[Practical exercises on diagnostic test interpretation]

Although medical literature places great emphasis on therapy, diagnosis remains an essential part of medical practice. We present four clinical cases that show the interaction between pre-test probabilities and the accuracy of investigations (sensitivity, specificity, predictive values and likelihood ratios) The first example studies the influence of meningeal signs in the diagnosis of meningitis. The second one analyzes the diagnostic utility of investigations in patients suspected of dementia. The third example examines the change in the probability of carpal tunnel syndrome depending on the physical examination and the electrodiagnostic studies. The last example explains the use of ROC curves in the diagnosis of demyelinating disease with CSF-IgG index.