Diagnosing food allergy Advances, pitfalls and problems

Rosie Hague Consultant in Paediatric Allergy, Immunology and Infectious Diseases RHSC Yorkhill

Conditions attributed to food allergy Anaphylaxis l  Urticaria l  Eczema l  Gastro-oesophageal reflux l  Vomiting l  Colic l  Diarrhoea l  Constipation l 

Abdominal pain l  Irritable bowel l  Depression l  Autism l  Glue ear (catarrh) l  Chronic fatigue l  Hyperactivity l 

Pitfall number 1 Taking the label of “allergy” at face value

Types of adverse reaction to foods l  IgE

mediated immune reactions l  Non-IgE mediated immune reactions l  Non-allergic food intolerance l  Pharmacological l  Metabolic l  Toxic

l  Food

aversion

A careful history is the best tool in the diagnosis of allergy

The history l  Nature

and duration of symptoms l  Possible precipitants, and timescale l  Previous exposure to possible precipitant l  Previous reactions l  Tolerance of/exposure to related allergens l  What foods avoiding and why

History of atopy l  Asthma l  Eczema l  Hay

fever l  Contact dermatitis l  Drug reactions l  Family

history

Symptoms associated with IgE mediated allergic reactions Rash l  Itch l  Sneezing l  Swollen lips l  Metallic taste in mouth l 

Hoarse voice l  Lump in the throat l  Wheezing l  Nausea and vomiting l  Abdominal cramps l 

Symptoms associated with IgE mediated allergic reactions Rash l  Itch l  Sneezing l  Swollen lips l  Metallic taste in mouth l 

Hoarse voice l  Lump in the throat l  Wheezing l  Nausea and vomiting l  Abdominal cramps l 

Anaphylaxis? l  Urticaria l  Angioedema l  Acute

wheeze l  Acute stridor l  Shock

Non IgE mediated allergy Itch l  Erythema l  Atopic eczema l 

Pallor and tiredness l  Growth faltering with 1 or more GI symptoms l 

GO reflux disease l  Loose/frequent stools l  Blood/mucous in stools l  Abdominal pain/colic l  Food refusal/aversion l  Constipation l  Peri-anal redness l 

These are probably not allergy l  Urticaria

with no obvious precipitant l  Peri-oral/contact erythema l  Isolated behavioural disturbance l  Chronic GI symptoms unresponsive to dietary manipulation

Acute Urticaria < 6 weeks duration

Detailed history may identify trigger e.g drug reaction, viral illness (urticaria days to weeks) or food allergy (urticaria hours)

Allergen identified: Give interim avoidance advice, an allergy management plan (including chlorpheniramine) and refer to allergy clinic

Allergen not identified

Test rarely required unless evidence of systemic disease or history of additional symptoms or signs such as bruising (suggesting urticarial vasculitis) or joint swelling

Usually autoimmune. Occasionally occurs in association with underlying infection or as part of autoinflammatory syndrome (when presenting in early childhood with associated pyrexia, malaise and joint or abdominal pain) May be associated with other autoimmune conditions such as thyroid disease.

Management: Chlorpheniramine if < 6 months Long acting antihistamine if > 6 months e.g fexofenadine, cetirizine, loratadine Sedative anti-histamine at night if sleep disturbed

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Chronic Urticaria > 6 weeks duration Regular episodes. May have associated urticaria in response to physical stimuli (dermographism, pressure, cold, heat)

Refer to Consultant Dermatologist if: • Persistent> 3 months • Unresponsive to 3 different antihistamines each for 4-6 weeks • Additional symptoms or bruising

Pitfall number 2 Testing before engaging brain!

If the clinical picture is not of IgE mediated disease, don’t do IgE based tests!

Trial of elimination l  Eliminate

suspected food for 2-6 weeks l  Symptom diary before during and after l  Re-introduce after trial

IgE based tests

Pitfall number 3 Asking the wrong question of the test

Rosie’s laws l  Never

do a test if you don’t want the results! l  Don’t do a test without a supportive history l  Don’t do a test which won’t alter management

Skin prick testing l  Rapid l  Cheap l  Result

on the day l  Correlate well with type I symptoms

Problems of skin prick testing l  Less

useful in