I would be very interested to know if anyone has experience of planning or conducting a diagnostic trial. I am planning a clinical trial of a new TB diagnostic in South Africa. The majority of diagnostic evaluation focuses on performance or accuracy of the diagnostic test (i.e.sensitivity, specificity, PPV, NPV). We want to go beyond this and look at the impact on clinical outcomes. There is not a huge body of literature on diagnostic trials with patient-important outcomes and there are many things which make them very different from drug trials or vaccine trials. One area where there have been RCTs is malaria rapid diagnostic tests - here several trials have shown that although the tests performed well they did not necessarily lead to the 'correct' clinical decision or prescription of antimalarials. Hence they would not have the impact expected from the initial diagnostic accuracy data.
One particular aspect that we are wrangling with is the ethics of randomisation so we are also considering a quasi-experimental design for the study. Again I would be very interested to hear from anyone who has experience of quasi-experimental studies.
Good point. There isn't alot of work being done on diagnostic studies, particularly in the area of NTD's which i work in. We have recently started to look at 2 diagnostic methods for detecting VL (Kala-azar) in East Africa but this will primarily be looking at specificity and sensitivity against what has been the standard test (spleen/bone marrow aspirates) which is invasive and cannot be done outside the hospital set up. The results would probably help in improving the management of the condition even though its not a clinical trial in the strictest sense of the definition.
This would probably form the basis of looking at diagnostics in detail beyond specificity and sensitivity depending on the outcome.