The diagnostic pursuit of gastrointestinal symptoms.

The present article attempts to model the reasoning underlying the process of diagnostic workup in a patient with GI symptoms. Diagnostic reasoning consists of two consecutive and repetitive steps. Test procedures help to contract a list of multiple competing diagnoses to one focal diagnosis. In a subsequent step, the focal diagnosis again becomes expanded to a second list of new diagnoses that are more precise than those on the first list. In the process of expansion, the focal diagnosis itself serves as a test with its own sensitivity values to generate the second list of associated diagnoses. The process of contraction and expansion repeats itself, until the focal diagnosis of the last contraction is no longer expansible or until diagnostic knowledge gained from further expansion loses therapeutic relevance. The process of contraction and expansion can be formalized by Bayes' formula.