Background: There are few reports on oral food challenge (OFC) tests of walnut.
Objective: The purpose of this study is to clarify the risk factors predicting positive result in walnut OFC.
Subjects: We retrospectively analyzed 68 patients who had undergone walnut OFC from May 2006 to August 2014 at Sagamihara National hospital.
Methods: Open OFCs were performed with greater than 3g of walnut. We measured all patients’ walnut specific IgE within 1 year of their OFCs. Furthermore, we also randomly measured 33 subjects’ allergen components (eg. Jug r 1, Jug r 3) of total subjects. We judged as positive when patients had obvious objective symptoms. When their symptoms at walnut OFC were uncertain, we encouraged them to take same quantity of walnut at home. We made the final conclusion by checking reproducibility at next visit at outpatients.
Results: Among 68 patients, 49 patients were males. Median of the patient’s age was 7.1(range; 3.1-22.4) years old. Reasons for elimination of walnut were as follows; 1) positive for specific IgE (n=37, 54%), 2) history of immediate reactions to walnut (n=23, 34%), 3) anxiety etc. (n=8, 12%). Forty eight patients (71%) had atopic dermatitis, 30 patients (44%) asthma, 31 patients (46%) allergic rhinitis, 13 patients (19%) allergic conjunctivitis. Twenty four patients (35%) had history of immediate reaction to peanut, and 8 patients (12%) had history of immediate reaction to other nuts. OFC was positive in 34 patients (50%). Five patients (7%) experienced anaphylaxis. Twenty four cases (71%) had cutaneous symptoms, 16 cases (47%) respiratory symptoms, 10 cases (29%) gastrointestinal symptoms, 6 cases (18%) mucosal symptoms, 4 cases (12%) neurological symptoms. Twenty five patients (74%) were treated with antihistamine, 11 patients (32%) with 2 stimulant inhalation, 4 patients (12%) with steroid drug, 3 patients (9%) with adrenaline. Comparing positive patients and negative patients in OFC, positive patients had more frequent history of immediate reaction to walnut (50% vs 18%, p=0.0096). The walnut specific IgE titers in positive were higher than those in negative (median of specific IgE 3.36 UA/ml vs 0.47 UA/ml, p=0.0013). Twelve of 14 patients (67%) positive to Jug r 1 were positive in OFC.
Conclusions: Healthcare providers should be prepared for high positive reaction in walnut OFC, possibly anaphylaxis. Risk factors predicting positive reactions in walnut OFC are the past history of immediate reactions to walnut and high titer of walnut specific IgE, positive to Jug r 1.