Blood Tests for Cancer Screening in Average-Risk Adults
Blood tests are not recommended for cancer screening in average-risk adults with no specific medical history. The American College of Physicians explicitly recommends against serum screening tests for colorectal cancer due to lack of evidence for mortality benefit, and the U.S. Multi-Society Task Force specifically recommends against the Septin9 serum assay for screening due to insufficient evidence 1, 2.
Why Blood Tests Are Not Recommended
Blood-based tests lack the evidence base that supports mortality reduction, which is the primary outcome that matters in cancer screening 1. Currently, there are no population-based blood test screening recommendations for the majority of cancers in average-risk patients 3. The advent of liquid biopsy tests that could screen for dozens of cancers holds promise, but the cost, potential for overdiagnosis and false positives, and lack of evidence demonstrating clinical utility or improvement in health outcomes call into question their widespread use 3.
What IS Recommended for Cancer Screening
Colorectal Cancer Screening (Ages 50-75)
Begin screening at age 50 years with one of these evidence-based options 4, 2:
- Fecal immunochemical test (FIT) or high-sensitivity guaiac-based fecal occult blood test (HSgFOBT) every 2 years 4, 1, 2
- Colonoscopy every 10 years 4, 1, 2
- Flexible sigmoidoscopy every 10 years plus FIT every 2 years 4, 2
The American College of Physicians recommends colonoscopy every 10 years or annual FIT as first-tier screening options with strong evidence for mortality reduction 1. These are the only screening modalities with proven mortality benefit 1.
Age-Specific Guidance
- Ages 45-49: Consider not screening; discuss uncertainty around benefits and harms in this population 2. The American Cancer Society recommends beginning at age 45, but this is a qualified recommendation 4.
- Ages 50-75: Strong recommendation to screen—this age group has the most robust evidence for mortality benefit 4, 1, 2.
- Ages 76-85: Individualize based on prior screening history, life expectancy exceeding 10 years, and overall health status 4, 1.
- Age 85+: Discontinue screening as harms outweigh benefits 4, 1.
Other Cancer Screening Recommendations
Breast Cancer 4:
- Ages 20-39: Clinical breast examination every 3 years
- Age 40+: Annual mammography and annual clinical breast examination
Cervical Cancer 4:
- Ages 21-29: Pap test every 3 years
- Ages 30-65: Pap test plus HPV test every 5 years (preferred) or Pap test alone every 3 years
Lung Cancer 4:
- Ages 55-74 with ≥30 pack-year smoking history (current or quit within 15 years): Annual low-dose helical CT
Critical Exclusions and Pitfalls
Never use screening tests in symptomatic patients 1. Alarm symptoms including rectal bleeding, narrowed stools, unexplained weight loss, or change in bowel habits require immediate diagnostic colonoscopy regardless of any screening test results 5, 1.
Do not screen if life expectancy is less than 10 years due to comorbidities, as screening is unlikely to provide benefit 4, 1, 2.
Verify you are screening average-risk individuals only 6. Average-risk means no personal history of colorectal cancer, inflammatory bowel disease, hereditary CRC syndromes, adenomatous polyps, or family history of colorectal cancer in first-degree relatives 6, 1.
All positive stool-based tests require follow-up colonoscopy—failure to complete diagnostic workup renders the screening program ineffective 4, 1.