Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom we would use it in practice)?
The study should include both patients with common presentations of the target disorder and those with conditions that are commonly confused with the target disorder of interest. If the study only includes patients with severe symptoms of the target disorder (and who would be very obvious to diagnose) it is not likely to be useful to us. We need to find out if patients with varying severity of the disease were included in the study and also whether it includes patients with target disorders that are often confused with this one. For example, anaemic patients can be symptomatic or asymptomatic and the anaemia can result from a number of causes - we would want to ensure that the study we retrieved included patients with a variety of presentations and symptoms.
Reviewing the ferritin study, it included consecutive patients over the age of 65 who were admitted with anaemia to a university-affiliated hospital in Canada. It excluded patients from institutions and patients who were too ill or who had severe dementia. No details are provided on the definitions used for 'too ill' or 'severe dementia'.
- Was there an independent, blind comparison with a reference ("gold") standard of diagnosis?
- Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom we would use it in practice)?
- Was the reference standard applied regardless of the diagnostic test result?
- Was the test (or cluster of tests) validated in a second, independent group of patients?