SPT predictive values for the outcome of cashew challenges in children.

BACKGROUND: Cashew is a common cause of tree nut allergy in children. To date there have been few studies of diagnostic tests for cashew allergy, and positive predictive values (PPVs) for cashew as well as other tree nuts are largely extrapolated from studies of peanut allergy. How relevant these cut-offs are for cashew has not been formally explored. OBJECTIVE: We aimed to establish skin prick test (SPT) wheal sizes that correlated to 95% PPV for a positive food challenge for cashew. METHODS: We included all cashew oral food challenges (OFC) conducted as part of the HealthNuts (n=108, age 4-6 years) and SchoolNuts (n=37, age 10-14 years) studies, both recruited from the community (Population cohort). A second cohort of all cashew OFCs conducted at the Royal Children’s Hospital (RCH) allergy centre (n=343) (2011-2016) and a private allergy clinic based at RCH (n=43) was included via electronic medical record review (Clinic cohort). 95% PPV for cashew SPT was calculated for both cohorts. RESULTS: Among the population cohort (n=145), 62% of cashew OFC were positive compared to 20% of the clinic cohort (n=386). The SPT cut-off for 95% PPV derived from the population cohort was 10mm (95%CI 7.5-12.0). For the clinic cohort the 95% PPV was 14mm (95%CI 9.5-unknown). A SPT wheal size of 8mm had a PPV of 89% (95%CI 79-95) in the population cohort and 62% (95%CI 45-78) in the clinic cohort. CONCLUSION: A higher SPT wheal size may be more appropriate than the commonly used 8mm cut-off to guide clinical decisions around when to perform OFC for cashew.