Diagnosing food allergy - CYANS...Diagnosing food allergy Advances, pitfalls and problems Rosie Hague Consultant in Paediatric Allergy, Immunology and Infectious Diseases RHSC YorkhillTypes
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Diagnosing food allergy Advances, pitfalls and problems
Rosie Hague
Consultant in Paediatric Allergy, Immunology and Infectious Diseases
RHSC Yorkhill
Conditions attributed to food allergy
l 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
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
l 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
Symptoms associated with IgE mediated allergic reactions
l 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
Anaphylaxis?
l Urticaria l Angioedema l Acute wheeze l Acute stridor l Shock
Non IgE mediated allergy
l 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
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)
Chronic Urticaria > 6 weeks duration Regular episodes. May have associated urticaria in response to physical stimuli (dermographism, pressure, cold, heat)
Allergen not identified
Refer to Consultant Dermatologist if:
• Persistent> 3 months • Unresponsive to 3 different
antihistamines each for 4-6 weeks • Additional symptoms or bruising
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
Allergen identified: Give interim avoidance advice, an allergy management plan (including chlorpheniramine)
and refer to allergy clinic
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 <1year l Antihistamine use l Not possible in severe eczema l Hard to interpret small wheals l Occasional anaphylaxis
Serological tests (ImmunoCap)
l measures specific IgE l safe l not influenced by antihistamine l high values correlate reasonably
well with risk of type 1 reactions
Problems of specific IgE tests
l Very accessible l “food mix” l Too tempting to ask for lots! l Difficult to intepret in children with very high
total IgE l Titre does not correlate with severity of reaction l Testing without history l Cost
Oral provocation test
l “Gold standard” l Cannula if previous
severe acute reaction l Apply to skin l Apply to lips l Ingest increasing
amounts
Problems in oral challenge
l Use of open method when symptoms subjective l Insufficient observation to detect delayed
reactions l Inappropriate formulation of test food l False negative in food related exercise induced
anaphylaxis l Labour/resource intensive
Are there any advances?
Component testing
Allergenic components of peanuts
Component Protein tye comments
Ara H 1 Storage protein Peanut specific marker
Ara H2 Storage protein Peanut specific marker
Ara H3 Storage protein Peanut specific marker
Ara H5 Profilin Marker of grass pollen cross reactivity
Ara H6 Storage protein Similar to ara H2
Ara H8 PR10 protein Marker of birch pollen cross reactivity
Ara H9 Ns LTP Marker of peach cross reactivity
What about eggs?
l Ovomucoid l Heat stable
l Ovalbumin l Conalbumin l Lysozyme
What you get
The problem of idiopathic anaphylaxis
l History still essential l Don’t forget exercise
induced! l 20% diagnosis
assisted with ISAC l wheat l nut l lupin
Pitfall number 4
Getting an answer to a question you never asked!
Take home message
l Make a clinical diagnosis first! l Decide what the question is before deciding on
the test l Pick the right test and know how to interprete
it. l Never do a test which will not influence
management l Never do a test if you don’t want the result!
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