From medical student to junior doctor: how to approach the interpretation of investigations

Medical students are often taught that diagnostic tests and investigative procedures give clear information on which a diagnosis can be made or refuted. In addition, the medical literature and lay media have created the impression that with advances in technology, even the most obscure diagnosis can be made by the use of investigative tests. However, in reality, the situation is different. Most diagnoses in clinical medicine are made from the history or examination, or both, and the concomitant use of diagnostic tests and their interpretation is often suboptimal.

At the beginning of their careers in hospital based practice junior doctors often resort to a “fishing expedition” when admitting patients on the acute take, requesting multiple tests in an attempt to make a diagnosis. This can result in a cascade of unnecessary tests and inappropriate investigations, which may cause confusion and cause additional inconvenience to the patients. More specialised or invasive tests with which the junior doctor is unfamiliar may also lead to difficulties in interpretation.

To overcome these difficulties, junior doctors need to develop a logical clinical approach to the use and interpretation of diagnostic tests. This requires an understanding of:

• The main determinants of the properties of diagnostic tests

• The basic concepts of Bayesian theory

• Decision analysis

• Their integrated application to clinical medicine.12