Background: We previously devised an algorithm utilizing skin prick tests (SPT), basophil activation tests (BAT) and co-allergy status to reduce the need for oral food challenges (OFC) in 63 patients with suspected walnut/pecan allergies. Objective: To validate prospectively the NUT CRACKER diagnostic algorithm in a new cohort of patients (n=120) and to study the utility of SPT and BAT in predicting walnut-pecan allergy severity in both groups (n=183). Methods: Patients (n=183) aged 8 (6-11) years, median, (IQR) with suspected tree nut allergy were studied. SPT utilized ground nut extract (10 mg/ml) and BAT assessed allergen-induced basophil CD63 expression. Allergy was determined based on a recent reaction or a positive oral food challenge (OFC) and tolerance was defined by regular consumption or a negative OFC. Results: Walnut BAT was significantly higher in walnut/pecan dual compared to single walnut allergy (p=0.003) and predicted the need for epinephrine during positive walnut OFCs (p=0.009). Results of walnut and pecan-BAT correlated with the corresponding nut eliciting dose (p=0.014 and p<0.001, respectively). Receiver operating curves for walnut and pecan allergy, in the prospective cohort yielded area under the curves (AUC) ranging from 0.87-0.93 for SPT and BAT. Concordant with the original study, pecan allergic patients were all co-allergic for walnut. The algorithm decreased the need for OFCs by 78.8 % with 6/240 (2.5%) falsely positives and no false negatives.