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Diagnosis of IgE mediated food allergy (Skin Prick Test (SPT) (Methods (A…
Diagnosis of IgE mediated food allergy
Who by?
Paediatric allergist
DTN's role in diagnosis
To assist paediatric allergist by:
Provide dietetic support for oral food allergen challenges
Supervise restricted diets to optimise growth
Obtain detailed allergy-focused diet hx
Referral to paed if allergy is suspected
Skin Prick Test (SPT)
Not useful for:
Non IgE mediated food allergy
Nonspecific rash
Food intolerances
Behavioural disorders
Methods
A postive control (histamine) and a negative control (50% glycerol must be used
Antihistamines must be ceased 48hrs prior to SPT
Allergen extracts are aqueous solutions of proteins with 50% glycerol
A droplet is placed on the skin and a lancet pricked through it into skin
Results are recorded as size of wheal produced
Useful for:
Rhinitis or allergic conjuctivitis
Anaphylaxis
Asthma
Eczema or atopic dermatitis
Interpretation of results
SPT is considered positive if its larger than the negative control by:
at least 3mm in children >2yrs
at least 2mm in children <2yrs
Negative SPT excludes IgE allergy (>95% specific) can reintroduce those foods
Positive sSIgE and SPT
Must exclude the food and reintroduce to confirm
Indicates with about 50% accuracy that pt has true IgE-mediated food allergy
Serum specific IgE
Blood test that measures food specific IgE in the serum
If positive needs further investigations (eg SPT) as not 100% conclusive
Indicates sensitisation not allergy
Measures total IgE and is often stated as a group of foods eg milk, nuts, eggs
Must be used in conjunction with clinical history
Can be used when no allergy service (eg at GP)
89% of pts diagnosed by sSIgE alone were able to reintroduce food into their diet after an oral challenge
Dietary exclusion & reintroduction to confirm IgE mediated food allergy
Situations when home reintroduction not recommended
History of anaphylaxis
SPT wheal is over 6mm
Reintroduction phase
Once symptoms are resolved, suspected foods are reintroduced, one a time, while maintaining a food and symptom diary
Exclusion phase
When a food has been identified as +ve on SPT, it must be removed from diet until symptoms resolve