Blood test results can vary widely - allergy diagnosis - Brief Article - Evaluation

The results of most commonly used blood tests for allergies can vary widely, depending on which laboratory does the actual testing and what procedure is used. This means that many people who are tested for allergies using these procedures may be misdiagnosed, argues Sheryl Szeinbach, professor of pharmacy, Ohio State University, Columbus.

In a study, researchers obtained blood from 26 people with known allergies and then sent samples from each individual to six commercial laboratories. Each of the laboratories used one of three common blood tests--the RAST, AlaSTAT, and 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.

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

Szeinbach emphasizes that "Results from separate labs should be accurate and interchangeable, regardless of the procedure used. 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 cautions. For example, false positive results could lead doctors to treat patients for a specific allergy when the symptoms really have been caused by something else. "Misdiagnosing patients can result in unnecessary treatments or the omission of effective interventions....

"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. It also reinforces the idea that there needs to be a standard method for detecting allergies."

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