What is a diagnostic mammogram? A diagnostic mammogram is an x-ray of the breast that is used to diagnose unusual breast changes, such as a lump, pain, thickening, nipple discharge, or a change in breast size or shape. A diagnostic mammogram is also used to evaluate changes detected on a screening mammogram and requires a doctor's referral. This type of mammogram may be necessary if it is difficult to obtain a clear x-ray with a screening mammogram because of special circumstances, such as the presence of breast implants. A diagnostic mammogram takes longer than a screening mammogram because it involves more x-rays to obtain views of the breast from several angles. The technician may magnify a suspicious area to produce a detailed picture that can help the doctor make an accurate diagnosis.