Ajax Harwood Clinic
Food sensitivity testing: should I be tested?
Food allergy (IgE-mediated)
Defined testing criteriaAlso called: food allergy, IgE food allergy, anaphylaxis (food), true food allergy
Patients or parents raise food allergy after a reaction, or want testing after reading about 'food sensitivity' panels and wanting to know the difference. This section describes what a real, validated food allergy work-up looks like, in contrast to the unvalidated 'sensitivity' testing covered elsewhere on this page.
Raises suspicion
- • Hives, lip or facial swelling, wheeze, vomiting, or throat tightness within minutes to about two hours of eating a specific food
- • A reaction reproducible on more than one exposure to the same food
- • Anaphylaxis: rapid-onset symptoms involving more than one body system (skin plus breathing, or skin plus circulation)
- • Infant eczema that is difficult to control, which raises the pretest probability of a co-existing food allergy
Does not raise suspicion
- • Bloating, fatigue, brain fog, or joint pain hours to days after eating, with no hives, swelling, or breathing symptoms: this pattern does not fit IgE-mediated allergy and is not an indication for allergy testing
- • Feeling 'better' avoiding a food without ever having had an acute reaction to it
Red flags
- • Facial or throat swelling, wheeze, widespread hives, dizziness, or fainting shortly after eating: this is possible anaphylaxis; call 911 or attend the nearest emergency department, and an epinephrine auto-injector should be prescribed and carried after any such reaction
Who to test
- History suggestive of IgE-mediated reaction to a specific, identifiable foodSkin-prick testing or serum specific IgE to the specific suspected food (no TestSelect entry; allergist-directed), guided by history, not a broad panel
- Diagnosis remains uncertain after history and specific IgE or skin testingOral food challenge (no TestSelect entry; allergist-directed, in a monitored setting) is the diagnostic gold standard
More likely instead
Counselling script
“If you've had hives, swelling, or trouble breathing after a specific food, testing that food with a skin or blood test, guided by your history, is the right next step, and if it's happened before we should also talk about carrying an epinephrine auto-injector. Without that kind of reaction, a broad allergy panel usually creates more confusion than answers, since it can flag foods you tolerate fine. Where a food stays uncertain, a supervised oral food challenge is the most reliable way to settle it.”
Chart snippet (OSCAR-safe plain text)
Concern discussed, not tested
Concern re: food allergy discussed, raised by patient or after a reaction. Discriminating features: hives, swelling, wheeze, or throat tightness after a specific food; reviewed. Assessment: history consistent with possible IgE-mediated food allergy to a specific food. Plan: allergy referral for history-guided specific IgE or skin-prick testing; epinephrine auto-injector prescribed if a reaction has occurred. Ref: Choosing Wisely Canada allergy and immunology recommendations 2025; ASCIA oral food challenge position paper 2024. Patient given info page: https://food-sensitivity.ajaxharwoodclinic.com/patient Revisit if: a reaction recurs, or a new food becomes suspect.
Testing ordered
Concern re: food allergy discussed. Discriminating features: reaction pattern consistent with IgE-mediated allergy to an identified food. Assessment: specific IgE or skin-prick testing indicated, guided by history. Plan: allergist referral for testing of the specific suspected food; broad panel testing not ordered. Ref: Choosing Wisely Canada allergy and immunology recommendations 2025. Patient given info page: https://food-sensitivity.ajaxharwoodclinic.com/patient Revisit if: results are ambiguous and an oral food challenge is being considered.
Revisit if
- • A reaction recurs or worsens
- • A new food becomes suspect
- • Epinephrine auto-injector expires or is used
References
- 1. Canadian Society of Allergy and Clinical Immunology / Choosing Wisely Canada. Allergy & Clinical Immunology: Eight Tests and Treatments to Question (2025)Don't order specific IgE tests unless indicated by the patient's clinical history specific to that food
- 2. Canadian Society of Clinical Chemists / Choosing Wisely Canada. Clinical Biochemistry recommendations (2025)Allergen-specific IgE testing should be correlated to specific exposures from the history, not ordered as a panel
- 3. Australasian Society of Clinical Immunology and Allergy (ASCIA). Position Paper: Oral Food Allergen Challenges (2024)Oral food allergen challenges are the diagnostic gold standard for food allergy
Evidence notes
Tag rationale: A, not borderline; IgE-mediated food allergy has well-defined diagnostic criteria (history plus specific IgE/skin testing, confirmed by oral challenge where needed). A Canadian-authored CMAJ review (Abrams and Sicherer, 'Diagnosis and management of food allergy,' CMAJ 2016, PMID 27601605) was located as a strong Canadian source for the oral-challenge-as-gold-standard claim, but its full text could not be fetched within this session (CMAJ and Europe PMC both blocked automated retrieval); ASCIA (international) is used instead for that specific claim, and is flagged as a substitute pending a working Canadian citation. Resolved 2026-09-23: Dr. Yu approved this page structure (decision 4).
Mast cell activation syndrome (MCAS)
Defined testing criteriaAlso called: mast cell activation syndrome, MCAS, mast cell disorder, histamine and mast cell issues
MCAS is increasingly discussed on social media and by some NDs as an explanation for a wide constellation of symptoms, often alongside 'histamine intolerance' and hypermobility. True MCAS is a recognized but genuinely rare diagnosis with strict consensus criteria; it is frequently suspected far more often than it is confirmed, because its individual symptoms overlap heavily with common, more likely conditions.
Raises suspicion
- • Recurrent episodes of flushing, hives, abdominal cramping, diarrhea, low blood pressure, or near-fainting, occurring together in the same episode
- • Episodes that involve more than one organ system at once (for example, skin plus GI plus cardiovascular) and are triggered by a recognizable stimulus
- • Symptoms that improve with mast cell-stabilizing or antihistamine-type medication
- • A rise in serum tryptase during a reaction compared to the patient's own baseline
Does not raise suspicion
- • Chronic fatigue, brain fog, or anxiety alone, without discrete, recurrent, multi-system episodes
- • A single vague symptom attributed to 'histamine' or 'mast cells' without an episodic, reproducible pattern
Red flags
- • Facial or throat swelling, wheeze, or fainting during an episode: treat as possible anaphylaxis (call 911 or attend the nearest emergency department) regardless of whether MCAS is eventually confirmed
Who to test
- Recurrent, multi-system episodes consistent with mast cell activationSerum tryptase (no TestSelect entry; specialist-directed), ideally both at baseline and within hours of a reaction, is the key test; a single normal tryptase does not exclude MCAS but a documented rise supports it
More likely instead
- • Histamine intolerance
- • Food allergy (IgE-mediated) (if a specific food reliably triggers episodes)
- • Depression
- • IBS
- • Postural orthostatic tachycardia syndrome (POTS) (if fainting or lightheadedness on standing is prominent)
Counselling script
“If you're having recurrent episodes that involve more than one body system at once, like skin, gut, and blood pressure symptoms together, and they respond to mast cell medications, MCAS is worth formally assessing with a specialist. Without that clear, episodic, multi-system pattern, it's more likely that a few of your symptoms are overlapping with a more common condition. Because MCAS has strict diagnostic criteria and is genuinely rare, this diagnosis should be made carefully rather than assumed.”
Chart snippet (OSCAR-safe plain text)
Concern discussed, not tested
Concern re: mast cell activation syndrome (MCAS) discussed, raised by patient or after online research. Discriminating features: recurrent multi-system episodes, trigger pattern, response to mast cell medication; reviewed. Assessment: features reviewed against consensus criteria; overlap with more common conditions considered. Plan: allergy/immunology referral for tryptase testing during a future episode if pattern is convincing. Ref: Valent et al. MCAS diagnostic consensus 2020. Patient given info page: https://food-sensitivity.ajaxharwoodclinic.com/patient Revisit if: a clear episodic, multi-system pattern emerges, or anaphylaxis features occur.
Testing ordered
Concern re: MCAS discussed. Discriminating features: recurrent, multi-system episodes with a plausible trigger present. Assessment: specialist-directed serum tryptase testing indicated around a future episode. Plan: baseline tryptase and specialist referral arranged; patient counselled to seek tryptase testing within hours of the next episode if possible. Ref: Valent et al. MCAS diagnostic consensus 2020. Patient given info page: https://food-sensitivity.ajaxharwoodclinic.com/patient Revisit if: tryptase rises with a reaction, or symptoms do not fit the pattern on further review.
Revisit if
- • A clear episodic, multi-system pattern becomes evident
- • Anaphylaxis features occur during any episode
- • Specialist assessment is pending
References
- 1. International Journal of Molecular Sciences (Valent et al., ECNM/AIM consortium authors). Diagnosis, Classification and Management of Mast Cell Activation Syndromes (MCAS) in the Era of Personalized Medicine (2020)Consensus diagnostic criteria requiring recurrent, multi-system symptoms responsive to mast cell-targeted therapy, and caution that overlapping symptoms are often confused with MCAS when only clinical criteria are applied without biochemical confirmation
Evidence notes
Tag rationale: A, not borderline as a diagnostic category (strict consensus criteria exist, [1]), but clinically the tag needs a caution attached: MCAS is a real but rare and frequently over-suspected diagnosis, since its component symptoms overlap with many common conditions ([1] itself flags this overlap problem). A dedicated AAAAI or ECNM patient-facing statement specifically on over-diagnosis was sought but not separately located within this session's budget; the overlap/over-application caution is instead drawn directly from the Valent 2020 consensus paper's own text, which is authored by core ECNM/AIM consortium members, so it is treated as adequately sourcing that caution rather than left as an unsourced gap.
Popular labels: what they mean
"Food sensitivity" (IgG/IgG4 panel result)
Not a recognized medical diagnosisAlso called: food sensitivity, food intolerance test result, IgG food panel, IgG4 food panel, ALCAT test
Patients bring in a report, often from an ND, showing a long list of foods they are 'sensitive' or 'intolerant' to, based on an IgG or IgG4 blood panel (or a leukocyte-reactivity test such as ALCAT). The report looks precise and medical, and the symptoms that prompted the test are usually real; the panel itself does not validly explain them.
Raises suspicion
- • This label itself has no discriminating features, because IgG/IgG4 antibodies to food are a normal marker of exposure, found in symptomatic and asymptomatic people alike. If the history instead suggests hives, swelling, or a rapid reaction to a specific food, that points to the Food allergy (IgE-mediated) page instead.
Does not raise suspicion
- • A long list of 'reactive' foods on an IgG or IgG4 panel
- • Bloating, fatigue, brain fog, or joint aches attributed to the panel result
- • Feeling somewhat better after cutting out the flagged foods, which can reflect a placebo effect, coincidental FODMAP reduction, or simply eating more mindfully
Red flags
- • None specific to this label. If true allergy features (hives, swelling, wheeze) are present, redirect to the Food allergy (IgE-mediated) page.
Who to test
- Everyone presenting with this concernNo IgG or IgG4 food panel, and no leukocyte-reactivity test such as ALCAT, has validated clinical use for diagnosing food sensitivity or guiding elimination diets. If a true IgE-mediated allergy is suspected from the history, history-guided specific IgE or skin testing is the appropriate test instead (see Food allergy (IgE-mediated)).
More likely instead
- • IBS
- • FODMAP sensitivity
- • Acid reflux
- • lactose intolerance
- • Celiac disease (if not yet excluded)
- • Food allergy (IgE-mediated) (if the history suggests a true IgE-mediated reaction)
Counselling script
“IgG and IgG4 antibodies to food are a normal sign your immune system has seen that food before, not evidence of a problem with it, so this panel isn't a validated way to diagnose food sensitivity. Your symptoms are real, and we should still look for what's actually causing them. If your history points to a true allergy instead, that's tested differently, and worth doing properly.”
Chart snippet (OSCAR-safe plain text)
Concern discussed, not tested
Concern re: 'food sensitivity' discussed, raised after an ND-ordered IgG or IgG4 food panel. Discriminating features for true IgE-mediated food allergy: absent. Assessment: IgG/IgG4 food antibody panel is not a validated diagnostic test; result reflects food exposure, not sensitivity or intolerance. Plan: no further IgG-based testing ordered; alternative causes of symptoms discussed; Food allergy (IgE-mediated) pathway offered if history warrants. Ref: CSACI position statement on IgG food testing 2012; Choosing Wisely Canada allergy and immunology recommendations 2025. Patient given info page: https://food-sensitivity.ajaxharwoodclinic.com/patient Revisit if: features of true IgE-mediated food allergy develop.
Revisit if
- • Hives, swelling, wheeze, or another feature of true food allergy develops
- • Symptoms persist despite elimination based on the panel: reassess for the real underlying cause
References
- 1. Canadian Society of Allergy and Clinical Immunology. CSACI Position statement on the testing of food-specific IgG (2012)— older guidelineNo body of research supports using IgG food antibody testing to diagnose adverse reactions to food
- 2. Canadian Society of Allergy and Clinical Immunology / Choosing Wisely Canada. Allergy & Clinical Immunology: Eight Tests and Treatments to Question (2025)Don't order specific IgG testing to panels of foods
Evidence notes
Tag rationale: C, not borderline. CSACI [1] and Choosing Wisely Canada [2] both reject IgG/IgG4 food panels as a diagnostic tool; [1] is flagged older_than_10y (2012) but its conclusion is reaffirmed by the current (2025) Choosing Wisely Canada recommendation, so it is not treated as stale. ALCAT is grouped here on the basis of identical marketed indication, consistent with how the linked "Food sensitivity" (IgG/IgG4 panel result) test record treats it; no separately stronger evidence base for ALCAT was located in this session.
Histamine intolerance
Not a recognized medical diagnosisAlso called: histamine intolerance, HIT, histamine sensitivity, DAO deficiency
Patients raise histamine intolerance after reading that symptoms following high-histamine foods (aged cheese, wine, cured meats, leftovers) reflect an inability to break down dietary histamine, often via reduced DAO (diamine oxidase) enzyme activity. The symptom pattern is genuine and reported reproducibly by many patients; a validated diagnostic test for the underlying claim does not currently exist.
Raises suspicion
- • This label itself has no validated discriminating features or confirmatory test. A reproducible symptom pattern tied to high-histamine foods, improving on a trial low-histamine diet, is the best available clinical signal, not a specific finding on any blood test.
Does not raise suspicion
- • A low serum or plasma DAO activity result: this has also been found in people without symptoms, and does not reliably predict who has histamine intolerance
- • Flushing, headache, or GI upset after high-histamine foods, on its own, without a documented reproducible pattern
Red flags
- • Facial or throat swelling, wheeze, or fainting after a specific food: this suggests true food allergy or MCAS, not histamine intolerance; assess urgently
Who to test
- Everyone presenting with this concernNo blood test, including DAO activity, has validated clinical use for diagnosing histamine intolerance. A structured, dietitian-guided low-histamine diet trial with reintroduction is the most defensible way to assess the pattern clinically.
More likely instead
- • Mast cell activation syndrome (MCAS) (if episodes are multi-system and recurrent, not just food-triggered)
- • Food allergy (IgE-mediated) (if a specific reaction is rapid and involves hives or swelling)
- • IBS
- • Acid reflux
- • medication effects (some medications reduce DAO activity or interact with dietary amines)
Counselling script
“Reacting to high-histamine foods like aged cheese or wine is a pattern many people describe, but no blood test, including DAO, reliably diagnoses it. If this fits you, a supervised trial of a lower-histamine diet with a planned reintroduction is the most honest way to see if it explains your symptoms. Reactions with swelling, wheeze or fainting are different and need urgent assessment.”
Chart snippet (OSCAR-safe plain text)
Concern discussed, not tested
Concern re: histamine intolerance discussed, raised by patient or ND. Discriminating features for food allergy or MCAS: absent. Assessment: histamine intolerance has no validated diagnostic test; DAO activity testing does not reliably distinguish affected from unaffected individuals. Plan: no DAO or histamine testing ordered; structured low-histamine diet trial with reintroduction discussed, dietitian referral considered. Ref: Hrubisko et al. histamine intolerance review 2021. Patient given info page: https://food-sensitivity.ajaxharwoodclinic.com/patient Revisit if: symptoms do not track with the diet trial, or features of true food allergy or MCAS develop.
Revisit if
- • Symptoms do not clearly track with a structured diet trial
- • Multi-system, recurrent episodes emerge, suggesting MCAS
- • Features of true food allergy develop
References
- 1. Nutrients (Hrubisko et al.). Histamine Intolerance-The More We Know the Less We Know. A Review (2021)Review describing the inconsistency and variety of histamine intolerance manifestations, and that reduced DAO activity is also found in healthy individuals, limiting its use as a diagnostic marker
Evidence notes
Tag rationale: C, kept as instructed by the brief. This is genuinely borderline: histamine intolerance has a plausible mechanism (dietary histamine plus reduced DAO clearance) and Hrubisko 2021 treats a low-histamine diet response as the practical marker of the condition, which has some B-like features (a real condition worked up clinically, just without a lab test). It is kept at C here because, unlike NCGS or SIBO, there is no expert consensus diagnostic protocol (no equivalent of a Salerno-type criteria document) and no validated laboratory test exists at all, including in specialist practice; the diagnosis is closer to a working hypothesis than an accepted clinical entity. Flagging for physician review given the borderline case.
General clinical reference for Ajax Harwood Clinic. Not medical advice, and not a substitute for individualized clinical assessment.