Colorectal Cancer Screening Tests: Purpose, Test Details & Results

Colorectal cancer (CRC) is one of the most common and deadly cancers worldwide, but early detection through effective screening can dramatically reduce both incidence and mortality. Whether you’re a patient, a caregiver, or a healthcare provider, understanding the purpose, details, and outcomes of CRC screening tests is essential for making informed decisions about prevention and care. This article provides a comprehensive, evidence-based overview of why screening matters, what the main tests are, and how to interpret results and follow-ups—using the latest research and expert recommendations.

Purpose of Colorectal Cancer Screening Tests

Colorectal cancer often develops silently, with no symptoms until it reaches an advanced stage. The primary goal of screening is to detect cancer early, when it’s most treatable, or even to prevent it by finding and removing precancerous polyps. Screening can save lives, reduce treatment complexity, and improve quality of life for millions of people.

Objective	Benefit	Challenge	Source(s)
Early Detection	Reduces mortality	Participation/adherence	1 2 4 5
Prevention	Removes polyps	Overdiagnosis/false results	1 2 7
Population Health	Reduces incidence	Resource limitations	4 5

Table 1: Key Purposes and Challenges of Colorectal Cancer Screening

Why Screening Matters

Colorectal cancer ranks among the top causes of cancer death globally, but it’s also one of the most preventable and treatable cancers—if found early. Screening tests are designed to identify cancer or precancerous growths (adenomas) before symptoms appear. Multiple large studies and systematic reviews have shown that organized screening programs lower both incidence and mortality of CRC, especially in high-risk and average-risk populations 1 2 5.

Preventing Cancer, Not Just Finding It

Unlike many cancers, CRC screening doesn’t just detect disease—it also prevents it. Many CRCs begin as benign polyps that can be removed during colonoscopy or identified through stool-based testing, preventing progression to cancer 1 2 7. This proactive approach is unique and makes regular screening especially valuable.

Who Should Be Screened?

• Average-risk adults: Most guidelines recommend starting regular screening at age 45–50, continuing through age 75; some groups (like African Americans) may benefit from starting earlier 3 7.
• High-risk individuals: Those with a family history or certain genetic syndromes may need earlier or more frequent screening.
• Elderly & comorbid patients: Screening decisions should be individualized based on health status and life expectancy 3 7.

Barriers and Risks

Despite the benefits, many people remain unscreened due to lack of awareness, access, or reluctance to undergo testing. Screening also carries risks, such as false positives, overdiagnosis, and—rarely—procedural complications like bleeding or perforation 1 2 4 5. Balancing these benefits and risks is crucial for patients and healthcare systems.

Colorectal Cancer Screening Tests Details

There is no single “best” test for everyone—each CRC screening method has unique advantages, disadvantages, and practical considerations. The choice depends on patient preference, risk factors, access, and health system resources.

Test Type	Frequency	Pros/Cons	Source(s)
Colonoscopy	Every 10 years	Gold standard; invasive; high sensitivity	3 5 7
FIT	Annually	Noninvasive; practical; high specificity	3 5 6 7
gFOBT	Annually	Widely available; lower sensitivity	1 2 5 7
Stool DNA-FIT	Every 3 years	High sensitivity; more false positives	3 6 7
CT Colonography	Every 5 years	Visualizes colon; radiation exposure	2 3 7
Sigmoidoscopy	Every 5 yrs	Direct view (partial colon); less invasive	2 3 7
Blood Test	Varies	Noninvasive; lower sensitivity	4

Table 2: Overview of Colorectal Cancer Screening Test Options

Colonoscopy

Colonoscopy is considered the gold standard for CRC screening. It involves visual inspection of the entire colon and rectum using a flexible camera. Polyps can be removed during the procedure, offering both diagnostic and preventive benefits 3 5 7. Colonoscopy is recommended every 10 years for average-risk adults.

Pros:

• Detects and removes polyps in a single session
• Highest sensitivity for cancer and advanced adenomas

Cons:

• Invasive (requires bowel prep and sedation)
• Rare but serious complications: bleeding (~1 in 1,000), perforation (~1 in 3,000) 2
• May be less accessible in some regions

Fecal Immunochemical Test (FIT)

FIT detects blood in stool using antibodies specific to human hemoglobin. It’s noninvasive, requires no dietary restrictions, and can be done at home. FIT is typically performed annually and has a high specificity (94%) and moderate sensitivity (0.74) for cancer 2 3 5 6 7.

Pros:

• High specificity
• Easy, at-home collection
• No dietary/medication restrictions

Cons:

• Needs annual repetition
• Positive results require follow-up colonoscopy

Guaiac Fecal Occult Blood Test (gFOBT)

gFOBT uses a chemical reaction to detect hemoglobin in stool. It has lower sensitivity than FIT and requires dietary restrictions to reduce false positives 1 2 5 7.

Pros:

• Inexpensive, widely available

Cons:

• Lower sensitivity (0.50–0.75) 2
• Requires multiple samples and dietary restrictions

Stool DNA-FIT (Multitarget Stool DNA Test)

This test combines FIT with molecular assays detecting abnormal DNA in stool. It’s repeated every 3 years and offers very high sensitivity (0.92) for cancer—outperforming FIT, but with slightly lower specificity (0.86) 6.

Pros:

• Highest sensitivity among stool tests
• Detects both blood and DNA changes

Cons:

• More false positives than FIT
• More expensive

CT Colonography (Virtual Colonoscopy)

This imaging test uses low-dose CT scans to visualize the colon every 5 years. It’s less invasive than colonoscopy but still requires bowel prep and exposes patients to radiation 2 3 7.

Pros:

• Noninvasive visualization of colon

Cons:

• Cannot remove polyps; positive findings need colonoscopy
• Radiation exposure
• May detect unrelated abnormalities (extracolonic findings)

Flexible Sigmoidoscopy

Sigmoidoscopy inspects the lower (distal) colon and rectum, usually every 5 years. It’s less invasive than colonoscopy but may miss cancers in the upper colon 2 3 7.

Pros:

• Less invasive, no sedation needed

Cons:

• Only examines part of the colon
• Still requires bowel prep

Blood-Based Tests

Recently, blood-based tests (e.g., Epi proColon®) have become FDA-approved for CRC screening. While convenient and noninvasive, their sensitivity for early-stage cancer is lower than stool-based or visual tests 4.

Pros:

• Easiest to complete (simple blood draw)
• May improve screening participation

Cons:

• Lower sensitivity—may miss early cancers

Choosing the Right Test

The best test is the one that gets done. Guidelines universally recommend offering multiple options, allowing patients and providers to choose based on preferences, risk, and availability 3 7. Colonoscopy and FIT are generally considered first-line choices for most average-risk adults, with other tests as acceptable alternatives.

Colorectal Cancer Screening Tests Results & Follow-Up

Interpreting CRC screening results and ensuring appropriate follow-up is as important as the screening itself. A positive test doesn’t mean cancer is present—it means further diagnostic steps are required.

Result Type	Next Step	Impact/Consideration	Source(s)
Negative	Continue regular screening	Does not rule out future risk	1 2 7
Positive	Colonoscopy for confirmation	May be false positive	2 5 6 9
Inconclusive	Repeat or alternative testing	Delays diagnosis	9
Detected Lesion	Removal/biopsy; surveillance	Early treatment/prevention	2 6 8

Table 3: Interpreting Screening Results and Required Actions

Understanding Test Outcomes

• Negative Result: Most people will have negative results. This means no blood, suspicious DNA, or visible polyps/cancers were found. Regular screening should continue at recommended intervals 1 2 7.
• Positive Result: A positive result on any non-colonoscopy test (FIT, gFOBT, stool DNA) requires a diagnostic colonoscopy for confirmation and possible polyp removal 2 5 6 9.
• Inconclusive/Invalid: Sometimes, a test may not yield a clear result due to improper sample collection or processing. Retesting or using an alternative method may be necessary 9.

Importance of Follow-Up

A critical but often overlooked step is ensuring timely follow-up after an abnormal screening test. Data show that up to 41% of patients with a positive stool test may not complete the necessary follow-up colonoscopy, delaying diagnosis and reducing the benefit of screening 9. Health systems and providers must prioritize follow-up to maximize outcomes.

What Happens After Colonoscopy?

• No Findings: If the colonoscopy is clear, the next screening is typically due in 10 years (for average-risk adults).
• Polyp(s) Found: Polyps are usually removed during the procedure. The type, size, and number of polyps determine future surveillance intervals—ranging from 3 to 5 years for higher-risk findings 3 7.
• Cancer Detected: Early-stage cancers detected via screening are more likely to be curable with less invasive treatment 1 8.

Risks and Limitations

While screening saves lives, it’s not perfect:

• False Positives: Can lead to unnecessary procedures and anxiety 1 2 6.
• False Negatives: Rare, but possible—no test is 100% accurate 1 2.
• Complications: Colonoscopy can cause bleeding or perforation, though these are rare events 2.

Equity and Access in Screening and Follow-Up

Disparities remain in CRC screening rates and follow-up, especially among minority, lower-income, and less-engaged patients 9. Efforts to improve education, reduce barriers, and provide options like blood-based or stool-based tests can enhance participation and outcomes.

Conclusion

Colorectal cancer screening is one of the most effective tools in the fight against cancer. Understanding the purpose, available tests, and how to interpret and act on results is essential for patients and providers. Here’s what to remember:

• Early detection saves lives: Screening reduces both incidence and mortality from colorectal cancer 1 2 3 7.
• Multiple screening options: Colonoscopy and FIT are first-line tests, but stool DNA, sigmoidoscopy, CT colonography, and blood tests are viable alternatives 3 5 6 7.
• Follow-up is critical: Positive tests require timely colonoscopy, and proper follow-up ensures the full benefit of screening 2 6 9.
• Individualized approach: The best test is the one the patient is willing and able to complete; personal risk factors, preferences, and resource availability should guide choices 3 7.
• Continuous improvement: Addressing barriers in participation and follow-up, and expanding access to less invasive tests, are key to reducing the global burden of colorectal cancer 4 5 9.

Stay informed, talk to your healthcare provider, and don’t delay your screening—early action can make all the difference.