Component Resolved Diagnostics Roisin Fitzsimons Consultant Nurse Guy’s and St Thomas NHS Foundation Trust
Overview of session Current diagnostic methods What is component resolved diagnostics (CRD)? Application to practice
Allergy Diagnosis History Skin Prick Testing (SPT) Specific IgE Testing (SpIgE) Provocation - Oral food challenge
What is CRD?
Protein Formation
Major peanut allergens Peanut components Ara h 2 Ara h 1 Ara h 8 Ara h 9 Ara h 3 Major peanut allergens
Features of peanut components Seed storage proteins PR10 proteins Lipid Transfer Proteins (LTP) Ara h 1,2,3 - major peanut allergens Ara h 8 Ara h 9 Responsible for primary sensitisation Recognition of similar structures Found in nuts, seeds, legumes Bet v 1 homologue (Apple Mal d 1) Heat resistant and stable May cause systemic, severe reactions Altered by heating/gastric juices Risk of severe reactions Not easily broken down Localised symptoms Cross-reactivity with Pru p 3 Present in large quantities Pollen food syndrome Common in Southern European countries Can we predict severity of allergy? Formed of components Structure and significance varies
Relevance to practice Can we predict severity of a reaction? Ara h 1,2,3 – primary sensitisation to peanut Ara h 8 – cross reactivity with Birch pollen
Case study - Rose 8 year old Sesame allergic Allergic Rhinitis FH peanut allergy Always avoided peanuts Immunological investigations SPT 2mm SpIgE 4.38ku/ml Ara h 1 – 0.00 Ara h 2 – 0.16 Ara h 3 – 0.00 Ara h 8 – 6.24
What next? Allergic; avoid peanuts? Tolerant; introduce peanuts? Probably OAS; introduce peanuts with caution? Not sure; OFC?
Proceeded to OFC Tolerated first two doses Third dose – oral pruritus, no objective symptoms Repeated dose – worsening of pruritus, not distractible What next?
Implications for practice Ara h 2 clinically relevant for predicting positive OFC Presence of Ara h 1&3 increases likelihood of allergy Ara h 8 may suggest OAS Listen to your patient and family
Summary CRD useful in aiding diagnosis Should not replace clinical history and holistic evaluation Easier to predict allergy than tolerance
Reference list Beyer K et al 2015, Allergy; 70: 90–98. Dang T D et al, 2012, J Allergy Clin Immunol;129:1056-63 Nicolaou N et al, 2010, J Allergy Clin Immunol; 125:191-7 Asarnoj A and Movérare R et al, 2010, Allergy