About the Test
Purpose of the stool DNA test
The purpose of the stool DNA test is to check for changes in DNA and blood in the stool that cannot be seen with the naked eye. The stool DNA test is one type of test used for colorectal cancer screening. Screening refers to checking for disease when no signs or symptoms are present. Regular colorectal cancer screenings reduce the risk of death and disease caused by colon or rectal cancer.
What does the stool DNA test measure?
The stool DNA test detects DNA changes in cells that are shed from abnormal growths called polyps and cancerous tumors in the colon and rectum.
As new cells are formed in the colon, old cells are cast off and pass into the stool every day. This is a normal process. When precancerous polyps or cancer are present, abnormal cells from the tumor also shed into the stool. The stool DNA test detects these abnormal cells by looking for genetic mutations in the cells. The presence of cells with DNA changes or hidden blood in the stool may be an indication of colon cancer or precancerous polyps.
When should I get a stool DNA test?
The US Preventive Services Task Force (USPSTF) recommends screening for colorectal cancer between the ages of 45 to 75 years. Screening may begin earlier for people who are at an increased risk of developing colorectal cancer.
The stool DNA test is typically recommended every 1 to 3 years for people with an average risk of colon or rectal cancer. An average risk of colon cancer includes anyone aged 45 years or older without symptoms. Other important factors that can affect whether the stool DNA test is recommended include: a prior diagnosis of colorectal cancer or colon polyps, a family history of colon cancer or specific familial genetic disorders, inflammatory bowel disease, and other medical conditions.
Stool DNA testing is one of a number of different tests available to screen for colorectal cancer. If you have an increased risk of colorectal cancer, a colonoscopy is usually recommended as a better screening test option than a stool DNA test. Colonoscopy is the most thorough way to view the colon and allow for the removal of colon polyps and growths that may lead to cancer.
Finding a stool DNA Test
How to get tested
Currently, the only stool DNA test approved by the US Food and Drug Administration (FDA) is called Cologuard. Cologuard detects multiple gene mutations and includes a fecal immunochemical test (FIT). In order to receive this at-home stool DNA kit, you must have a prescription from your doctor.
Can I take the stool DNA test at home?
After your doctor orders your stool DNA test, the kit is usually mailed directly to you. You collect the sample at home and either return the kit to your doctor’s office or mail it to the lab for testing. The testing kit contains a sample container, a tube, preserving liquid, mailing labels, and instructions on how to collect the sample at home.
How much does the stool DNA test cost?
The cost of a stool DNA test will depend on whether you have medical insurance. Stool DNA testing is significantly more expensive than other stool-based cancer screening tests such as the FIT alone and the fecal occult blood test (FOBT). However, some types of insurance cover the full cost of a stool DNA test if you meet the criteria for coverage.
You can check with your insurance company to learn more about what your plan covers and whether you are responsible for any out-of-pocket costs such as copays or deductibles.
Taking the stool DNA Test
Stool DNA testing requires collecting an entire bowel movement. The test is done at home and you do not need to make any changes to your diet or medications before producing a sample. The stool DNA test does not require bowel preparation such as using a laxative, any anesthesia or sedation, or transportation to and from a hospital or clinic.
Before the stool DNA test
Read the instructions carefully that are included with your test kit. It’s important to use a typical bowel movement. Do not collect the sample if you are experiencing diarrhea, rectal bleeding (such as from hemorrhoids), or if you are menstruating. Collect your sample only when it is possible to mail it to the lab within 24 hours. The stool sample must reach the lab within 3 days.
During the stool DNA test
Collecting a stool sample for stool DNA testing involves the following steps:
- Read all instructions carefully and prepare the area to collect your sample.
- When you are ready to take a bowel movement, use the brackets provided in the test kit and attach the sample container to your toilet seat.
- Use the toilet for your bowel movement, being careful to not let urine or toilet paper get into the sample container.
- Remove the sample container with your bowel movement and place on a flat surface.
- Collect and place a small sample of stool into the tube provided, securing the lid tightly.
- Pour the preserving liquid into the large sample container and secure the lid tightly. If the liquid touches your skin or eyes, wash the area with water.
- Label both the tube and the sample container according to the test kit instructions.
- Place the tube and the sample container into the box provided and mail the box within 24 hours to the lab. If you need to store the box prior to mailing, be sure to store it at room temperature and away from direct sunlight or heat.
After the test
After the stool DNA test, you can resume your usual activities. There are no risks involved in using an at-home stool DNA test.
Stool DNA Test Results
Receiving test results
The turnaround time for lab test results is typically within two weeks. Your test results are sent to your doctor who can share them with you and answer any questions you may have.
Interpreting test results
Stool DNA test results are either positive or negative. A positive result means that abnormal DNA and/or blood were detected in the stool. Follow-up testing is important. If the stool DNA test is positive, a colonoscopy is usually advised for further evaluation.
A negative test result means that abnormal DNA and/or blood were not detected in the stool sample.
Are test results accurate?
Routine screening with stool DNA testing has been shown to help detect colorectal cancer early. However, false positives and false negatives can occur. A positive test result does not necessarily mean you have cancer. Alternatively, a negative test result can occasionally miss blood or DNA changes in the stool sample.
False positive results occur when results are positive but the person does not really have colorectal cancer or a growth that may become cancer. For the stool DNA test, a false positive result can occur if traces of blood from hemorrhoids are found in the stool, but the person does not actually have colorectal cancer or polyps.
False negative results occur when results are negative but the person actually has colorectal cancer or a growth that may become cancer. A false negative result can occur when someone has intermittent bleeding from a cancerous or precancerous lesion in the colon. The particular stool sample may have contained no blood or DNA markers, but if a different stool sample were tested, it would detect these abnormalities.
It is essential to follow all of the instructions carefully during testing in order to reduce the risk of inaccurate results. You can talk with your doctor about any questions you have about your specific test results.
Do I need follow-up tests?
If blood and/or abnormal DNA are found in your stool, additional testing is usually recommended in order to determine the cause and location of the bleeding.
The most common follow-up test to a positive stool DNA test is a colonoscopy. The colonoscopy is a procedure to view the entire length of the colon and rectum. This test allows the doctor to remove any suspicious areas or growths with small surgical tools.
Comparing the stool DNA test with the FIT and the FOBT
The stool DNA test, the fecal immunochemical test (FIT), and the fecal occult blood test (FOBT) are all types of stool-based tests that can be used for colorectal cancer screening. Each of these stool-based tests have been shown to improve early detection of colorectal cancer, but they each also carry different benefits and drawbacks.
All three of these stool-based tests can be performed at home and require obtaining a stool sample. However, there are some key differences between these tests:
| Stool-Based Cancer Screening Tests | ||
|---|---|---|
| Test Name | Screening Interval | Test Considerations |
| Stool DNA | Every 1-3 years |
|
| FIT | Every year |
|
| FOBT | Every year |
|
Your doctor can discuss whether stool-based colorectal cancer screening is right for you and which test may be the best fit for your situation.
