Specialists who treat people with life-threatening food allergies are advocating wider use of an available blood test to reduce the need for a potentially dangerous and terrifying procedure called an oral challenge.
"When you tell a person they have a food allergy, it is a lifestyle altering diagnosis," said Dr. Kathleen Sheerin, an allergist in Atlanta. "So you want to make sure that you confirm that diagnosis."
Oral challenge involves giving food to a patient that could cause violently illness or even death. The test procedure bedevils doctors as well as patients, said Dr. Hugh Sampson, professor of pediatrics at the Mount Sinai School of Medicine in New York City.
"When I get a person who comes in with a suspected food allergy, I will do a skin test first to see if they have antibodies to a food," Sampson told United Press International during the annual meeting of the American Academy of Allergy, Asthma and Immunology.
If there is a reaction, Sampson said he will take a blood sample from the patient and perform what is known as an Immuno-CAP blood allergy test for certain food allergies. The commercially available product gives doctors a measurement of antibodies being produced in the body that are 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. If they are above a certain point I can tell the patient they will react," Sampson said, "without having to go through an oral challenge." He estimated the accurate blood test could eliminate the need to do about half the oral challenges.
"The CAP test is accurate enough now to give us reliable results for patients with egg, peanut, fish and milk allergies," he said. "I think the blood test has the potential to make our diagnoses much more accurate."
Often, however, even with skin tests, oral challenges are required because even though skin tests might show a reaction, there is a large discrepancy between appearance of a "wheal" on the skin of a patient suspected of having a food allergy and patients who really have food allergies.
That is because skin tests for food allergies are subject to many variables. For example, "the results can be different if done on the right arm or the left arm and even in different places on the back," said Dr. John Oppenheimer, clinical associate professor of internal medicine at the University of Medicine and Dentistry of New Jersey in Newark.
"None of the reagents we use for skin testing is standardized," said Sampson. "The ... test is different from individual to individual."
In addition, Oppenheimer said results can vary depending upon how a 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.
Reactions from oral challenges can be sudden and dramatic. "I've had patients who would be given some food and the next thing they are vomiting on the nurses," said Sheerin, vice chairwoman of AAAAI's public education committee.
"I've done over 4,000 oral challenges," said Sampson, "and I'm prepared to use epinephrine to stop the reaction as soon as it starts. So far, I'm glad to say that none of my patients have died from the oral challenge. However, 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 Sampson and Sheerin and other doctors welcome the Immuno-CAP blood test. "If a CAP is positive for a certain food above a certain level," said Dr. William Dolen, professor of medicine at the Medical College of Georgia, Augusta, "the near certainty that is clinically relevant keeps you from having to do a food challenge. But if it is below that level then you really do need a food challenge to be sure."
Sampson said although the blood test is particularly helpful in making diagnoses without putting patients at risk -- and costs only about $25 -- even the blood test needs work. He said continued research is needed to expand use of the blood test for other food allergens.
Sheerin noted the blood test requires that blood be drawn from the vein, a procedure than can be a problem if the patient is a squirming 2-year-old with small veins and a fear of needles.
Sampson also suggested the blood test might be able to be used to perform serial tests on patients to see if they have "outgrown" their allergies. Although few people outgrow peanut allergies, he added, patients often will no longer be sensitive to egg and milk allergies as they mature.
Labeling someone with a food allergy diagnosis -- especially a peanut allergy -- can be devastating, said Dr. Robert Zeiger, clinical professor of pediatrics at the University of California, San Diego.
Reactions to peanuts can be fatal and about 125 people die each year from such reactions, Sampson said. But peanut and peanut residues that are enough to cause substantial anaphylactic, or allergic, shock can hide in common foods such as peanut oil used in cooking movie theater popcorn.
Some people diagnosed with peanut allergies are so fearful of suffering reactions to the food they will not eat outside their own homes -- avoiding parties at their friends' homes, restaurants, even candy bars from machines -- or spend hours scrutinizing ingredient labels, even though some labels are misleading about peanut products used in food manufacturing.
"There are people who are skin testers and people who are blood testers. I don't really care. I just want as good an answer as I can get," Sampson said.
