specifically for certain kinds of IgG antibody. Again, there is no evidence that this diagnoses food allergy.

Controversial Treatments

Controversial treatments include putting a dilute solution of a particular food under the tongue about a half hour before the patient eats that food. This is an attempt to "neutralize" the subsequent exposure to the food that the patient believes is harmful. As the results of a well conducted clinical study show, this procedure is not effective in preventing an allergic reaction.

Summary

Food allergies are caused by immunologic reactions to foods. There actually are several discrete diseases under this category and a number of foods that can cause these problems.

A medical evaluation after one suspects a food allergy is the key to proper management. Treatment is basically avoidance of the other food(s) after they are identified. People with food allergies should become knowledgeable about allergies and how they are treated and should work with their physicians.

The National Institutes of Health supports research on food allergies through grants that it provides to research institutions throughout the world. Understanding the cause of an immune system dysfunction in allergy will ultimately lead to better methods of diagnosing, treating and preventing allergic diseases.

Questions and Answers

Q. Would you discuss what common substances are in both peanuts and other kinds of nuts? The response I often get when I tell people that I am severely allergic to both peanuts and nuts is that I cannot be because peanuts are legume, unlike nuts.

A. First of all, it is possible to be allergic to two distinct foods. It is interesting that both peanuts and nuts are concentrated sources of protein, which is probably one reason why reactions to both these foods are so frequent. But you can have cross reactions between tree nuts and peanuts, or you could develop allergies to both.

Q. I would like to ask about diet during pregnancy. I have heard some talk about avoiding certain foods during your last trimester.

A. There is no evidence that avoidance of foods in the last trimester can prevent food allergies. In fact, some experimental evidence suggest this is harmful.

Q. Would gross swelling of the lips be indicative of a food allergy?

A. Well, it can be, but you can also have something called idiopathic angioedema, which can cause swelling of the lips. This disorder is not caused by food allergies. If you have such a problem, talk it over with your doctor. If there is any chance that it might be a food allergy, the doctor can place you on an elemental diet for 10 days. If the problem does not go away, you have ruled out food allergy.

Q. Is intolerance a disease entity?

A. Food intolerance is not a distinct entity. It is a term used to cover any adverse reaction to a food that doesn't have an immunologic basis.

Q. I have a 14-year old daughter who has developed chronic hives in the past nine months. She has swelling and hives on the bottom of her feet to the point where she cannot walk; her fingers swell and she cannot write. She has been skin tested for food allergies, and it was negative. We are going through the elimination diet process now and seeing some improvement, but not a whole lot. The only thing that controls it is prednisone. What would you suggest as the next step?

A. Sometimes there is a non-specific improvement as you manipulate the diet. But chronic hives and angioedema, especially of that duration, are almost never due to food allergies. Unfortunately, no cause is usually found. There is hope that they will resolve with time. I'd advise you to limit the use of steroids because steroids can do more damage than if you just use antihistamines.

Q. Is there any hope of better management of lactose intolerance than chewing tablets that help dissolve lactose during the meal?

A. Probably not, other than avoidance of foods that have lactose.

Q. What is the best way to diagnose lactose deficiency?

A. There are a couple of test that involve ingesting a specific amount of lactose and then measuring the body's response. Such blood tests are done by physicians.

Q. Can you tell us anything about gluten intolerance?

A.Gluten intolerance is associated with the disease called gluten-sensitive enteropathy or celiac disease. It is due to an abnormal immune response to gluten, which is a component of wheat and some other grains.

Q. Is it possible that many people who were given the diagnosis of irritable bowel syndrome in the past are turning out to actually have allergies?

A. There is no good evidence that irritable bowel syndrome is due to food allergies in most instances.

Q. This summer I had lunch at a fast food restaurant for the first time and I broke out in hives. The doctor seemed to think maybe it was the sulfites in the food. Now you said there had been regulations for salad bars and sulfites, but in the whole food industry are there regulations for the use of sulfites?

A. Yes, there are industry-wide regulations covering the use of sulfites. Now I do not know anything about the restaurant you ate at, but it is more likely that you ate something else you are allergic to because sulfites rarely cause hives.