Colorectal cancer screening
Colorectal cancer screening involves various tests aimed at detecting abnormalities in the large intestine and rectum, crucial for early diagnosis and effective treatment of colorectal cancer. These screenings are particularly important because early-stage colorectal cancers often do not present symptoms, making routine testing vital for successful intervention. Key screening methods include stool-based tests, such as the fecal occult blood test (FOBT) and the fecal immunochemical test (FIT), which can be performed at home and require different levels of dietary restrictions. Other methods, such as flexible sigmoidoscopy and colonoscopy, offer visual examinations of the colon, allowing for biopsy and polyp removal if necessary.
These tests are generally recommended to begin at age fifty and vary in frequency; for instance, FOBT is performed yearly, while colonoscopy is typically recommended every ten years if no abnormalities are found. While stool tests are less invasive, visual examinations provide a more comprehensive assessment, although they carry slight risks of complications. Emphasizing early detection through these screenings can significantly improve treatment outcomes and survival rates for those at risk of colorectal cancer.
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Colorectal cancer screening
ALSO KNOWN AS: Fecal occult blood test (FOBT), guaiac-based fecal occult blood test (gFOBT), multitargeted stool DNA test with fecal immunochemical testing (MT-sDNA or FIT-DNA or sDNA-FIT), immunoassay, or immunochemical, fecal immunochemical test (FIT or iFOBT), flexible sigmoidoscopy, double-contrast barium X-ray, colonoscopy, or virtual colonoscopy
DEFINITION: Colorectal cancer screening tests are performed to detect abnormalities in the large intestine and rectum. The tests vary in accuracy, ease of performance, and invasiveness. Tests may be stool-based or visual.
Cancers diagnosed:Colorectal cancers
Why performed: Early-stage colorectal cancers do not cause symptoms. The treatment of polyps or precancerous lesions can prevent the development of cancer, and the early detection of colorectal cancer can result in more effective treatment and increased survival rates. Testing is also performed as surveillance for chronic inflammatory conditions such as Crohn's disease, ulcerative colitis, and familial polyposis.
Patient preparation: Preparation varies with the test being performed. Fecal occult blood test (FOBT) and immunoassay (or immunochemical) fecal occult blood test (iFOBT) do not require patient preparation. However, FOBT restricts the eating of red meat and the taking of aspirin, ibuprofen, or other nonsteroidal anti-inflammatory drugs (NSAIDs), except acetaminophen, for three days before the samples are taken. Flexible sigmoidoscopy, double-contrast barium X-ray, and colonoscopy require that the colon be free of all fecal material so the lining of the intestine can be visualized. This preparation necessitates taking strong laxatives the day and evening before the examination, eating a clear liquid diet the day before the examination, and not eating any food after midnight on the day of the examination. Some preparation protocols also call for a self-administered enema before the procedure.
Steps of the procedure: The FOBT, a test for the presence of blood in the feces, is the simplest test for colorectal cancer and is performed by the patient at home. It is never normal to have blood in the feces, but the presence of blood does not mean cancer. Preparation begins three days prior to the collection of a fecal sample. Patients are instructed to avoid ingesting red meat, beets, other red foods or food containing red dye, aspirin, vitamin C, or iron tablets. The collection kit contains small wooden sticks to obtain stool samples and place on the cards provided. Two samples from different parts of the stool are placed on the card provided and allowed to dry before the card is closed with a flip-over cover (similar to a matchbook). Two samples are required from three separate stool samples on three cards. The cards are then placed in an envelope enclosed with the collection kit and sent to the laboratory. This test is performed yearly, beginning at age fifty.
The fecal immunochemical test (FIT or iFOBT) also detects blood in stool from the lower intestines but requires no food or medication restrictions before sample collection, minimizing inaccurate results from poor preparation. Only a single sample is required, and it can be performed at home. There is evidence that the FIT might be more accurate at specifically detecting human blood in the stool, but if the result is positive, further testing is necessary. This test is performed yearly, beginning at age fifty. The guaiac-based fecal occult blood test (gFOBT) tests for blood using a chemical reaction. Like FIT, it can also be conducted at home, but there are many dietary restriction preparations. The multitargeted stool DNA test with fecal immunochemical testing (MT-sDNA or FIT-DNA or sDNA-FIT) tests stool for blood and DNA changes in the stool that may result from cancer or polyp cells. This test is done every three years. Cologuard is a FIT-DNA test avaliable in the United States.
The double-contrast barium enema is an X-ray of the colon and rectum following the introduction of a barium contrast material. After the colon is completely emptied, a barium sulfate solution and air are introduced through the rectum so that the outline of the colon is clear. Following the exam, the patient expels the barium solution and might experience abdominal cramping for up to twenty-four hours. This test should be done every five years unless flexible sigmoidoscopy or colonoscopy is performed.
Flexible sigmoidoscopy allows the visual examination of the rectum and lower third of the intestine with a flexible tube lighted at the end. The physician is able to see a polyp, inflammation of the intestinal walls, or other growths. Biopsies (tiny samples of abnormal tissue) can be taken for diagnosis. This test is quick and has few complications. No sedation is required. The doctor can view only the lower third of the colon, however, so polyps or precancerous lesions beyond this point cannot be seen. If signs of disease are detected, then further testing might be necessary. This test is performed every five years unless a double-contrast barium X-ray or colonoscopy has been performed.
Colonoscopy is the most invasive yet most thorough examination for colorectal cancer. A colonoscope is a flexible tube with a light and a tiny camera at the tip. The patient is usually given conscious sedation and sleeps through the procedure. The tube is introduced through the rectum and passed through the entire colon. Biopsies and removal of polyps are performed as indicated. Virtual colonoscopy uses computerized images to see the entire colon, but biopsies cannot be performed.
After the procedure: Patients have no special instructions to follow after FOBT, iFOBT, virtual colonoscopy, or sigmoidoscopy. Following a colonoscopy, which requires thirty to sixty minutes, the patient will be monitored while waking. Because sedation has been administered, the patient will need to be driven to and from the procedure. Doctors will not allow a patient to drive or go home alone. Patients are told to rest for the remainder of the day and can resume normal activities the next day. Sometimes, gas (air used during the procedure to make it easier to view the colon) is expelled for several minutes or hours following a sigmoidoscopy or colonoscopy.
Risks: The FOBT and iFOBT tests involve no risks, and risks for the double-contrast barium enema and flexible sigmoidoscopy, which require no sedation, are rare. The flexible sigmoidoscopy rarely results in small tears in the colon or rectum. The risks of colonoscopy include bleeding, the possibility of tears in the colon or rectum, and perforation of the colon or rectum. However, these are rare complications. The test should be performed at age fifty and every ten years thereafter if no polyps or other signs of disease are detected.
Results: A negative FOBT result means no blood was found in the stool samples. A positive test means that blood was found in one or more samples, and further testing will be necessary to determine the source of bleeding. FOBT should be repeated yearly but will not detect polyps or tumors that are not bleeding.
The double-contrast barium enema can miss some small polyps and cancers. Biopsy and polyp removal cannot be performed. Therefore, additional diagnostic procedures might be necessary.
Because sigmoidoscopy examines only the lower third of the colon, polyps or precancerous lesions to that point will be detected and removed. If found, additional procedures (colonoscopy) will be needed. Lesions beyond the lower third of the colon cannot be detected by sigmoidoscopy.
Colonoscopy and virtual colonoscopy are the most sensitive and thorough tests available, although some small polyps and precancerous growths still might be missed.
Bibliography
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