Final answer:
The coder would code 'rule out irritable bowel syndrome vs. pancreatitis' as the principal diagnosis.
Step-by-step explanation:
In this case, the coder would code the 'rule out irritable bowel syndrome vs. pancreatitis' as the principal diagnosis. The reason for this is that the phrase 'rule out' indicates that the physician is considering multiple diagnoses but has not yet determined the final diagnosis. Therefore, the coder should code the condition that is being considered but not yet confirmed as the principal diagnosis. In this case, the possibilities are irritable bowel syndrome and pancreatitis.