Different Types of Screening Tests for Colon Cancer Signs
There are two main categories of colon cancer screening tests: visual (structural) exams and stool-based tests. Each test has its advantages, and the best option depends on personal preference, accessibility, and medical history. Here’s a breakdown of both types of screening tests:
Visual (Structural) Exams
Visual exams directly inspect the colon and rectum for polyps and cancerous growths. These exams include:
- Colonoscopy: Considered the gold standard for colon cancer screening, colonoscopy involves using a long, flexible tube (colonoscope) with a camera to examine the entire colon and rectum. If polyps are found, they can be removed during the procedure, making colonoscopy both a diagnostic and preventative tool. Colonoscopy is recommended every 10 years for average-risk individuals.
- CT Colonography (Virtual Colonoscopy): This test uses a CT scanner to produce detailed 2D and 3D images of the colon and rectum. It’s less invasive than a traditional colonoscopy and requires similar bowel preparation. CT colonography is typically done every 5 years. If polyps are detected, a follow-up colonoscopy is needed to remove them.
- Flexible Sigmoidoscopy: This test uses a shorter, flexible tube to examine only the lower third of the colon (the sigmoid colon) and the rectum. While quicker and requiring less bowel prep, it does not examine the entire colon. Flexible sigmoidoscopy is generally performed every 5 years.
Stool-Based Tests
Stool-based tests are non-invasive and can often be completed at home. They focus on detecting hidden signs of colon cancer in the stool. The options include:
- Fecal Immunochemical Test (FIT): This test detects hidden blood in the stool using antibodies that react to human hemoglobin. It’s more specific for lower GI bleeding than older tests. FIT should be done annually.
- Guaiac-Based Fecal Occult Blood Test (gFOBT): An older test, the gFOBT detects hidden blood in the stool through a chemical reaction. It is less specific than FIT and can be affected by certain foods and medications. The gFOBT is recommended annually.
- Stool DNA Test (mt-sDNA): The stool DNA test combines the FIT with a test that detects altered DNA from cancer or polyp cells shed into the stool. This test is typically done every 3 years and is offered under brand names like Cologuard.
Next Steps After a Positive Test
Any positive result from a stool-based test or a non-colonoscopy visual exam requires a follow-up diagnostic colonoscopy. This is important to confirm whether colon cancer or precancerous polyps are present. For individuals with higher risk factors (e.g., family history, certain genetic conditions), more frequent screenings may be recommended.
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