A CT (computed tomography) scan or CAT (computed axial tomography) scan is an X-ray study of the body, typically the abdomen and pelvis, to evaluate a variety of complaints and disease states. Unlike traditional X-rays, a CT will provide detailed anatomic information about all of the abdominal and pelvic organs. It is a standard part of pre-treatment staging for colorectal cancer, among other diseases, and is typically combined with a PET scan. The test is frequently administered with an iodine-based, IV contrast as well as an oral contrast. Patients with a known allergy to iodine or shellfish, those with impaired kidney function or who take oral hypoglycemic, such as metformin for diabetes, must inform the doctor prior to having the test scheduled. A CT scan is frequently performed on an outpatient basis, although hospital in-patients can also have it done.