Your first stop should be the online Pubmed training material from from the NCBI. Make sure you check below for Quick Tours, a series of concise videos explaining a number of PubMed's advanced features. If you have the time, you can work through the NCBI's self-directed tutorial.
If you have specific study designs in mind, you can run and filter your search with the NCBI's Clinical Queries.
Looking for tests of diagnostic accuracy? GetTheDiagnosis.org may already have found what you need. This tool is a collaborative database that includes the sensitivity and specificity of history questions, physical exam findings, and lab and imaging tests.