Not All Allergy Tests Are Created Equal

Contact: Sheryl Szeinbach, 614-688-4249

Written by Holly Wagner, 614-292-8310[email protected]

NOT ALL ALLERGY TESTS ARE CREATED EQUAL, STUDY SUGGESTS

COLUMBUS, Ohio - The results of most commonly used blood tests for allergies can vary widely depending on which laboratory does the actual testing - and which laboratory procedure is used, a new study suggests.

This means that many people who are tested for allergies using these tests may be misdiagnosed, said Sheryl Szeinbach, a study co-author and a professor of pharmacy at Ohio State University.

Researchers obtained blood samples from 26 people with known allergies and then sent samples from each individual to six commercial laboratories. Each of the six laboratories used one of three common blood tests -- the RAST, AlaSTAT and the ImmunoCap - to test for allergies. The researchers compared the results of each test and found that only the labs using the Pharmacia ImmunoCap test had produced similar results, Szeinbach said.

Results from the two labs that used the ImmunoCap test agreed 98 percent of the time. However, results from the other two tests varied in agreement by as much as 50 percent, depending on the testing lab.

"The practical value of any lab test rests in its ability to give accurate, consistent and therefore reliable results," Szeinbach said. "With the exception of one test, we found that different labs gave significantly different results even when they used the same test format.

"The ImmunoCap blood test proved to be highly accurate and reliable when used to measure IgE in patients with allergies or allergy-like symptoms."

The point of the study was to judge how the results of these different tests compare with one another in everyday use, she said.

The research appears in the April issue of the journal Annals of Allergy, Asthma, & Immunology.

In this study, the researchers sent serum samples from 26 patients to six labs for testing. Serum is the fluid portion of the blood that contains antibodies - an immune compound that fights invaders. Each testing method detected the presence of immunoglobulin E (IgE) for different allergens. IgE is an antibody that causes allergic symptoms.

Each lab used their usual procedures to test the serum samples for IgE antibodies to 17 common allergens, including cat and dog dander; Bermuda and timothy grasses; ragweed; and mold such as penicillin and C. albicans, the cause of yeast infections.

The researchers sent three sets of each serum sample to each lab. Three labs used a modified RAST format method, two used the ImmunoCap method, and one used the AlaSTAT method.

"Results from separate labs should be accurate and interchangeable, regardless of the procedure used," Szeinbach said. "But this study showed that uniformity doesn't exist for some of the currently available commercial allergy tests."

Inaccurate tests can have real costs to patients, she said. For example, false positive results could lead doctors to treat patients for a specific allergy when the symptoms are really caused by something else. "Misdiagnosing patients can result in unnecessary treatments or the omission of effective interventions," she said.

"Overall, none of the IgE tests we evaluated were terrible," she said. "Some simply performed better than others. We want to reduce the uncertainty in allergy diagnoses.

"And although we can't monitor the lab work directly, we can only infer that the problems we found in this study might be attributed to some laboratories using poor testing procedures and inadequate tests," she said. "It also reinforces the idea that there needs to be a standard method for detecting allergies."

This research was supported by a grant from Pharmacia - the maker of the ImmunoCap test -- and Upjohn Diagnostics Division based in Kalamazoo, Mich.

Szeinbach co-authored the study with James Barnes, of the University of Mississippi; Timothy Sullivan, of Emory University School of Medicine; and P. Brock Williams, of the University of Missouri Medical School.

###