What is the difference between a “screening mammogram” and a “diagnostic mammogram?” In a nutshell, “screening” means you’re having a routine test, essentially a checkup. “Diagnostic” means you may have some symptoms doctors want to examine more closely using mammograms. In either case, as radiologist Dr. Bruce Hennigan explains, the availability of breast tomosynthesis or 3D mammography gives doctors more complete views of breast tissue.