A skeptical take on allergy testing

RUN FOR YOUR LIVES!!! (photo by H. Zell)

This is the second of three segments that I presented on The Reality Check, Canada’s weekly skeptical podcast.  On episode #205, I talked about allergy testing.  Advances in medicine have completely eradicated diseases such as smallpox, and we are well on our way to doing the same for polio.  Yet more diseases are firmly under control through most of the developed world through the use of vaccines.  However, as we remove some causes of ill health, we notice that others have grown in prominence over the past few decades.  Allergies are a good example of one of these increasingly diagnosed conditions, but the general public tends to have a fairly poor understanding of what allergies are, how they come about and how they can be diagnosed.

What are “allergies”?

First, we need to define what we mean by “allergy”, because people are often confused by the difference between “allergy”, “intolerance”, and “sensitivity”.

  • Food allergy is an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food. The main sources of food allergy (which account for around 90% of food allergies) are called the “big eight”: milk, eggs, soy and wheat (which usually resolve), and peanuts, tree nuts, seafood, shellfish (which usually persist).  Other common allergens are dust mites, pollen, animal fur and bee/wasp stings.  In a food allergy, the body’s immune system responds to harmless molecules like those I just mentioned by producing antibodies (called immunoglobulin E, or “IgE”).  The next time that the body encounters that allergen, those antibodies trigger a completely unnecessary and very rapid immune response which can range from irritating (think hayfever) to potentially dangerous (think constriction of the airways).  Other allergies are not mediated by IgE, including celiac disease.  In celiac disease, a protein found in wheat and some other plants causes a reaction in the gut that results in the immune system attacking the gut wall.  This leads to inflammation and problems absorbing nutrients.
  • Non-immunologic adverse reactions to food are termed food intolerance and include conditions such as lactase deficiency.  Lactose is a sugar molecule made up of two different molecules bonded together and needs to be broken apart to be absorbed across the wall of the intestine.  When lactase, the enzyme that breaks down lactose is absent, the lactose stays in the gut and is used as a food source by bacteria there.  The metabolism of those bacteria produces large amounts of gas as a by product and it is that gas that causes the unpleasant symptoms of lactose intolerance.
  • Food sensitivity is a nonspecific term that can include any symptom perceived to be related to food and thus may be subject to a wide range of usage and interpretation.

What is the best way to diagnose allergies?

It seems that there is an increase in the prevalence of allergies, but much of this evidence is based on self-reporting which is notoriously inaccurate.  Studies have shown that only about 1 in 10 adults who think they have an allergy actually show symptoms, and only 1 in 5 children whose parents think they have an allergy show symptoms under clinical testing.  Also, the number of people suffering from allergies is very small, which means that a seemingly large increase in relative risk actually means a very small change in absolute risk (think of a doubling in risk between 1 case per 100 people and 2 cases per 100 people).  There is no way to predict who is going to suffer from allergies or how severe the allergic reactions will be without good diagnosis.  Even then, the severity of the reaction can vary and allergies can resolve in relatively short periods of time.  A range of unproven allergy tests are available and these vary widely in how useful they actually are.  These tests can be grouped into three categories:

  • Tests which are invalid for any purpose, and not based on scientific fact (there are more in the links in the show notes, but I’ll cover a few of my favourites here)
    • Cytotoxic Testing – popular in the 1980s, this simply involves taking a drop of blood and adding an allergen then watching under a microscope for a reaction.  It is utter bullshit.
    • Provocation-Neutralization – this involves eating or injecting allergens in a higher dose (called the “provocation”) and then a lower dose (called the “neutralisation”).  It is claimed that this cures allergies.  It is utter flimflam.
    • Electrodermal Diagnosis – uses the galvanic skin response (changes in skin conductivity) with and without the allergen.  It is utter balderdash.
    • Applied Kinesiology – the same pseudoscientific test used to demonstrate the effectiveness of power balance bands (those 10cent rubber bands that people pay $60 for).  It is utter claptrap.  For those of you interested in applied kinesiology, here is Richard Saunders’ explanation of how it works:
    • Reaginic Pulse – this test involves monitoring a patient’s pulse before and after the administration of an allergen.  If there is a change you are allergic!  It is utter hogwash.
    • Body Chemical Analysis – this sounds more scientific and uses expensive and technologically advanced medical instruments to detect small changes in certain chemicals in the body.  Unfortunately, there is not evidence that any of these chemicals influence allergies, so it is utter rubbish.
  • Tests which are valid for other medical conditions, but not for the evaluation of allergies
    • Measurement of IgG Antibodies – What would you think if I offered you an allergy test involving an “immunoglobulin G enzyme-linked immunosorbent assay”.  Scott Gavura at Science Based Medicine has a very detailed take-down of this particular test [1].  This kind of test has been offered by private companies through pharmacies in a number of different countries, and costs range from $150-$450.  The tests, including brands such as “HEMOCODE”, or “YORKTEST’s FoodSCAN”, purport to evaluate around 250 foods based on a small blood sample, and to provide a detailed and individualised diet modification plan to help you avoid them.  Briefly, IgG detects and protects against invading pathogens as well as passing across the placenta to give passive immunity to the foetus.  However, IgG is produced in response to consuming foods, not in response to allergies to them, and elevated IgG levels have been shown to be a marker of food tolerance, not intolerance!  IgG is not a reliable indicator of allergies.  Furthermore, these tests are often aimed at identifying food intolerance, which does not even involve the immune system (such as IgG, remember back to lactose intolerance).  How are they to know they are being scammed…?
  • Tests which do actually work
      • Skin prick test – the skin is pricked in a number of locations and either saline solution or the allergen is applied.  If the resulting reaction to the allergen is greater than the reaction to the saline solution by a certain amount then the test is considered to be “positive”.  The test is looking for the IgE antibodies that are characteristic of an allergy.  The problem with this test (and the associated blood test, which accomplishes much the same thing) is that there is very high false positive rate of around 50%.  In other words, if the test says that you have an allergy, there is only a 50% chance that you actually do have an allergy.  Furthermore, even patients with true positives might not notice, or might tolerate their allergy – so the detected allergy might not be clinically significant.  However, the SPT is useful in that it has only a 5% false negative rate, so if the test says that you don’t have an allergy you can be pretty sure it is correct [2].
    The “skin prick test” for allergies
    • Double blind, placebo controlled oral challenges – these have been described as the “gold standard” of allergy testing.  The false positive rate is somewhere between 0.7% and 12.9% (with the higher figure likely due to the nocebo effect).  Meanwhile the false negative rate is around 3%.  In other words, the test accurately distinguishes between patients who have and do not have allergies.  Following a negative test, the patient is often presented with the proposed allergen in a normal meal-sized portion to verify the result.

What can we do to help prevent allergies in the first place?

EpiPens – sometimes life-saving, but do they contribute to fear and anxiety?

Currently, the American Academy of Pediatrics recommends that high-risk infants be exclusively breast-fed, that lactating mothers avoid peanuts and nuts to avoid sensitization through breast milk, that the introduction of solids be delayed until 6 months of age, and that major allergens, such as peanuts, nuts, and seafood, be introduced after 3 years of age [3].  Others have suggested that this avoidance in early life actually heightens allergic reactions later in life[4].  It has been estimated that giving an EpiPen to every UK school child with an allergy would cost $37m per life saved [5], and the over-prescription of these instruments increases tension and stress among parents and children, although this argument has been disputed.  Some have argued that the increased perception of allergies and perhaps even some allergic reactions themselves are due to a form of mass hysteria brought on by the very very few high profile cases of death from allergic reactions and the extreme measures taken to limit children’s exposure (such as the evacuation of school buses because a single peanut was found on the floor) [6].  There may be “allergen vaccines” on the market at some point, but drastic steps like infecting yourself with tropical diseases in order to “train your immune system” are probably unwise except for under clinical conditions.

Conclusions

  • Allergies are a widespread problem, but very rarely fatal.
  • The psychological and social implications of current fears about allergies may be contributing to a reduction in health and well-being, even in healthy people, and are almost certainly increasing rates of self-reported allergies.
  • There needs to be a strong evidence base to provide accurate diagnosis of allergies.  Right now, there are very few accurate diagnostic tools, and many that are currently used only serve to increase patient anxiety by providing either false positives or by diagnosing clinically-insignificant levels of allergy.
  • The public need to be educated about allergies in such a way as to empower them to act in the case of an allergy without causing undue stress and anxiety.
  • Most importantly, if you are concerned about allergies, consult your doctor – preferably a real doctor, rather than a homeopath, naturopath or chiropractor.

Further reading

http://pollen.utulsa.edu/Practice%20Parameters.pdf – Allergy Diagnostic Testing: An Updated Practice Parameter

http://www.cmaj.ca/content/early/2012/03/19/cmaj.110026.citation – review of allergy testing

http://www.companiesandmarkets.com/Market/Healthcare-and-Medical/Market-Research/Food-Allergy-and-Intolerance-Products-A-Global-Strategic-Business-Report/RPT936493 – projection of increase in allergies and intolerance products  value to $26 billion.

http://ehp03.niehs.nih.gov/article/info:doi/10.1289/ehp.5702 – overview of allergies.

http://www.jacionline.org/article/PIIS0091674904011455/fulltext – technical but comprehensive overview of the range of types of allergies

http://allergies.about.com/od/controversialtherapies/a/unprovendx.htm – interesting list of tests that don’t work for allergies.

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