Background The study aim was to validate a specific nutritional risk screening tool for patients with cystic fibrosis (CF) based on clinical variables, anthropometric parameters, and dietary intake.

Methods Cross-sectional study compared present nutritional screening tool and two established nutritional assessment instruments. The kappa coefficient was used for between-group comparisons, and the sensitivity and specificity of the new instrument for diagnosis of nutritional risk were calculated.

Results 82 patients (51% female, mean age 6–18 years) were enrolled in the study. There was good agreement between the proposed screening tool and the McDonald tool (k = 0.804; 95% CI, p < 0.001) and a sensitivity and specificity of 85% and 95% respectively. Agreement with the CFF criteria was lower (k = 0.418, p < 0.001), and the sensitivity and specificity were both 72%.

Conclusion The proposed tool exhibited satisfactory agreement with the comparator instruments, and can be recommended for early identification of failure nutritional in patients with CF.