Education debate: clinical diagnostic reasoning.

Whilst it is clear that experienced clinicians adopt a rational approach of diagnosis, the logic of their clinical reasoning has been difficult to define. I outline here an approach based on the four categories of a complete diagnosis: Anatomical diagnosis (system involved); Pathological diagnosis (nature of the condition); Physiological diagnosis (functional consequences) and Aetiological diagnosis (background cause). Each phrase of the history and examination data is assigned to one or other of these categories as the case unfolds, with interpretations and interactions allowing sub-conclusions that gradually build to a final clinical diagnosis overall. The system has the advantage of facilitating a diagnosis individualized to the patient, rather than to some previously learned diagnostic 'checklist'. As such, it should provide an advance over current problem-based approaches to clinical diagnosis.