What are the indications for a colonoscopy (colon examination) in adults with varying risk factors and medical histories, including family history of colorectal cancer, gastrointestinal symptoms, and age?

Indications for Colonoscopy in Adults

Colonoscopy is indicated for average-risk adults beginning at age 45 years, with earlier and more frequent screening (starting at age 40 or 10 years before the youngest affected relative's diagnosis) for those with a first-degree relative diagnosed with colorectal cancer before age 60 or two or more first-degree relatives diagnosed at any age. 1

Average-Risk Screening Indications

For asymptomatic adults at average risk, colonoscopy should begin at age 45 years and be repeated every 10 years if normal. 1

• The American College of Gastroenterology gives a strong recommendation for screening adults between ages 50-75 years, with colonoscopy every 10 years as a primary screening modality. 1
• Screening between ages 45-49 years carries a conditional recommendation, reflecting the rising incidence of early-onset colorectal cancer. 1
• The US Preventive Services Task Force assigns Grade A evidence for screening ages 50-75 years and Grade B for ages 45-49 years. 1
• Screening should continue through age 75 years, with selective screening for ages 76-85 based on prior screening history and life expectancy greater than 10 years. 1

High-Risk Indications Based on Family History

First-Degree Relative with CRC Diagnosed Before Age 60

Colonoscopy should begin at age 40 years OR 10 years before the age at diagnosis of the affected relative (whichever comes first), and be repeated every 5 years. 1, 2

• This represents a strong recommendation across all major gastroenterology societies. 1
• The 5-year interval (not 10-year) is critical for this high-risk group. 1, 2

Two or More First-Degree Relatives with CRC at Any Age

Colonoscopy should begin at age 40 years OR 10 years before the youngest affected relative's diagnosis (whichever is earlier), repeated every 5 years. 1, 2

• This applies regardless of the age at which relatives were diagnosed. 1
• These individuals have a 3-4 times higher lifetime risk compared to average-risk populations. 2

Single First-Degree Relative with CRC Diagnosed at Age ≥60

Colonoscopy should begin at age 40 years and be repeated every 10 years (following average-risk intervals but starting earlier). 1, 2

• Annual FIT is an acceptable alternative if colonoscopy is declined. 1, 2
• This represents only modestly elevated risk, approximately 1.9-2 fold increased. 2

First-Degree Relative with Advanced Adenoma

If the advanced adenoma was diagnosed before age 60, colonoscopy should begin at age 40 years or at the age of onset in the relative (whichever is first), repeated every 5-10 years. 1, 2

• Advanced adenoma is defined as ≥1 cm, villous features, or high-grade dysplasia. 2
• Documentation of the advanced nature of the adenoma is critical for determining screening intensity. 2

Second- or Third-Degree Relatives with CRC

Colonoscopy should begin at age 45 years and be repeated every 10 years. 1, 2

• This follows average-risk screening protocols with standard age initiation. 1

Diagnostic Indications (Not Screening)

Any gastrointestinal symptoms warrant immediate diagnostic colonoscopy regardless of age, not screening protocols. 3

• Hematochezia, melena, or iron deficiency anemia require diagnostic evaluation. 3
• Unexplained weight loss, change in bowel habits, or abdominal pain necessitate diagnostic workup. 3
• These presentations should never be managed with stool-based screening tests. 3

Post-Polypectomy Surveillance Indications

After removal of 2 non-cancerous polyps, surveillance colonoscopy is indicated in 3 years initially, with potential extension to 5 years if subsequent surveillance shows no polyps or only 1-2 small tubular adenomas with low-grade dysplasia. 2

• If polyps were small (<1 cm) tubular adenomas with low-grade dysplasia, the next colonoscopy is in 5-10 years. 2
• If any polyp was ≥1 cm, had villous features, high-grade dysplasia, OR there were 3-10 total adenomas, surveillance is in 3 years. 2
• If piecemeal removal was performed, 2-6 month follow-up is necessary to verify complete removal. 2

Inflammatory Bowel Disease Indications

In patients with ulcerative colitis or Crohn disease with colonic involvement, surveillance colonoscopy should begin 8-10 years after symptom onset and be repeated every 1-3 years. 4

• The interval depends on disease extent, duration, and presence of other risk factors like primary sclerosing cholangitis. 4

Hereditary Syndrome Indications

Lynch Syndrome (Hereditary Nonpolyposis Colorectal Cancer)

Colonoscopy should begin at age 25 years (or 10 years before the youngest affected relative's diagnosis) and be repeated every 1-2 years. 2, 4

• Genetic counseling and testing should be offered when multiple relatives have polyps or cancer, especially before age 50. 2

Familial Adenomatous Polyposis

Annual flexible sigmoidoscopy should begin at puberty (around age 10-12 years). 2, 4

• Once polyposis is confirmed, colonoscopy is typically required every 1-2 years. 4

Peutz-Jeghers Syndrome

Screening colonoscopy should begin at age 8 years, repeated at age 18 years if normal, then every 3 years thereafter. 4

Sessile Serrated Adenomatous Polyposis

Annual colonoscopy should begin as soon as the diagnosis is established. 4

Critical Caveats and Common Pitfalls

• Family history information is often incomplete or inaccurate—verify the exact diagnosis, age at diagnosis, and relationship of affected relatives whenever possible. 1, 2
• Do not wait until age 45 or 50 to begin screening if any first-degree relative has CRC—screening must start at age 40 at the latest. 2
• Do not use 10-year intervals if a first-degree relative was diagnosed before age 60 or if there are two or more affected first-degree relatives—these situations require 5-year intervals. 2
• Single-panel guaiac fecal occult blood test performed in the office during digital rectal examination is NOT an acceptable screening method due to very low sensitivity. 1
• Quality indicators matter: colonoscopy should achieve ≥25% adenoma detection rate in men, cecal intubation, and ≥6 minute withdrawal time. 3