The use of information theory in evaluating the contribution of radiological and laboratory investigations to diagnosis and management

Using information theory, the value of radiological and laboratory investigations has been assessed in the diagnosis and management of 67 patients suspected of having inflammatory polyarthritis. There were only three changes in diagnosis made as a result of the investigations. Both the radiological and laboratory tests supplied a small but significant amount of information in improving the physician's confidence in diagnosis. Changes in management occurred more frequently but the final management decision differed from the pre-investigation decision in only 17 of the 67 patients (25%). Radiological examination failed to decrease uncertainty using a simple ‘change in uncertainty’ measure. Both types of investigation supplied a limited but significant amount of information towards the final management decision, although the contribution from radiology was only significant when viewed before the receipt of the results of the laboratory tests. In view of the limited value of the investigations — particularly radiology — in this study, it is important to fully assess present and future diagnostic procedures especially in relation to patient management.