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!