Colorectal Cancer Screening Options

Last year, a new blood test for colorectal cancer screening was approved by the Food and Drug Administration (FDA).

Called Shield™, the test checks for DNA changes that signify the presence of tumors. It is the first blood test approved for primary screening in adults ages 45 and older who are at average risk for colorectal cancer. Before the launch of Shield, only one other blood test (Epi proColon®) was approved in 2016. However, it was only for use in those aged 50 years or older.

These blood-based screening tests join a number of stool tests offered as alternatives to colonoscopy in average-risk patients (without personal or family history of colon cancer, personal history of colon polyps, or personal history of inflammatory bowel disease). This includes the latest update to the Cologuard® multitarget stool DNA test called Cologuard Plus™. It was also approved by the FDA in 2024.

Despite the new advances in blood and stool testing, colonoscopy remains the gold standard for colon cancer detection. With colonoscopy, physicians highly trained in cancer detection examine the entire colon for abnormal growths. Stool and blood tests rely on detecting blood proteins or DNA biomarkers. These tests are less accurate in detecting colorectal cancer than direct visualization tests like colonoscopy, virtual colonoscopy and sigmoidoscopy.

The sensitivity rate in detecting colon cancer with blood and stool tests varies between the different testing methods, meaning a potentially more significant chance of inaccurate results depending on the test administered. There is also the potential for false negatives when detecting precancerous polyps called advanced adenomas. Accuracy in detecting these types of growths can be as low as 13%.

It’s not to say that stool-related and blood-based tests are a waste of time. Alternative testing is still far better than no testing at all. Patients need to be aware of the limitations of these tests, especially the higher chance of false negatives and the low ability to detect advanced adenomatous polyps.

They also must be performed more frequently than colonoscopies.

Stool Tests

• Guaiac-Based Fecal Occult Blood Test (gFOBT): Detects blood in the stool from polyps or cancers. Recommended once per year.

• Fecal Immunochemical Test (FIT): Uses antibodies to identify blood in the stool. Recommended once per year.

• FIT-DNA Test: Identifies blood and biomarkers associated with colorectal cancer and precancerous growths. Recommended once every three years.

• Blood Tests: Check for DNA markers associated with colorectal cancer. This test needs to be repeated every one to three years.

• Flexible Sigmoidoscopy: A minimally invasive procedure using a thin tube to check the lower part of the colon. This test should be done every five years or every 10 years with a yearly FIT test.

• Colonoscopy: Similar to a sigmoidoscopy, this test allows your doctor to check the lining of your entire colon using a thin, flexible tube. The recommended screening interval is every 10 years for average-risk patients without findings of precancerous polyps on the initial screening.

• CT Colonography: This is a virtual colonoscopy using computer and X-ray technology to provide imaging of the colon. This should be undertaken every five years. It is only available where radiologists are trained to interpret the test.

GastroIntestinal Specialists recommend colonoscopy wherever possible, starting at age 45 for all patients of average risk and potentially earlier if at higher risk. It is the most comprehensive screening, catching 95% of colorectal cancer. If precancerous polyps are discovered, they can be removed during the procedure to prevent cancer. Not only is this a screening test, but it also functions as a preventive procedure against cancer. Our gastroenterologists can explain the range of alternatives for patients who prefer a noninvasive option. They will help develop the best screening plan based on your individual risk and personal preference.

Dr. Nicolas T. LaBarre is a board-certified gastroenterologist at GastroIntestinal Specialists, the largest independent gastroenterology group in Northwest Louisiana. Call (318) 631-9121 to schedule an appointment or visit gis.md.