Background: Difficult intubation (DI), often unexpected, remains a primary concern for anesthesiologists. The purpose of this study was to compare the sensitivity and specificity of ULBT with sternomental, thyromental and interincisor distances in predicting difficult intubation.

Methods: In a prospective study, 380 patients undergoing general anesthesia were included. In all patients sternomental, thyromental and inter-incisor distances and the ULBT score were evaluated preoperatively. The Cormack grade was determined after the induction of anesthesia and grade 3 or 4 was considered as difficult intubation. The best points with highest accuracy were determined by ROC curve. Sensitivity and specificity of these tests in predicting difficult intubation were calculated and evaluated.

Results: In 19 (5%) patients, intubation was difficult. ULBT class III, inter-incisor distance less than 4.5 cm, thyromental distance less than 6.5 cm, sternomental distance less than 13 cm were considered as difficult intubation and there were significant differences between them and laryngeal view (P<0.05, McNemar) but there was no difference between laryngeal view in both sex. The sensitivity and specificity of ULBT is significantly higher than thyromental and sternomental and Inter-incisor distances (the specificity were respectively 91.96% vs. 64.77%, 70% and 82.27% and accuracy were respectively 91.05% vs. 76.58%, 71.32%, 81.84% and 59.53%)

Conclusion: We conclude that the specificity and accuracy of ULBT is significantly higher than inter-incisor, thyromental and sternomental distances and is more accurate in airway assessment.