What blood tests are available for detecting colon cancer?

Blood Tests for Colorectal Cancer Detection

The primary blood test available for colorectal cancer screening is the Septin 9 blood test (Epi proColon), but it is only recommended for patients who have declined first-line screening tests like FIT or colonoscopy. 1

Available Blood Tests

FDA-Approved Blood Test

• Septin 9 (Epi proColon): The only FDA-approved blood-based test for colorectal cancer screening
  • Detects methylation of the septin 9 DNA promoter region
  • Sensitivity for colorectal cancer: 48.2-63.9%
  • Specificity: 88.4-91.5%
  • Sensitivity for advanced adenomas: only 11.2% 1
  • Not recommended as a first-line screening test by the US Preventive Services Task Force

Carcinoembryonic Antigen (CEA)

• Not recommended for screening due to:
  • Poor sensitivity (59%) and specificity (89%) for early detection 2
  • Insufficient accuracy as a single biomarker 2
  • Primarily used for monitoring recurrence after treatment, not for initial screening 3, 4
  • No evidence that CEA screening significantly affects survival or quality of life 5

Recommended Colorectal Cancer Screening Tests

Stool-Based Tests (Primarily Detect Cancer)

1. Annual Fecal Immunochemical Test (FIT)

   • Sensitivity for cancer: 73.8%
   • Specificity: 94.9%
   • Not affected by diet 6
   • Requires annual testing

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

   • Sensitivity for cancer: 37-79%
   • Specificity: 86-98%
   • Affected by diet and medications 6
   • Requires annual testing

3. Multitarget Stool DNA Test (Cologuard)

   • Sensitivity for cancer: 92.3%
   • Sensitivity for advanced precancerous lesions: 42.4%
   • Specificity: 86.6%
   • Testing interval: every 3 years 6

Structural Exams (Detect Both Cancer and Polyps)

1. Colonoscopy every 10 years
2. CT Colonography every 5 years
3. Flexible Sigmoidoscopy every 5 years
4. Double-contrast Barium Enema every 5 years 1

Important Considerations

• Follow-up protocol: Any positive stool test must be followed by colonoscopy within 3-6 months 6
• Test limitations: Stool-based tests are less likely to prevent cancer compared to invasive tests and must be repeated at regular intervals 1
• Age to begin screening: The US Preventive Services Task Force now recommends starting colorectal cancer screening at age 45 for average-risk individuals 1
• Test selection: Tests that detect both early cancer and adenomatous polyps (structural exams) should be encouraged when resources are available and patients are willing to undergo invasive testing 1

Emerging Blood-Based Biomarkers

Research is ongoing for other potential blood-based screening methods:

• Blood methylation markers
• Circulating miRNA
• Plasma protein biomarkers
• Circulating tumor DNA (ctDNA) 1

However, these are not yet approved for clinical use in colorectal cancer screening.