Colonoscopy Screening: When to Start and How Often

Colorectal cancer is the third most common cancer diagnosed in both men and women in the United States, and it is the second leading cause of cancer death. Yet it is also one of the most preventable cancers because screening can detect and remove precancerous polyps before they become malignant. The challenge is that screening guidelines have evolved significantly in recent years, leaving many people unsure about when to start and how often to be tested.

The Shift to Age 45

For decades, the standard recommendation was to begin colorectal cancer screening at age 50 for average-risk adults. That changed in 2018 when the American Cancer Society lowered its recommended starting age to 45, citing a troubling rise in colorectal cancer diagnoses among younger adults.

Between 1995 and 2019, colorectal cancer incidence increased by 51% among adults under 50. The reasons for this trend are not fully understood, though researchers have pointed to rising obesity rates, dietary changes, and alterations in the gut microbiome as possible contributing factors.

In 2021, the U.S. Preventive Services Task Force followed suit, updating its recommendation to begin screening at age 45 for all adults at average risk. The American College of Gastroenterology (ACG) also recommends starting at 45.

Screening Options

Colonoscopy is the most commonly discussed screening method, but it is not the only option. Current guidelines recognize several approaches:

Colonoscopy

A direct visual examination of the entire colon using a flexible scope. If polyps are found, they can be removed during the same procedure. For average-risk adults with a normal result, the recommended screening interval is every 10 years. Colonoscopy requires bowel preparation and sedation, which are the primary barriers to participation.

Stool-Based Tests

These are non-invasive alternatives that can be done at home:

• Fecal immunochemical test (FIT): Detects hidden blood in the stool. Done annually. Sensitivity for colorectal cancer is approximately 74%.
• Stool DNA test (Cologuard): Tests for both blood and DNA markers associated with cancer and advanced polyps. Done every three years. Sensitivity for colorectal cancer is approximately 92%, but it has a higher false-positive rate than FIT.
• Guaiac-based fecal occult blood test (gFOBT): An older method largely replaced by FIT, done annually.

A positive stool-based test requires follow-up with a colonoscopy. These tests are most effective when done consistently at the recommended intervals.

Other Options

• CT colonography (virtual colonoscopy): A CT scan of the colon, done every five years. Requires bowel prep but not sedation. If abnormalities are found, a standard colonoscopy is needed.
• Flexible sigmoidoscopy: Examines only the lower third of the colon, done every five years (or every 10 years if combined with annual FIT). Less commonly used in the United States today.

When to Screen Earlier

Some individuals should begin screening before age 45 due to elevated risk. These include people with:

• A first-degree relative (parent, sibling, or child) diagnosed with colorectal cancer or advanced adenoma, especially if diagnosed before age 60. The ACG recommends starting screening 10 years before the youngest affected relative's age at diagnosis, or at age 40, whichever is earlier.
• Inflammatory bowel disease (Crohn's disease or ulcerative colitis), particularly if it involves the colon and has been present for eight or more years.
• Known genetic syndromes such as Lynch syndrome (hereditary nonpolyposis colorectal cancer) or familial adenomatous polyposis (FAP). Screening for these conditions often begins in the teens or early twenties.
• A personal history of colorectal cancer or adenomatous polyps.
• A history of abdominal or pelvic radiation for a prior cancer.

When to Stop Screening

The USPSTF recommends screening through age 75 for all adults. Between ages 76 and 85, the decision to continue screening should be individualized based on overall health, life expectancy, and prior screening history. Screening is generally not recommended after age 85, as the risks of the procedure begin to outweigh the potential benefits for most individuals.

A person who has been consistently screened with normal results and has no additional risk factors may reasonably stop screening at 75. A person who has never been screened may benefit from an initial screening even in their late 70s.

The Best Test Is the One You Complete

Gastroenterologists often say that the best screening test is the one a patient will actually do. If the prospect of bowel preparation and sedation is keeping you from getting screened, a stool-based test is a valid alternative. A FIT test done consistently every year catches the majority of colorectal cancers. The most dangerous choice is not getting screened at all.

Approximately 30% of adults aged 50 to 75 in the United States are not up to date on colorectal cancer screening. Closing this gap would prevent an estimated 19,000 colorectal cancer deaths per year.