Diagnostic informatics encompasses the role of information technology in key areas of the diagnostic testing (pathology and medical imaging) process, including the selection of appropriate tests and interpretation and follow-up of test results. We present three case studies employing diagnostic informatics methodologies to demonstrate their potential use and value in health services research: (1) Data analytics applied to diagnostic data linked with patient outcome data as a means of enhanancing the monitoring of the quality and appropriateness of diagnostic test choices; (2) Business process modelling which can help to highlight healthcare processes in the diagnostic pathway as a means of improving safety and performance, and (3) Consumer involvement in the diagnostic research process to assist in the establishment of person-centred test result management systems. The case studies provide evidence of the role that diagnostic informatics can have in improving the quality and safety of patient care.