The following is a guest post by Kevin Lomangino, one of our story reviewers on HealthNewsReview.org. He is an independent medical journalist and editor who is currently Editor-in-Chief of Clinical Nutrition Insight, a monthly evidence-based newsletter which reviews the scientific literature on nutrition for physicians and dietitians. He tweets as @Klomangino.
Thanks to the recent national debate about the tradeoffs involved with PSA testing and mammograms, we are starting to recognize that cancer screens have the potential to cause more harm than good in some situations. Now I’d like to see this awareness spread to other areas of medicine where tests are widely used without strong supporting evidence.
Why not start with allergy testing?
I was introduced to the problems here when reporting on a recent study about food allergies in children. As a parent of two small children myself, I know that parents often harbor suspicions that their child is allergic to foods like milk, wheat and nuts. But I had no idea the extent to which allergy testing was stoking these fears unnecessarily, leading parents to initiate harmfully restrictive diets.
The study that opened my eyes was conducted at a large academic allergy center whose researchers looked back at the medical records of 125 children. The children had all been avoiding one or more foods because of a suspected food allergy and were referred to the center for evaluation.
Most of the children had previously been given a skin or blood-based allergy test that identified an immune system response to specific foods. These test results were the primary reason that many of the children thought they were allergic to the food.
But as study author David M. Fleischer, MD and his colleagues pointed out, having a reaction to one of these foods on a blood or skin test doesn’t mean you’ll develop allergy symptoms when you actually eat the food. And their study bore this out, showing that in a shocking 93% of cases (103 out of 111), children who were avoiding foods based on an allergy test had no reaction to the food when they ate it during a carefully conducted food challenge.
Most of the children in the study had an allergy-related skin condition called atopic dermatitis, which may have made false-positive test results more likely. However, food allergy tests have also been shown to have poor predictive value in people without this condition, the authors commented. And they warned that a misdiagnosis of food allergy carries significant consequences for developing bodies.
“A growing number of patients referred to our practices are being placed on strict, unproven food elimination diets that have led to poor weight gain and malnutrition,” they wrote.
These false diagnoses can also be very disruptive for families and their surrounding communities. Special diets are a hassle to follow and “non-allergenic” foods often cost more. Children and parents may suffer unnecessary anxiety about accidental ingestion of the wrong food. Even classmates may be affected due to the spread of “nut free zones” that restrict food choices.
So, how did we get into this situation?
Richard Wasserman, MD, PhD, a board certified allergist in Dallas, Texas, told me that allergy test panels are being heavily marketed to doctors as a means to boost practice revenue (a contention supported , indirectly at least, by this recent report in Medical Economics). And despite the fact that these tests have been shown to generate a false-positive result up to 50% of the time when used to detect food allergies, he said that inadequately trained clinicians – mostly primary care physicians but also some allergists – may tell patients to avoid certain foods based solely on a positive allergy test. He added that many patients are probably being tested in situations where a careful clinical history would rule out suspected food allergy.
“Many patients who come to me with suspected food allergies don’t end up getting tested,” he said. “When I take their history, I find out that the patient doesn’t have an adequate knowledge of what a food allergy is. There is no linkage between the history and the problems that they are telling me about, so I don’t test them.”
We should digress here for a brief disclosure: As an allergist, Wasserman acknowledges he may be biased against the growth of allergy testing in primary care, as patients seen at these practices might otherwise come to him for specialist treatment. But his concerns about the overuse of food allergy tests are supported by the authors of recent NIH guidelines on food allergy, who warned that lab tests are frequently (and incorrectly) used as the sole basis for a food allergy diagnosis.
While these new NIH guidelines are definitely a step in the right direction, recent developments suggest that we are still a long way from implementing an evidence-based approach to allergy testing. As reported by Pharmalot.com, the Giant Eagle grocery chain, with support from drugmaker Sanofi (which sells an over-the-counter version of the Allegra allergy medication), is now offering to provide free in-store blood tests that will screen for allergic sensitivity to a variety of food and airborne allergens.
Beyond the dubiousness of a pharmaceutical company offering to tell you whether or not you are candidate for treatment with one of its products, this program generates other concerns about the harms of indiscriminate allergy screening. Given the high false-positive rate for food allergy tests, this program seems very likely to result in people wrongly avoiding foods that they would have no trouble eating. And while tests for airborne allergens are more accurate, they are still likely to result in some people receiving unnecessary treatment as well as other problems that could be avoided with a more careful evaluation.
Illustrating such an example, Wasserman discussed a hypothetical Giant Eagle customer with nasal symptoms who received a false-positive test for allergy to ragweed. That person might start taking Allegra in the mistaken belief that it will reduce their symptoms. But an expert clinical evaluation might have turned up a more serious ailment whose discovery was delayed because of the false test result.
“A positive test does not equal a diagnosis, which is the premise of the testing programs,” Wasserman said. “These tests are fundamentally useless without a formal evaluation of the patient.”
(Giant Eagle does say that a letter sent with the test results will encourage customers to “share their results with their healthcare provider,” but how many will do so?)
Of course, none of this is meant to discount the
importance of detecting and treating food and other allergies, which do seem to be on the rise and which can cause serious and even fatal reactions. My point is that indiscriminate testing for allergies may be even worse that not enough testing.
Like prostate cancer and breast cancer, allergies are a public health problem that we simply can’t test our way out of.