A stool test checks what is in your bowel movements to look for signs of disease or infection
A stool test, also called a fecal test, is a laboratory examination of a sample from your bowel movement. Your doctor sends the sample to a lab where technicians look for blood, bacteria, parasites, viruses, or other substances that might signal a health problem. The test does not hurt and does not require any procedure — you collect the sample at home in a container your doctor provides, then return it to the lab or your doctor's office.
Stool tests are one of the most common screening tools in medicine. They can detect colorectal cancer, infections, digestive disorders, and other conditions. Some tests look for a single thing — like blood in the stool — while others examine the sample for multiple problems at once.
Key Takeaways
- You collect a stool sample at home using a container provided by your doctor, then return it to a lab or medical office.
- Different stool tests look for different things: blood, bacteria, parasites, viruses, or signs of cancer.
- The most common stool test for people over 45 is the fecal immunochemical test (FIT), which screens for colorectal cancer.
- Results usually come back within one to two weeks, though some tests take longer.
- A positive result does not mean you have a disease — it means your doctor needs to do more testing to find out what is causing the result.
Types of stool tests and what they screen for
The fecal immunochemical test (FIT) is the most widely used stool test for colorectal cancer screening in people over 45. It detects microscopic blood in the stool that you cannot see with your eyes. If blood is present, your doctor will likely order a colonoscopy to look inside your colon and find the source.
The guaiac fecal occult blood test (gFOBT) is an older version of the FIT that also looks for hidden blood. It works slightly differently and is less commonly ordered now, but some doctors still use it.
A stool culture looks for bacterial infections like salmonella or E. coli. Your doctor orders this when you have severe diarrhea or other signs of a bacterial infection.
A parasitology test searches for parasites and their eggs in the stool. This is ordered when someone has traveled to areas where parasitic infections are common or has symptoms like persistent diarrhea and weight loss.
A fecal fat test measures the amount of fat in your stool over several days. It helps doctors diagnose malabsorption disorders — conditions where your body cannot absorb nutrients properly from food.
How to collect a stool sample
Your doctor will give you a kit with clear instructions and a sterile container. Most kits include a small brush or spatula to collect the sample. You collect the sample in the toilet or a clean container, then use the tool to transfer a small amount to the provided container. The sample only needs to be about the size of a hazelnut.
Follow the instructions on your kit carefully. Some tests require you to collect samples on multiple days — usually two or three separate bowel movements — because results are more accurate when the lab has more than one sample. If your kit includes a preservative liquid, mix it with the sample as directed.
Label the container with your name and the date, then store it in the refrigerator if you cannot return it to your doctor's office or the lab right away. Most samples should be returned within 24 hours, though some kits allow longer storage. Check your instructions or call your doctor's office if you are unsure.
What happens after you return your sample
The lab receives your sample and performs the test your doctor ordered. The time it takes to get results depends on the type of test. A FIT usually takes one to two weeks. A stool culture can take three to five days or longer because bacteria need time to grow. A parasitology test may take several days to a week.
Your doctor's office will contact you with the results. If the result is negative, it means the test did not find what it was looking for — which is usually good news. If the result is positive, your doctor will call to discuss what it means and what the next step should be.
What a positive result means and what comes next
A positive stool test does not mean you have cancer or a serious disease. It means the test found something that needs further investigation. For example, a positive FIT means blood was detected in your stool, but blood can come from many sources — hemorrhoids, a small tear in the lining of your colon, an infection, or a polyp.
If your FIT is positive, your doctor will almost certainly order a colonoscopy, a procedure where a doctor looks inside your colon with a small camera. This is the only way to see what is causing the blood and to remove any polyps or take a tissue sample if needed.
If a stool culture comes back positive for bacteria, your doctor may prescribe antibiotics or other treatment depending on which bacteria was found and how severe your symptoms are.
If a parasitology test is positive, your doctor will prescribe medication to kill the parasite. The type of medication depends on which parasite was found.
Preparing for a stool test
Most stool tests require little to no preparation. You do not need to fast or change your diet before a FIT or stool culture. However, some older versions of the fecal occult blood test (gFOBT) do require dietary changes for a few days before collection — your doctor will tell you if this applies to you.
If you are taking certain medications, tell your doctor before the test. Some medications like aspirin or blood thinners can affect the results of a fecal occult blood test. Your doctor may ask you to stop taking them for a few days before collection.
If you have diarrhea or constipation, let your doctor know. Some tests work better when your bowel movements are normal, and your doctor may ask you to wait a few days or reschedule.
Reasons your doctor might order a stool test
Your doctor may order a FIT as part of routine colorectal cancer screening if you are 45 or older. Some guidelines recommend starting at 50, and some at 40 if you have a family history of colorectal cancer — ask your doctor what is right for you.
A stool culture is ordered when you have severe diarrhea that lasts more than a few days, especially if you have fever, bloody stools, or recently took antibiotics.
A parasitology test is ordered if you have chronic diarrhea, unexplained weight loss, or have traveled to a country where parasitic infections are common.
A fecal fat test is ordered when your doctor suspects malabsorption — when you have chronic diarrhea, weight loss, or fatty stools and your doctor wants to know if your body is absorbing fat from food properly.
Frequently Asked Questions
Is a stool test embarrassing or uncomfortable?
No. You collect the sample in private at home, and the sample size is very small. Many people feel relieved that screening for colorectal cancer does not require a procedure. The only discomfort some people report is mild anxiety about handling the sample, but the process is straightforward and the container is designed to be straightforward to use.
What if I cannot collect the sample or I miss the important date to return it?
Call your doctor's office right away. They can provide a new kit and give you a new important date. If your sample sat at room temperature for too long, it may not be usable, and the lab will let your doctor know. Do not guess about timing — ask your doctor's office.
Can I use a stool sample from a diaper or a pet's litter box?
No. The sample must come from your own bowel movement and be collected in the sterile container your doctor provides. Samples from diapers, litter boxes, or other sources will contaminate the test and give false results.
Do I need a colonoscopy if my stool test is negative?
Not necessarily. A negative FIT means no blood was detected, which is reassuring. However, a negative stool test does not rule out all colorectal cancers — some cancers do not bleed. Your doctor will tell you when to repeat the test and whether a colonoscopy is needed based on your age, symptoms, and risk factors.
How often should I have a stool test?
This depends on the type of test and your health history. A FIT for colorectal cancer screening is typically done every one to two years if negative, though some guidelines recommend every year. Your doctor will tell you the right schedule for you based on your age and risk factors.