Diagnostic Accuracy of the Upper Lip Bite Test for Predicting Difficult Intubation: A Cross-Sectional Study

Background: Unexpected difficult tracheal intubation remains a major cause of anesthesia-related morbidity and mortality worldwide. Accurate preoperative airway assessment is therefore essential to reduce airway-related complications. Several bedside airway tests are available; however, none has demonstrated ideal predictive accuracy across all patient populations. The Upper Lip Bite Test (ULBT) is a simple bedside test assessing mandibular mobility and dentition, and has shown promising diagnostic performance in previous studies. Methods: This cross-sectional diagnostic accuracy study was conducted at Patel Hospital, Karachi, from July 2022 to January 2025. A total of 231 adult patients aged 20–60 years undergoing elective surgery under general anesthesia with endotracheal intubation were enrolled using non-probability consecutive sampling. ULBT was performed preoperatively and classified into three grades. Direct laryngoscopy was performed after induction of anesthesia, and laryngeal view was graded using the Cormack–Lehane (C–L) classification, which served as the reference standard. Difficult laryngoscopy was defined as C–L grade IIb–IV. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy were calculated. Results: Among 231 patients, 28 (12.1%) experienced difficult laryngoscopy. ULBT demonstrated a sensitivity of 85.7%, specificity of 98.0%, PPV of 92.3%, NPV of 96.0%, and an overall diagnostic accuracy of 95.2%. Conclusion: The Upper Lip Bite Test is a simple, rapid, and highly specific tool for predicting difficult laryngoscopy and can be effectively incorporated into routine pre-anesthetic airway assessment.