From the Guidelines
To rule out colorectal cancer, a total colonoscopy is the recommended diagnostic test, as it allows for direct visualization of the entire colon and rectum, and enables biopsy of suspicious lesions 1. This procedure should be performed by a gastroenterologist or colorectal surgeon and typically requires bowel preparation with solutions like GoLYTELY or MoviPrep the day before. Some key points to consider when ordering diagnostics for colorectal cancer include:
- A flexible sigmoidoscopy may be used to examine the rectum and lower colon but doesn't visualize the entire colon 1.
- Stool-based tests, such as the fecal immunochemical test (FIT) and the guaiac-based fecal occult blood test (gFOBT), can detect hidden blood in stool, and stool DNA tests like Cologuard can detect altered DNA from cancer cells 1.
- Imaging studies, such as CT colonography (virtual colonoscopy), can provide detailed images of the colon without requiring scope insertion, though any abnormalities would still require follow-up colonoscopy 1.
- Blood tests, like complete blood count, may detect anemia from chronic bleeding, and carcinoembryonic antigen (CEA) can be elevated in some cancer cases, though it's not specific enough for screening 1. The selection of these tests should be based on patient risk factors, symptoms, and previous screening history, with colonoscopy remaining the most definitive diagnostic tool 1. It's also important to consider the recommendations from the US Preventive Services Task Force, which suggests that direct visualization tests, such as colonoscopy, CT colonography, and flexible sigmoidoscopy, can be used to screen for colorectal cancer 1. Additionally, the American College of Physicians recommends screening for colorectal cancer in average-risk adults between the ages of 50 and 75 years, and suggests selecting the screening test based on a discussion of benefits, harms, costs, and patient preferences 1.
From the Research
Diagnostics for Ruling Out Colorectal Cancer
To rule out colorectal cancer, several diagnostics can be ordered, including:
- Colonoscopy: considered the gold standard for colorectal cancer screening, as it allows for direct visualization of the entire colon and removal of precancerous adenomatous lesions 2, 3, 4
- Fecal occult blood test (FOBT): a non-invasive test that detects blood in the stool, which can be a sign of colorectal cancer 5, 6
- Other screening tests: such as computed tomographic (CT) colonography, magnetic resonance (MR) colonography, and wireless capsule endoscopy (PillCam Colon) 5
Sensitivity and Specificity of Diagnostics
The sensitivity and specificity of these diagnostics vary:
- Colonoscopy: has a high sensitivity and specificity for detecting colorectal cancer and precancerous lesions 2, 3
- FOBT: has a lower sensitivity and specificity for detecting colorectal cancer, especially for small adenomatous polyps 5, 6
Recommendations for Screening
The American Cancer Society and other major health organizations recommend screening for colorectal cancer starting at age 50 for average-risk individuals 3, 4