[In the upcoming series of posts, I will discuss each of the 5 “Choosing Wisely” talking points.  These were established by the American Board of Internal Medicine in conjunction with nine subspecialty boards as well as Consumer Reports to educate patients regarding the appropriate use of diagnostic tests and procedures.  Each specialty was asked to discuss 5 commonly used tests or procedures in their respective field whose use should be questioned or at least evaluated critically.  Here is a link to the Allergy/Immunology talking points: http://choosingwisely.org/wp-content/uploads/2012/04/5things_12_factsheet_AAAAI.pdf]

Don’t perform unproven diagnostic tests, such as immunoglobulin G (IgG) testing or an indiscriminate battery of immunoglobulin E (IgE) tests, in the evaluation of allergy.

Often, in the quest for answers, both patients and physicians alike place an enormous amount of stock in laboratory testing.  While very helpful diagnostically when used rationally, there are numerous scenarios where inappropriate use of diagnostic testing can lead to confusing results or worse yet, unnecessary or even potentially harmful interventions.  That’s why it is critical for any laboratory testing to be coupled with a thorough patient history to answer a clinically relevant question.  For any lab test, in order for it to have much utility, I would argue at least two conditions should be met: a) it should be a good test to detect what you are looking for and not show positive for irrelevant conditions (both sensitive and specific) and b) it should provide actionable data.  By “actionable”, I mean that you should do something based on the result, whether this is prescribe a medicine, recommend a treatment, etc.  There is zero point in arbitrary testing if the clinician does not change the course of action based on the testing.

An excellent example of such inappropriate testing can be seen in the realm of food allergy testing.  It is not uncommon for an allergist to receive a referral to evaluate a child for food allergy after a large panel of IgE-specific food allergy testing was performed.  While IgE-specific food allergy tests can be useful, I would add several caveats:

• For only a few commonly allergenic foods (milk, soy, wheat, fish, peanuts, tree nuts) is there reliable data available to know how to interpret a specific value from the test, i.e., for peanut, a value of > 14 kUA/L is highly predictive of a likely reaction to peanut
  

• IgE-based testing is available for many, many foods and other substances, but all I could reasonably say about about a positive value for something like eggplant, for instance, is that you have IgE antibodies against eggplant in your system.  This does not mean you will have a reaction to eggplant, nor should you necessarily restrict eggplant from your diet.
  

• A positive allergy test to food does not mean that the patient has a food allergy.  A food allergy is established when there is a clear clinical history of an immediate reaction (usually respiratory, GI, or skin symptoms) after ingestion of a specific food which is then confirmed with a positive test to that food.  For the classic food allergy, this would almost always happen within minutes to at most half an hour of eating the food.  There are rare examples of delayed reactions to certain foods, but these are uncommon.
  

• Dietary restriction of certain foods based on IgE testing alone without any clinical history of a food reaction is at best unnecessary, and at worst, potentially harmful if nutritious foods are being excluded from the diet.
  

• ​The gold standard to prove a food allergy is an oral food challenge, where the suspected food is given in a controlled medical setting.  This is often not necessary if the diagnosis is clear from the clinical history coupled with intelligent confirmatory testing, but can be used in circumstances where the history is more nebulous and the clinician would like to rule out a certain food from having a role.  It might also be pursued if a child is suspected of having lost a sensitivity to a food (which occurs over time for most food allergens, in fact, with the notable exception of peanut) and the parents would like to establish that the child can eat that food safely.  If a patient has a very clear-cut and serious reaction to a certain food, a food challenge is unnecessary and in fact potentially dangerous.
  

It is important to distinguish IgE-based testing from IgG-based testing.  IgE is the antibody that provokes immediate-type reactions, and is relevant for food allergy testing.  IgG tests for many foods are available commercially, and while many people will have detectable IgG antibodies to any number of foods, there is no relevance of IgG to foods in food allergy.  Despite that, these tests are readily available and are ordered routinely in non-expert assessment of “food allergy”.  IgG-based food allergy testing is just one of a very large spectrum of unproven diagnostic tests that are available, but unhelpful.

As you can see, diagnosing food allergy is much more complex than one might imagine.  It is certainly not just a matter of “ordering the test”.  Choosing wisely implies ordering a scientifically validated test that works to confirm clinical suspicion based on a thorough history and importantly, understanding how to interpret that test based upon knowledge of the efficacy and limitations of that test.

I, like all the physicians at Allergy Partners, strive to practice the highest quality, evidence-based, and cost-effective medicine by utilizing effective and intelligent testing.  You can rest assured that we will never use unproven tests, and that we adhere to rigorous standards when choosing what tests to order and how to interpret these tests.  This is the only way we can ensure that we continue to deliver consistent, scientifically driven care when there are so many poorly validated and frankly worthless tests available.

Thanks and I hope this was informative!  I will continue to discuss the other points in the “Choosing Wisely” document in future posts.

Cheers,

Dave Fitzhugh, MD