What blood tests are available for colon cancer screening?

Blood Tests for Colorectal Cancer Screening

There are currently no recommended standalone blood tests for colorectal cancer screening, as stool-based tests (FIT, gFOBT, and sDNA-FIT) and direct visualization methods (colonoscopy, flexible sigmoidoscopy, and CT colonography) remain the established screening options recommended by major guidelines. 1, 2

Current Recommended Screening Options

Stool-Based Tests

1. Fecal Immunochemical Test (FIT)

   • Uses antibodies to detect human blood in stool
   • Higher sensitivity (73.3%) than traditional guaiac-based tests (33.3%) with similar specificity (>95%) 2
   • Requires only 1-2 samples with no dietary restrictions
   • Recommended annually 1
   • Higher participation rates than gFOBT 3

2. Guaiac-based Fecal Occult Blood Test (gFOBT)

   • Detects pseudoperoxidase activity of heme in human blood
   • Proven to reduce colorectal cancer mortality by 15-33% in randomized trials 1
   • Requires dietary restrictions during testing
   • Recommended annually 1
   • Lower sensitivity compared to newer tests 4

3. Multitarget Stool DNA-FIT (sDNA-FIT)

   • Combines FIT with detection of DNA biomarkers for cancer
   • Higher sensitivity than FIT alone for cancer (92.3% vs 73.8%) and advanced adenomas (42.4% vs 23.8%) 2
   • Better at detecting sessile serrated polyps (42% vs 5%)
   • Lower specificity than FIT alone (86.6% vs 94.9%)
   • Recommended every 1-3 years 1

Direct Visualization Tests

1. Colonoscopy

   • Most sensitive test for detecting both cancer and precancerous polyps
   • Allows for removal of polyps during procedure
   • Recommended every 10 years for average-risk individuals 1, 2
   • Only recommended method for high-risk patients

2. Flexible Sigmoidoscopy

   • Examines only the lower third to half of the colon
   • Recommended every 5 years, or every 10 years with annual FIT 1

3. CT Colonography

   • Uses X-ray imaging to visualize the colon
   • Recommended every 5 years 1

Blood Tests in Development

While no blood tests are currently recommended in major screening guidelines, research is ongoing in this area. The USPSTF specifically notes that "because other effective tests are available" (referring to the recommended screening strategies above), serum tests are not included in current recommendations 1.

Important Considerations for Screening

• Age for Screening: Guidelines recommend starting at age 45 for average-risk adults 2
• Risk Stratification: Screening recommendations differ based on risk factors:
  • Average risk: Multiple options available
  • High risk (family history, genetic syndromes, inflammatory bowel disease): Colonoscopy is preferred 1
• Follow-up: Any positive stool-based test must be followed up with colonoscopy 2
• Test Performance: Sensitivity varies by test type and location of lesions
  • FIT has lower sensitivity for proximal colon lesions compared to distal colon (16.3% vs 30.7%) 5
  • One-time FIT has 65.8% sensitivity for invasive cancer but only 27.1% for advanced neoplasia 5

Clinical Implications

• The absence of recommended blood tests for colorectal cancer screening means clinicians should focus on established screening methods
• Patient adherence significantly impacts screening effectiveness, so discussing available options and their pros/cons is essential
• For patients reluctant to undergo colonoscopy or stool testing, emphasize that no validated blood test alternative currently exists
• Regular screening with established methods remains the most effective approach to reducing colorectal cancer mortality

Blood tests for colorectal cancer screening remain an area of active research but have not yet demonstrated sufficient sensitivity and specificity to be included in major screening guidelines.