I spend a lot of time as a pharmacist discussing side effects and allergies to drugs. For your own safety, I won’t recommend or dispense a drug until I know your allergy status. I don’t limit the history to drugs—I want to know anything you’re allergic to, be it environmental, food, insects, or anything else. Allergies can create true therapeutic challenges: We can’t dismiss any allergy claim, but as I’ve blogged before, there’s a big gap between what many perceive as an allergy and what is clinically considered a true allergy. My concern is not only avoiding the harm of an allergic reaction, but also avoiding the potential consequences from selecting a suboptimal therapy that may in fact be appropriate. You may need a specific drug someday, so  I encourage patients to discuss vague drug allergies with their physician, and request allergist testing as required.

Food allergies can be as real as drug allergies, and are arguably much harder to prevent. We can usually control when we get penicillin. But what about peanuts, eggs, or milk, all of which can also cause life-threatening anaphylaxis?  Food allergies seems to be growing: not only anaphylaxis, but more people believe they have some sort of allergy to food.  Allergy is sometimes confused with the term “intolerance”, which seems more common, possibly as the availability of “food intolerance testing” grows. Food intolerance testing and screening is particularly popular among alternative practitioners. Testing can take different forms, but generally the consumer is screened against hundreds of food products and food additives. They are then provided with a list of foods they are “intolerant” to. I’ve spoken with consumers who are struggling to overhaul their diet, having been advised that they are actually intolerant to many of their favourite foods. These reports are taken seriously by patients who believe that they’ll feel better if they eliminate these products. In the pharmacy, I’ve been asked to verify the absence of trace amounts of different fillers in medications because of a perceived intolerance.  Children may be tested, too, and parents may be given a long list of foods they are told their child is intolerant of. I’ve seen the effects in the community, too. Think going “peanut free” is tough? A public school in my area sent home a list of forbidden food products: dairy, eggs, bananas, tree nuts, peanuts, soy, sesame, flax seed, kiwi, chicken, and bacon. Were these all true allergies? It’s not disclosed. Anaphylactic or not, the parents had informed the school, and the school had banned the food product.

But can a simple blood test actually identify and eliminate food intolerance? That’s the question I wanted to answer.

When it comes to food intolerance testing, blood tests are just the start. Other methods used include vega testing, the K-Test, hair testing,and  applied kinesiology. But the blood tests are enjoying new popularity—and even pharmacies are now actively promoting these tests:

You might love food, but some food might not love you

The HEMOCODE Food Intolerance System can unlock your hidden food sensitivities

Speak with your Rexall Pharmacist today to learn about a painless blood test that can identify over 250 common foods that may be causing you unpleasant symptoms such as chronic fatigue, migraines, back pain, fibromyalgia, psoriasis, acne, diarrhea and constipation.

There’s a short video (above) that is very illustrative. Narrated by a pharmacist, it describes that a simple fingertip blood test is used to screen blood against 250 items. Test results are then reviewed by “naturopathic medical professionals” who will describe the foods and other products that you are intolerant to, and your degree of intolerance. You’re also advised:

Your personalized results also include recommended vitamins and supplements that are uniquely suited to the customer, based on the foods that are suggested to be eliminated from your diet, which are themselves, uniquely personal.

So the $450 blood test, includes dietary change recommendations as well as vitamin and supplement recommendation. The vendor explains it as follows:

By adding personalized vitamin and supplement recommendations, the Hemocode System will help consumers move towards optimal nutrition as they work to eliminate offending foods from their diets. No other food intolerance program offers this type of seamlessly delivered, highly customized solution. In addition to delivering a meaningful wellness benefit to their customers, the inclusion of dietary supplement recommendations as part of Hemocode creates an opportunity for retailers to recognize: accretive revenue from Hemocode System sales; incremental growth in their core vitamin program and an enhancement of their market differentiation.

This testing is also positioned as a weight loss plan:

Would I be able to lose weight with HEMOCODE?
Your chances of permanent success are excellent: HEMOCODE(TM) works differently than other conventional diets and rules out the yoyo-effect.

Is HEMOCODE a miracle diet?
It is not a miracle diet, but a scientifically based diet modification. Unlocking your HEMOCODE(TM) gets to the root of your problem. Food intolerances can be the cause of a weight problem and inhibit the success of losing weight with conventional diets. The HEMOCODE(TM) test looks at foods on a one-by-one basis for individual intolerances.

Hemocode is just one of several blood tests that’s marketed. There’s also the YorkTest in the United Kingdom and also Canada:

Food intolerance is all about how your bodys immune system the bodys natural defence against foreign substances, such as poisons and harmful bacteria reacts to specific foods. [sic]

Food intolerances are believed to arise when certain, incompletely digested food particles enter your bloodstream and are treated as foreign substances. This results in your immune system producing tailor-made antibodies (IgG), which attack the food in question. Some researchers believe this inflammatory response in the body can increase certain symptoms. Food intolerance has been associated with Irritable Bowel Syndrome (IBS), bloating, tiredness, constipation, diarrhea, cramping, eczema, headaches and migraines.

So just what is the evidence supporting the use of food intolerance tests?

Testing Principles

Diagnostic tests can be as pseudoscientific as treatments. To evaluate, we ask the following:

  • Analytic validity: How reliable is the testing? This includes within-laboratory and between-laboratory precision.
  • Clinical validity: How consistently and accurately does the test detect an objectively-measured clinical status? The test should be both sensitive (few  false negatives) and specific (few false positives). Patients in the same circumstances should consistently have the same test results.
  • Clinical utility: What is the natural history of the disorder? Will the use of the test make any difference in the outcome? Interventions taken should be evaluated and compared against no testing.
  • Ethical, legal, or social implications : What are the potential patient consequences of the use of the test, and its results? What if the results are erroneous?

It all boils down to a single question that must be satisfactorily answered before we proceed with testing: How has this test been validated?

What’s a Food Intolerance Blood Test Actually Testing?

Hemocode is an IgG blood test, according to the manufacturer (text now removed; cached version here):

The Hemocode System is a finger prick test that identifies specific immune system-based food intolerances.

Everything we eat can elicit a positive or negative reaction in the body. If you are intolerant to a certain food and you continue to eat it, your body will mount an inflammatory reaction which may manifest in a variety of lifestyle-affecting conditions such as headaches, chronic pain, digestive disorders and many other issues

The Hemocode food intolerance test is a statistically proven, doctor and pharmacist recommended IgG-related test that determines which foods are causing negative reactions.

The YorkTest is also an IgG test. There is no published information in the literature that describes either the Hemocode or the Yorktest, or their analytic validity for any of the products tested for.

Understanding IgE, allergies, and what IgG means

Food allergies are reaction to food proteins. They may be categorized as immunoglobulin E (IgE)–mediated (immediate) reactions, non–IgE-mediated (delayed) hypersensitivity reactions, and mixed reactions. IgE-mediated reactions are the ones we worry about when we hear about a “food allergy”: flushing, itchy skin, wheezing, vomiting, throat swelling, and even anaphylaxis. These reactions can occur immediately following exposure, and are the consequence of the interaction of allergens with IgE located on mast cells. The interaction causes the release of inflammatory chemicals like histamine and leucotriene, triggering the the allergic response which is typically skin related (itchiness, swelling and rash)  but may be anaphylactic as well.

Not all reactions follow this cascade. Non-IgE-mediated allergic reactions can cause localized (e.g., contact dermatitis) or generalized reactions, which are usually gastrointestinal or dermatological in nature. Celiac disease is a non-IgE related allergic reaction. Finally, some allergic disorders are both IgE and non-IgE mediated, such as atopic dermatitis (eczema).

Beyond the IgE mediated reactions, there are a number of possible reactions to food, which may be termed “food intolerances”. Not immune-system based, they’re more common than allergies. They include conditions like lactose intolerance, gastroesophageal reflux (GERD), enzyme deficiencies, metabolic conditions, infections and other processes. It’s a catch-all term by definition.

So where does immunoglobulin G (IgG) come in? IgG molecules mediate interactions of cells with different cellular and humoral mechanisms. IgG antibodies signify exposure to products—not allergy. IgG may actually be a marker for food tolerance, not intolerance, some research suggests:

That research is continuing. But given the lack of correlation between the presence of IgG and physical manifestations of illness, IgG testing is considered unproven as a diagnostic agent as the results lack clinical utility as a tool for dietary modification or food elimination.

The Evidence Check

I sought to understand the literature supporting IgG blood tests. There are no citations on the Hemocode website, and the term Hemocode does not appear in Pubmed. The Yorktest website cites a placebo-controlled study which it claims demonstrates its IgG test reduced symptoms in patients already diagnosed with irritable bowel syndrome (IBS). This finding has been criticized for multiple shortcomings, suggesting the effectiveness of the test in this population remains to be established.

In light of the lack of published clinical trials that validate Hemocode or Yorktest, I looked for consensus opinions and statements on IgG testing from allergy and immunology experts. Here’s what I found, emphasis added:

From the American Academy of Allergy, Asthma and Immunology & American College of Allergy, Asthma and Immunology: Allergy diagnostic testing: an updated practice parameter:

IgG and IgG subclass antibody tests for food allergy do not have clinical relevance, are not validated, lack sufficient quality control, and should not be performed.

And from the the American Academy of Allergy, Asthma and Immunology (AAAAI) Practice Paper, Current approach to the diagnosis and management of adverse reactions to foods [PDF]:

Some tests are considered unproven in regard to the diagnosis of specific food allergies. Those for which there is no evidence of validity include provocation-neutralization, cytotoxic tests, muscle response testing (applied kinesiology), electrodermal testing, the “reaginic” pulse test, and chemical analysis of body tissues. Measurement of specific IgG antibodies to foods is also unproven as a diagnostic tool.

From the European Academy of Allergy and Clinical Immunology [PDF]:

Testing for blood IgG4 against different foods is performed with large-scale screening for hundreds of food items by enzyme—linked immunosorbent assay-type and radioallergosorbent-type assays in young children, adolescents and adults. However, many serum samples show positive IgG4 results without corresponding clinical symptoms. These findings, combined with the lack of convincing evidence for histamine-releasing properties of IgG4 in humans, and lack of any controlled studies on the diagnostic value of IgG4 testing in food allergy, do not provide any basis for the hypothesis that food-specific IgG4 should be attributed with an effector role in food hypersensitivity.

In contrast to the disputed beliefs, IgG4 against foods indicates that the organism has been repeatedly exposed to food components, recognized as foreign proteins by the immune system. Its presence should not be considered as a factor which induces hypersensitivity, but rather as an indicator for immunological tolerance, linked to the activity of regulatory T cells. In conclusion, food-specific IgG4 does not indicate (imminent) food allergy or intolerance, but rather a physiological response of the immune system after exposition to food components. Therefore, testing of IgG4 to foods is considered as irrelevant for the laboratory work-up of food allergy or intolerance and should not be performed in case of food-related complaints.

From the National Institute of Allergy and Infectious Diseases Guidelines for the Diagnosis and Management of Food Allergy in the United States [PDF]: Nonstandardized and Unproven Procedures; Guideline 12:

The (Expert Panel) recommends not using any of the following nonstandardized tests for the routine evaluation of IgE-mediated (food allergy):

  • Basophil histamine release/activation
  • Lymphocyte stimulation
  • Facial thermography
  • Gastric juice analysis
  • Endoscopic allergen provocation
  • Hair analysis
  • Applied kinesiology
  • Provocation neutralization
  • Allergen-specific IgG4
  • Cytotoxicity assays
  • Electrodermal test (Vega)
  • Mediator release assay (LEAP diet)

From the Australasian Society of Clinical Immunology and Allergy (ASCIA):

Inappropriate use of Conventional Testing: Food specific IgG, IgG4; Use: Diagnosis of food sensitivity / allergy.

Method: Antibodies to food are measured using standard laboratory techniques.

Evidence: Level II

Comment: IgG antibodies to food are commonly detectable in healthy adult patients and children, independent of the presence of absence of food-related symptoms. There is no credible evidence that measuring IgG antibodies is useful for diagnosing food allergy or intolerance, nor that IgG antibodies cause symptoms. In fact, IgG antibodies reflect exposure to allergen but not the presence of disease. The exception is that gliadin IgG antibodies are sometimes useful in monitoring adherence to a gluten-free diet patients with histologically confirmed coeliac disease. Otherwise, inappropriate use of food allergy testing  (or misinterpretation of results) in patients with inhalant allergy, for example, may lead to inappropriate and unnecessary dietary restrictions, with particular nutritional implications in children. Despite studies showing the uselessness of this technique, it continues to be promoted in the community, even for diagnosing disorders for which no evidence of immune system involvement exists.

From the Allergy Society of South Africa, Position Statement: ALCAT and IgG Allergy & Intolerance Tests [PDF]:

We are constantly consulted by colleagues, health funders and practitioners about the reliability and appropriateness of the ALCAT and IgG food allergy tests for patients with suspected allergies and other disorders. We would like to provide the following information to the readership of the journal and to the public.
The manufacturers and suppliers of ALCAT and the IgG test claim that the tests have diagnostic value in identifying substances responsible for allergic and intolerance reactions. These tests are being marketed directly to the public and health professionals, claiming to be more effective than traditional skin prick tests or serum specific IgE tests, particularly for delayed allergic reactions.  The manufacturers of the ALCAT test argue that orthodox allergy practice does not recognize delayed allergic reactions, when in fact these reactions are universally acknowledged to play a role in up to 30% of the spectrum of allergic reactions!
To date neither ALCAT nor IgG has been shown to have any predictive value in the diagnosis of allergy or intolerances.


The second test marketed with insufficient documentation is the IgG test for food allergies. Specific IgE determination and its diagnostic value have been documented for over three decades in being specific for allergic disorders. Although IgG does play a role in the allergic response, there is no evidence to suggest that it has a diagnostic value in predicting food allergens or other substances that may be affecting individuals. The IgG test is also marketed as effective in predicting foods implicated in Attention Deficit Disorder and obesity. There is no published evidence for these claims.

I also found review papers from immunologists and allergy experts:

From the Department of Pediatric Pneumology and Immunology, University Children’s Hospital Charité, Berlin: Unproven diagnostic procedures in IgE-mediated allergic diseases [PDF]:

The determination of specific IgG-antibodies in serum does not correspond with oral food challenges (5). In cow’s milk intolerance proved by oral challenge, no increased IgG-antibodies could be found (6). IgG milkspecific antibody levels are similar in children with early and late-type clinical reactions (7). Furthermore, there is no evidence that IgG subclasses (8) or the IgE/IgG4 antibody ratio (9) are reliable diagnostic tools. A study of 27 children with hen’s egg allergy found that children with a positive challenge tended to have a higher IgE/IgG 4 ratio and a higher IgG1/IgG4 ratio than those with anegative challenge test, but concluded that oral provocations are still necessary to confirm diagnosis of food allergy (10). A large study in 601 newborns, infants, children and adults showed that the determination of IgA and IgM antibodies did not contribute to the diagnosis of food allergy (11). Since IgG-antibodies to common dietary antigens can be detected in health and disease (12), the determination of food-specific IgG is of no clinical relevance (13) and should not be part of the diagnostic work-up of food allergy.

From the Department of Paediatrics, National University Hospital , Singapore, Diagnostic tests for food allergy [PDF]:

INAPPROPRIATE TESTS :Food-specific IgG tests
Tests for food-specific IgG are marketed as IgG radioallergosorbent tests and vary in offering measurements of total IgG toward a food, or IgG4 with or without food immune complex assay. The measurement of such specific IgG antibodies and their subclasses, primarily IgG4, is based on the fact that the titre falls after a period of withdrawal of the specific food antigen.
Thus, some physicians opt to use such a modality to diagnose food allergies. Unfortunately, the determination of specific IgG antibodies in serum does not correspond with oral food challenges.(43) Burks et al conducted a study of antibody responses to milk proteins in patients with milk-protein intolerance proved by oral challenge, and found that no increase in IgG antibodies was noted.(44) In another study, Shek et al concluded that foodspecific IgG or IgG4 does not add any information to the diagnostic workup of food allergy.(45) Furthermore, most people develop IgG antibodies to foods that they eat, and this is a normal immune response indicating exposure but not allergic sensitisation.(20) Recent studies have shown that the IgG response may even be protective, and thus prevents or protects against the development of IgE food allergy. Hence, there is no convincing evidence to suggest that this test has any diagnostic value for allergy.

Other reviews and commentary identified included the following:

From the UK House of Lords Science and Technology—Sixth Report on Allergy:

We are concerned both that the results of allergy self testing kits available to the public are being interpreted without the advice of appropriately trained healthcare personnel, and that the IgG food antibody test is being used to diagnose food intolerance in the absence of stringent scientific evidence. We recommend further research into the relevance of IgG antibodies in food intolerance, and with the establishment of more allergy centres, the necessary controlled clinical trials should be conducted. We urge general practitioners, pharmacists and charities not to endorse the use of these products until conclusive proof of their efficacy has been established.

From the Food Allergy Initiative:

IgG Testing: This test checks your blood for the presence of food-specific immunoglobulin G (IgG) antibodies. Unlike IgE antibodies, which occur in abnormally large quantities in people with allergies, IgG antibodies are found in both allergic and non-allergic people. Experts believe that the production of IgG antibodies is a normal response to eating food and that this test is not helpful in diagnosing a food allergy.

Interestingly, IgG tests are also rejected as unproven by at least one insurer, Aetna:

IgG RAST/ELISA Testing: There is no evidence that IgG antibodies are responsible for delayed allergic symptoms or intolerance to foods.

A consumer advocacy group investigated different allergy tests, including IgG, and noted the following:

Researchers from the consumer group trialled alternative tests that claim to diagnose food intolerances through analysis of blood samples or strands of hair, changes in electric current, or resistance to pressure applied to their legs or arms. They found that:

  • The tests diagnosed 183 intolerances – although the researchers actually had just one medically confirmed allergy and one food intolerance between them
  • Identical blood and hair samples sent under different names to the same company produced different test results
  •  There was little or no overlap between test results from different companies
  • The testers felt the practitioners applied more pressure when measuring resistance for certain foods – which they were then told to avoid
  • The tests recommended excluding up to 39 foods – which could make it difficult to eat a balanced diet and lead to nutritional problems.

The tests cost between £45 and £275 each, but an expert panel of medical specialists and a dietitian that assessed the results felt that none had diagnostic value for genuine allergies or intolerances.

The UK’s Advertising Standards Authority has evaluated the marketing of the YorkTest and the claim the test is clinically validated, and noted the following:

YorkTest provided three papers to support their claims for the FoodSCAN intolerance tests and believed those showed that the presence of IgG antibodies in the blood was indicative of food intolerances. however, we were concerned that the studies were conducted on people suffering from chronic medical conditions such as IBS and migraine and considered that those findings did not support a general claim for diagnosis of food intolerance. We noted one of the studies was published in an academic peer-reviewed journal, but also noted that although the study concluded that IgG tests may have a role in the treatment of irritable bowel syndrome symptoms, it did not refer to food intolerance among the general population and also stated that futher clinical research was required. We acknowledged that the independent charity Allergy UK endorsed YorkTest’s FoodSCAN range with one of their Consumer Awards but also noted this was based on anecdotal evidence (self-reporting) that individuals felt they were benefiting from using the tests. We concluded that the evidence submitted was not sufficiently robust to prove the efficacy of the tests for diagnosing food allergy or intolerance.

On this point, the ads breached CAP Code clauses 3.1 (Substantiation) 7.1 (Truthfulness) 50.1 (Health Beauty and Therapies)


At present, there are no reliable and validated clinical tests for the diagnosis of food intolerance. While intolerances are non-immune by definition, IgG testing is actively promoted for diagnosis, and to guide management. These tests lack both a sound scientific rationale and evidence of effectiveness. The lack of correlation between results and actual symptoms, and the risks resulting from unnecessary food avoidance, escalate the potential for harm from this test. Further, there is no published clinical evidence to support the use of IgG tests to determine the need for vitamins or supplements. In light of the lack of clinical relevance, and the potential for harm resulting from their use, allergy and immunology organizations worldwide advise against the use of IgG testing for food intolerance.




  • Scott Gavura, BScPhm, MBA, RPh is committed to improving the way medications are used, and examining the profession of pharmacy through the lens of science-based medicine. He has a professional interest is improving the cost-effective use of drugs at the population level. Scott holds a Bachelor of Science in Pharmacy degree, and a Master of Business Administration degree from the University of Toronto, and has completed a Accredited Canadian Hospital Pharmacy Residency Program. His professional background includes pharmacy work in both community and hospital settings. He is a registered pharmacist in Ontario, Canada. Scott has no conflicts of interest to disclose. Disclaimer: All views expressed by Scott are his personal views alone, and do not represent the opinions of any current or former employers, or any organizations that he may be affiliated with. All information is provided for discussion purposes only, and should not be used as a replacement for consultation with a licensed and accredited health professional.

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Posted by Scott Gavura

Scott Gavura, BScPhm, MBA, RPh is committed to improving the way medications are used, and examining the profession of pharmacy through the lens of science-based medicine. He has a professional interest is improving the cost-effective use of drugs at the population level. Scott holds a Bachelor of Science in Pharmacy degree, and a Master of Business Administration degree from the University of Toronto, and has completed a Accredited Canadian Hospital Pharmacy Residency Program. His professional background includes pharmacy work in both community and hospital settings. He is a registered pharmacist in Ontario, Canada. Scott has no conflicts of interest to disclose. Disclaimer: All views expressed by Scott are his personal views alone, and do not represent the opinions of any current or former employers, or any organizations that he may be affiliated with. All information is provided for discussion purposes only, and should not be used as a replacement for consultation with a licensed and accredited health professional.