Diagnostic research mainly explores whether a certain index or technique can be used in clinic to distinguish the disease status of the diagnosed person. This kind of research can be divided into four stages, of which the main form of the first three stages is diagnostic test, by exploring the sensitivity, specificity and other parameters of a certain classification method, to evaluate the diagnostic efficacy of an index or technology; Phase 4 explores whether diagnosis can bring clinical benefits to patients. There are some key issues to consider in the design process of diagnostic studies.