Overview
Definition:
An oral food challenge (OFC) is the gold standard diagnostic test for food allergy, involving the supervised, graded administration of a suspected food allergen to a patient to assess for clinical reactivity.
Epidemiology:
Food allergies affect 5-8% of children, with OFCs used when diagnosis is uncertain or to assess tolerance after a period of avoidance or treatment
Common allergens include milk, egg, peanut, soy, wheat, tree nuts, fish, and shellfish.
Clinical Significance:
Accurate diagnosis of food allergy is crucial for preventing severe anaphylactic reactions, improving quality of life, and avoiding unnecessary dietary restrictions
OFCs provide definitive diagnosis when clinical history and other tests are inconclusive.
Indications For Challenge
Uncertain Allergy Diagnosis:
When history is suggestive but skin prick tests (SPT) or specific IgE levels are borderline or discordant with clinical symptoms.
Assessment Of Tolerance:
To determine if tolerance has developed in children previously diagnosed with a food allergy and who have undergone a period of strict avoidance.
Research Protocols:
In clinical trials investigating new therapies or diagnostic methods for food allergy.
Confirmation Of Diagnosis:
To confirm a clinical suspicion of food allergy in a controlled environment before recommending strict avoidance.
Safety Protocols Pre Challenge
Patient Selection:
Careful assessment of patient history for previous severe reactions, comorbidities like asthma (poorly controlled), and adherence to instructions.
Informed Consent:
Detailed discussion with parents/guardians about the procedure, risks (including anaphylaxis), benefits, and alternative diagnostic methods.
Facility Readiness:
Ensuring the clinic is equipped for managing anaphylaxis, including readily available epinephrine auto-injectors, oxygen, intravenous fluids, and resuscitation equipment.
Staff Training:
All staff involved must be trained in recognizing and managing anaphylaxis, including administration of epinephrine and basic life support.
Scheduling:
Ideally performed in the morning, allowing sufficient time for observation and avoiding weekends or evenings when emergency support may be limited.
Safety Protocols During Challenge
Graded Dosing:
Administering increasing doses of the food allergen at defined intervals, starting with a very small amount (e.g., 1mg or less for solids, 1-10mL for liquids).
Observation Period:
Monitoring the patient closely for signs and symptoms of allergic reaction after each dose
A typical observation period post-final dose is 2-3 hours, but can extend up to 4-6 hours depending on the allergen and protocol.
Symptom Recognition:
Vigilance for cutaneous (urticaria, angioedema), respiratory (wheezing, stridor, cough), gastrointestinal (vomiting, diarrhea, abdominal pain), and cardiovascular (hypotension, pallor, lethargy) symptoms.
Escalation Of Care:
Immediate cessation of the challenge and prompt treatment of any allergic reaction, starting with epinephrine if moderate to severe symptoms develop.
Controlled Environment:
Ensuring the patient remains in a supervised area throughout the challenge and observation period.
Safety Protocols Post Challenge
Discharge Criteria:
Patient is symptom-free, vital signs are stable, and there is no evidence of delayed reactions
Parents should be educated on signs of delayed reactions.
Follow Up Instructions:
Clear instructions on when to seek immediate medical attention if symptoms recur or new symptoms appear after discharge, including signs of delayed anaphylaxis.
Documentation:
Detailed recording of the entire procedure, including doses given, time intervals, observed symptoms, interventions, and patient response.
Allergen Introduction:
If the challenge is negative and tolerance is established, advise parents to regularly include the food in the child's diet to maintain tolerance.
Management Of Reactions
Mild Reactions:
Antihistamines (e.g., Cetirizine 0.5-1mg/kg/dose, max 10mg orally or IV)
Close monitoring for progression.
Moderate To Severe Reactions Anaphylaxis:
Immediate intramuscular epinephrine (0.01 mg/kg, max 0.3-0.5 mg depending on age)
Call for emergency medical services
Oxygen therapy
Intravenous fluids if hypotensive
Corticosteroids and H2 blockers may be considered as adjuncts.
Anaphylaxis Protocol:
Adherence to established anaphylaxis management algorithms, including repeat epinephrine doses if necessary and continuous monitoring.
Key Points
Exam Focus:
The OFC is the gold standard
anaphylaxis management is paramount
Know the graded dosing and observation times.
Clinical Pearls:
Always have epinephrine readily accessible
Consider comorbidities, especially asthma
Educate parents thoroughly on risks and home management.
Common Mistakes:
Performing OFCs in inadequately equipped facilities or without trained staff
Inadequate observation periods
Poorly controlled asthma patients undergoing challenges
Underestimating the risk of delayed reactions.