A stool analysis is a series of tests done on a stool (feces) sample to help diagnose certain conditions affecting the digestive tract. These conditions can include infection (such as from parasites, viruses, or bacteria), poor nutrient absorption, or cancer.
For a stool analysis, a stool sample is collected in a clean container and then sent to the laboratory. Laboratory analysis includes microscopic examination, chemical tests, and microbiologic tests. The stool will be checked for color, consistency, amount, shape, odor, and the presence of mucus. The stool may be examined for hidden (occult) blood, fat, meat fibers, bile, white blood cells, and sugars called reducing substances. The pH of the stool also may be measured. A stool culture is done to find out if bacteria may be causing an infection.
Why It Is Done
Stool analysis is done to:
- Help identify diseases of the digestive tract, liver, and pancreas. Certain enzymes (such as trypsin or elastase) may be evaluated in the stool to help see how well the pancreas is working.
- Help find the cause of symptoms affecting the digestive tract, such as prolonged diarrhea, bloody diarrhea, an increased amount of gas, nausea, vomiting, loss of appetite, bloating, belly pain and cramping, and fever.
- Screen for colon cancer by checking for hidden (occult) blood.
- Look for parasites, such as pinworms or Giardia.
- Look for the cause of an infection, such as bacteria, a fungus, or a virus.
- Check for poor absorption of nutrients by the digestive tract (malabsorption syndrome). For this test, all stool is collected over a 72-hour period and then checked for fat (and sometimes for meat fibers). This test is called a 72-hour stool collection or quantitative fecal fat test.
How To Prepare
Many medicines can change the results of this test. You will need to avoid certain medicines depending on which kind of stool analysis you have. You may need to stop taking medicines such as antacids, antidiarrheal medicines, antiparasite medicines, antibiotics, laxatives, or nonsteroidal anti-inflammatory drugs (NSAIDs) for 1 to 2 weeks before you have the test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
Be sure to tell your doctor if you have:
- Recently had an X-ray test using barium contrast material, such as a barium enema or upper gastrointestinal series (barium swallow). Barium can interfere with test results.
- Traveled in recent weeks or months, especially if you have traveled outside the country. This helps your doctor look for the parasites, fungi, viruses, or bacteria that may be causing a problem.
If your stool is being tested for blood, you may need to avoid certain foods for 2 to 3 days before the test. This depends on what kind of stool test you use. And do not do the test during your menstrual period or if you have active bleeding from hemorrhoids. If you aren't sure about how to prepare, ask your doctor.
Do not use a stool sample for testing that has been in contact with toilet bowl cleaning products that turn the water blue.
How It Is Done
You will be given stool collection kits to use each day. You may need to collect more than one sample. Follow the directions in the kits. The contents may be different.
To collect the samples:
- Urinate before you collect the stool so that you don't get any urine in the stool sample.
- Follow the directions for putting the sample collection container on the toilet.
- Pass stool (have a bowel movement) into the collection container.
- Either solid or liquid stool can be collected.
- If you have diarrhea, a large plastic bag taped to the toilet seat may make the collection process easier. The bag is then placed in a plastic container.
- Do not collect the sample from the toilet bowl.
- Do not mix toilet paper, water, or soap with the sample.
- Place the lid on the bottle, and label it with your name and the date the stool was collected. Use one bottle for each day's collection. Collect a sample only once a day unless your doctor gives you other directions.
- Flush the remaining stool down the toilet.
- Seal the collection container in a bag and throw it away.
- Wash your hands.
Your doctor will tell you when to return the sample to the lab.
How long the test takes
The test will take a few minutes each time you take a sample.
How It Feels
There is no pain while collecting a stool sample. If you are constipated, straining to pass stool may be painful.
If your health professional uses a rectal swab to collect the sample, you may feel some pressure or discomfort as the swab is inserted into your rectum.
Any stool sample may contain germs that can spread disease. Make sure to carefully wash your hands and use careful handling techniques to avoid spreading infection.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
A stool analysis may check values for pH, reducing factors, and fat.
The stool appears brown, soft, and well-formed in consistency.
The stool is shaped like a tube.
The stool is black, red, white, yellow, or green.
The stool is liquid or very hard.
There is too much stool.
The stool contains blood, mucus, pus, undigested meat fibers, harmful bacteria, viruses, fungi, or parasites.
The stool contains low levels of enzymes, such as trypsin or elastase.
Many conditions can change the results of a stool analysis. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.
- High levels of fat in the stool may be caused by diseases such as pancreatitis, sprue (celiac disease), cystic fibrosis, or other disorders that affect the absorption of fats.
- The presence of undigested meat fibers in the stool may be caused by pancreatitis.
- A low pH may be caused by poor absorption of carbohydrate or fat. Stool with a high pH may mean inflammation in the intestine (colitis), cancer, or antibiotic use.
- Blood in the stool may be caused by bleeding in the digestive tract.
- White blood cells in the stool may be caused by inflammation of the intestines, such as ulcerative colitis, or a bacterial infection.
- Rotaviruses are a common cause of diarrhea in young children. If diarrhea is present, testing may be done to look for rotaviruses in the stool.
- High levels of reducing factors in the stool may mean a problem digesting some sugars.
- Low levels of reducing factors may be caused by sprue (celiac disease), cystic fibrosis, or malnutrition. Medicine such as colchicine (for gout) or birth control pills may also cause low levels.