Colonoscopy is considered the gold standard for colon cancer and cancer screening. However, other types of tests may be appropriate for you. These tests usually require colonoscopy as a follow-up when abnormalities are revealed. They include: Sewage testing (annually). There are different types of tests using the sewage sample you provide for analysis. A guaiac-based fecal occult test (gFOBT) and fecal immunochemical test (or FIT test) look for blood on the stool, while a FIT-DNA test looks for altered DNA, which may be a sign of cancer. Sigmoidoscopy (every 10 years). This is a slightly invasive test similar to colonoscopy, but only enters the last third of your descending colon or sigmoid colon. Virtual colonoscopy / CT colonography. These non-invasive experiments use X-ray images and computers to produce colonial images without physical contact.