Improving Diagnosis in Medicine Act of 2020 This bill requires the Agency for Healthcare Research and Quality to provide grants for Research Centers of Diagnostic Excellence to support research in diagnostic quality, safety, and value and establishes the federal Interagency Council on Improving Diagnosis in Health Care within the Department of Health and Human Services. Research centers must use funds to conduct diagnostic safety and quality research, including high-impact research on novel solutions to reduce patient harm, and to support initiatives to improve diagnosis in medicine. Other activities may include developing and training the diagnostic research workforce and developing and validating measures to assess diagnostic errors.