A meta-analysis of studies, that used specific tests to predict difficult intubation in apparently normal patients, reported as follows:

• Grade 3-4 laryngoscopy occurred in 5.8 % of patients
• No test had a PPV >10 %
• Positive tests increased the likelihood of difficult intubation 3-6 fold
• Negative tests reduced the likelihood of difficult intubation 1-2 fold

The combination of Mallampati plus TMD of less than 7.0 cm increases the likelihood of difficult intubation 10 fold.