Jewish World Review April 25, 2003 / 23 Nisan, 5763

For food allergies, researchers recommend more accurate blood test over common skin test

By Ed Susman | "You're allergic to peanuts.'' When a doctors makes that announcement, he doesn't just mean you'll have to stop eating peanut-butter-and-jelly sandwiches. He means you're going to have to make a lifestyle change. Peanuts, peanut oils and other peanut products are everywhere in today's world, and you're going to have to quiz waiters and chefs about ingredients. You'll have to avoid the neighbor's freshly baked cookies. You'll probably have to carry a syringe and medical kit in the event of a surprise allergy attack.

In fact, a hundred or more people die each year from allergic reactions to foods, and mostly to peanuts. So a diagnosis must be accurate. For this reason, many researchers believe that physicians should be using a diagnostic blood test more frequently -- rather than relying on the skin-prick test that has been used for decades and which is notorious for errors -- to determine a person's allergic response.

"When you tell a person he have a food allergy, it's a lifestyle-altering diagnosis,'' said Kathleen Sheerin, M.D., an allergist in Atlanta, Ga. "So you want to make sure that diagnosis is correct.''

Skin tests for food allergies have been used for decades, and many allergists still rely on them exclusively, Sheerin said. In general, if a patient has a positive skin test, the physician confirms the allergy by administering the suspected food in his or her office -- with emergency medication handy, in case the skin test is correct.

Hugh Sampson, M.D., a professor of pediatrics at Mount Sinai School of Medicine in New York City, said that when a patient comes in with a suspected food allergy, he'll first administer a skin test to check for antibodies to food. Speaking before the recent annual meeting of the American Academy of Allergy, Asthma and Immunology in Denver, Colo., Sampson explained that he then takes a blood sample to perform a blood test -- known as an Immuno-CAP blood allergy test -- to measure the antibodies being produced in the body caused by specific allergens.

"With certain food allergies, the Immuno-CAP test gives us enough information to be able to tell patient if he or she has a food allergy,'' he said. "If the measurements are above a certain point, I can tell the patient that he will react. ''

"That's because skin tests for food allergies are subject to a number of variables that can influence the appearance of wheals,'' said Dr. John Oppenheimer, a clinical associate professor of internal medicine at the University of Medicine and Dentistry of New Jersey in Newark.

The results can differ, for example, if they're done on the right arm or the left arm, and even in different places on the back, he said. In addition, results may depend on how hard the nurse or doctor punctures the skin, the type of device used to puncture the skin, the angle at which the device enters the skin and how the tests are scored and described.

And Sampson added that none of the "re-agents'' -- the food extracts used in skin testing -- are standardized. Techniques differ, he said. For example, if a doctor suspects that a person is susceptible to egg-based allergens, he could use a commercial egg allergen re-agent, or he could make his own re-agent by mashing up eggs in his office.

But most important, when oral challenges are required, the reaction can be sudden and dramatic. "I've had patients who would be given a food,'' said Sheerin, "and the next moment, they are vomiting on the nurses.''

Sampson said he's done more than 4,000 oral challenges in his office, and that he's had no patient deaths. "However,'' he explained, "when we tell patients and their parents the possible outcomes of an oral challenge, one of the possibilities on that consent form is death.''

That's why he welcomes increased use of the Immuno-CAP blood test.

"If a CAP is positive for a certain food above a certain level,'' said Dr. William Dolen, a professor of medicine at the Medical College of Georgia in Augusta, "the near certainty ... keeps you from having to do a food challenge.''

Sheerin suggested that use of the blood test would probably eliminate 50 percent of the oral food challenges. The blood test has the added advantage of being standardized, she said.

It was noted that while the blood test is especially helpful in making a diagnoses without putting patients at risk -- and can do so relatively inexpensively because the test costs about $25 -- even that method of diagnosis has some problems.

Continued testing is needed to expand the uses of the test for more food allergens, said Sampson. And the blood test requires that blood be drawn from a vein, a procedure than can be a problem if the patient is a squirming 2-year-old with an understandable fear of needles.

Sampson suggested that the blood test might also be used to perform serial tests on patients to see if they have "outgrown'' their allergies. While few people outgrow peanut allergies, he said, children will often grow less sensitive to egg and milk as they mature.

A food allergy diagnosis -- especially a peanut allergy -- can be devastating to the patient, said Dr. Robert Zeiger, a clinical professor of pediatrics at the University of California at San Diego. Peanut and peanut residues that are enough to cause substantial anaphylactic shock -- difficulty breathing or swallowing, and a sudden drop in blood pressure that may occur within seconds -- can hide in the most common foods, such as peanut oil used in cooking movie theater popcorn.

Some people diagnosed with peanut allergies are so fearful of suffering allergic reactions that they will not eat food outside their own homes -- avoiding parties, restaurants, even candy from vending machines. In some cases, peanut residue on a table or plate can cause a severe reaction; the fumes from cooking or from someone nearby eating the suspected food may serve as triggers. Patients may spend hours scrutinizing ingredient labels, even though some labels are vague or misleading about whether peanuts are used in manufacture of the product.

"There are people who are skin testers and people who are blood testers,'' Sampson said of the controversy between the two testing procedures. "I don't really care. I just want as good an answer as I can get.''

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