Colorectal cancer affects less than 1% of younger adults and is still relatively rare, but the rates are rising globally. In the United States, it is the third most commonly diagnosed cancer and the second most common cancer death for both men and women. The American Cancer Society (ACS) expects colorectal cancer to cause approximately 52,580 deaths this year in 2022.
Nevertheless, while the incidence rate of colorectal cancer is on the incline, the death rate has been dropping for several decades. And it may have something to do with detecting colorectal polyps early through screenings and removing them before they can develop into cancers or finding cancers early when they are easier to treat. Furthermore, cancer screenings have made significant improvements in the treatment and prognosis of colorectal cancer over the years.
So, in this article, you will learn the different colorectal cancer screening tests that can help identify and treat colon cancer at an earlier stage. Let us weigh your options and see which test is the most appropriate for you.
A colonoscopy is a procedure that uses a flexible fiber-optic instrument, which is inserted through the rectum to examine your large intestine and the distal part of the small intestine. Your doctor usually recommends this kind of exam to look for possible causes of complaints like abdominal pain, rectal bleeding, or changes in bowel habits.
Colonoscopy is an effective screening (and treatment) tool in the prevention of colorectal cancer. Reports suggest that colonoscopy and polyp removal can reduce cancer by 76-90%. The cut-off mark for a polyp is about 1cm; less than 1cm polyps carry a risk of developing into cancer of 1%, 1cm to 2cm, the risk goes up to 10% and greater than 2cm, the risk is 40% (Ganeshan, 2013).
Regular screening should begin at age 45 to help save more lives. During this procedure, abnormal growths (polyps) are detected earlier and removed before developing into cancers.
The ACS recommends that you start getting screened for colon cancer as early as 45 years old. If your colonoscopy doesn’t find any signs of cancer, you probably won’t need another exam for ten years. However, you may need screening as often as every 1 to 5 years if you have:
- Polyps removed during a previous colonoscopy
- Prior history of colorectal cancer
- A family history of colorectal cancer
- Inflammatory bowel disease (IBD)
- Ulcerative colitis and Chron’s disease
People with Lynch syndrome usually have a colonoscopy every 1 to 3 years starting at the age of 20 to 25 years. They need thorough colonoscopy surveillance because they tend to develop colon polyps that are more difficult to detect.
Risks and complications
Colonoscopies are relatively safe and have typically few lasting effects, but sometimes they can lead to:
- Bleeding from a biopsy site
- An adverse reaction to the sedative
- A perforation (small hole) in the colon
- Abdominal pain
If you want to avoid some of the complications associated with traditional colonoscopy, you can opt for a virtual colonoscopy. It’s a procedure that uses CT scans or MRIs to take pictures of your colon. However, virtual colonoscopy is slightly less sensitive to seeing smaller polyps when compared to traditional colonoscopies. Nevertheless, despite the possible complications, the benefits of colonoscopies are usually worth the risk.
How you prepare
To have a successful colonoscopy, you must have a clear liquid diet at least 24 hours before your procedure. That means solid foods are restricted, and you’re only allowed to have clear liquids, such as:
- Pulp-free juice
- Sports drinks (gatorade)
Avoid drinking any liquids that contain red or purple dye as they can discolor your colon. Your doctor will then ask you to empty your bowel using the following methods:
- Drink a prescribed laxative
- Supplement the laxative with enemas
Be sure to follow your doctor’s instructions carefully. You may have to empty your bowel the night before the procedure, and sometimes they’ll ask you to do it again in the morning. In addition, you’ll be sedated and won’t be awake during the procedure.
Some of the possible results you can get after a colonoscopy include:
- Normal findings or negative results: This means the exam discovers no abnormalities. If you have an average colon cancer risk, your next screening will likely be in 10 years.
- Positive results: The exam finds colonic polyps, a small clump of cells forming in the colon lining. Most of them are harmless (benign), but others can develop into colon cancer over time. Doctors can remove smaller polyps during colonoscopy, but larger ones may require surgery. You may need more frequent screenings if you have a history of polyps.
- Other potential results: Colonoscopies can also detect other diseases, including diverticular disease (small pouches or sacs that form and push outward through the colon lining), hemorrhoids, inflammation, or fistulas (abnormal openings in your digestive tract).
Fecal occult blood test (FOBT)
A fecal occult blood test (FOBT) is a lab test that looks for hidden (occult) blood in your stool. Doctors will collect and analyze stool samples from your last three bowel movements. Hidden blood in the stool may indicate colon or rectal cancer or polyps in the colon or rectum. Occult blood typically passes in such small amounts that doctors can only detect it by using chemicals in FOBT.
The U.S. Preventive Services Task Force (USPSTF) recommends screening for colorectal cancer in adults using FOBT starting at age 50 years up until 75 years of age. If you have an average risk for colorectal cancer, you may take FOBT every year as early as age 45.
You may also take this test with a colonoscopy or a flexible sigmoidoscopy (a less invasive procedure that examines the rectum and sigmoid colon) every five years to check for colorectal polyps or cancer.
Risks and complications
Fecal occult blood testings are non-invasive and simple. You can do it in the comfort of your home and send it to a laboratory for analysis. However, the information an FOBT can provide can be limited and may not always be accurate. It can only detect the presence or absence of blood, but it cannot determine the cause of the bleeding.
There are no significant risks and complications in having FOBT. However, its inaccuracy can lead to potential misdiagnosis or missing out on detecting colonic polyps or cancer early when they are still treatable.
How you prepare
Various foods and medications can affect some fecal occult blood test results. For this reason, your doctor may ask you to avoid certain foods and medicines for three days before the test, including:
- Red meat
- Fruits and vegetables like broccoli and turnips
- Vitamin C supplements
- Pain relievers, such as aspirin and ibuprofen
Since this test only determines the presence or absence of blood in the stool, the result should show either of the two findings:
- Negative result. It means there’s no blood detected in your stool samples. Your doctor will likely suggest repeating the test annually. However, sometimes test results can show false-negative readings, missing the presence of blood that’s actually there. If you have a high risk of colorectal cancer, having a colonoscopy is your best option.
- Positive Result. It means the test detects blood in your stool samples. Your doctor will recommend further tests such as colonoscopy to locate the source of the bleeding. However, sometimes it could just be a false-positive, indicating that blood is present when it isn’t.
Fecal immunochemical test (FIT)
Fecal immunochemical testing (FIT) is similar to FOBT in detecting occult blood in stools. However, their difference is that FIT is newer and more accurate because foods and medicine do not interfere with the test. It also has fewer false positive results for the same reason.
Doctors also recommend taking FIT every year. It is a better alternative than fecal occult blood testing.
Risks and complications
There are no risks from using the FIT as a screening test for colonic cancers.
How you prepare
Fecal immunochemical tests are the easiest to perform among all the stool sample tests. In fact, you don’t need to do anything to prepare before the test.
The test results of the FIT are similar to the FOBT test results. They are only limited to determining the presence of blood in your stool samples. While the FIT doesn’t diagnose cancer, it can help catch colon polyps or cancer sooner when they are easier to treat.
Cologuard testing is yet another stool sample exam, except in addition to testing for blood, it looks for changes in your DNA, which can indicate colon cancer. It is basically a combination of FIT and DNA tests. You do this test by collecting the entire bowel movement and sending it to a lab, where they will check for the presence of blood and altered DNA.
Furthermore, the Centers for Disease Control and Prevention (CDC) recommends having cologuard testing once every three years. If you test positive for cologuard testing, your doctor will likely suggest following up with a colonoscopy.
CT colonography (aka, virtual colonoscopy) is an option that replaces the colonoscopy – a “let’s not and say we did” procedure. The concept of a CT scan producing an accurate, 3-dimentional image of the colon was developed in 1994 by Vining.
Similar to colonoscopy, the bowel needs to be prepped with a cathartic agent to eliminate fecal contents for the study. Carbon dioxide is used with a short tube to insufflate the intestines to properly visualize the colon. This and other minimally invasive colon cancer screening are approved by some insurances. The ideal candidate would be someone who was unable to tolerate a colonoscopy. However, similar to the other tests, if the study shows a polyp(s), the patient requires a colonoscopy.
How accurate are screening tests for colorectal cancer?
The accuracy of colonoscopy surveillance varies depending on the test. To give you an idea about your options, here is a quick summary of the accuracy rate of each colorectal screening procedure based on research:
- Colonoscopy: It remains the most accurate test and the gold standard for colon cancer detection. Research suggests that colonoscopies have an accuracy rate of up to 94%.
- Fecal occult blood tests (FOBT): A study indicates that FOBT has a relatively high sensitivity for colorectal cancer at 79%, with a corresponding pooled specificity of 94%. According to some studies, however, FOBTs diagnostic performance varies according to the anatomical site of the colorectum.
- Fecal immunochemical test (FIT): Another study concludes that the average sensitivity of FIT for colorectal cancer is 93%, and the typical specificity is around 91%. However, one study claims that symptomatic patients with both low and high risks of colorectal cancer have an overall detection rate of 100% at two hemoglobin per gram of feces, potentially reducing colonoscopy numbers to 70%.
- Cologuard testing: The accuracy of Cologuard tests in detecting colorectal cancer is believed to be 92%. However, cologuard tends to show false-positive results 14% of the time.
- Virtual Colonoscopy: Sensitivity of the virtual colonoscopy for colorectal cancer is high (96%) and is similar to a colonoscopy (95%) (Ganeshan, 2013). As a screening tool, the ability of the study to pick up polyps corresponds to the size of the polyp: the study has a sensitivity of 93% for >1cm polyps (Ganeshan, 2013).
Weigh your options
The use of screening tests can save a lot of people today, especially those with cancers. Although colorectal cancers are treatable, early detection makes a big difference in reducing the mortality rate among patients. According to the ACS, detecting colorectal cancer at its earliest stage has an 80% survival rate five years after diagnosis.
That said, you have several options for colorectal surveillance. Colonoscopy remains the best and most accurate screening test, particularly for those with symptoms and who have a high risk for colon cancer. There may be minor risks and complications, but the benefits considerably outweigh them. If you have an average risk for colorectal cancer, taking stool sample exams such as FIT and Cologuard tests every year may be enough, granted you keep getting negative results.
And while we may struggle to prevent the development of cancers, optimizing these screening tests may be the key to winning our battle with cancer.
Ganeshan D, Elsayes K, Vining D. Virtual colonoscopy: Utility, impact, and overview. World J Radiol. 2013; 5(3): 61-67