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, weight (volume), 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 determine how well the pancreas is functioning.
- Help find the cause of symptoms affecting the digestive tract, including prolonged diarrhea, bloody diarrhea, an increased amount of gas, nausea, vomiting, loss of appetite, bloating, abdominal pain and cramping, and fever.
- Screen for colon cancer by checking for hidden (occult) blood.
- Look for parasites, such as pinworms or Giardia lamblia.
- 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 the fat and meat fibers. This test is called a 72-hour stool collection or quantitative fecal fat test.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean.
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, enemas, 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:
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. If you aren't sure, ask your doctor.
Do not do the test during your menstrual period or if you have active bleeding from hemorrhoids. Also, do not test a stool sample that has been in contact with toilet bowl cleaning products that turn the water blue.
How It Is Done
Stool samples can be collected at home, in your doctor's office, at a medical clinic, or at the hospital. If you collect the samples at home, you will be given stool collection kits to use each day. Each kit contains applicator sticks and two sterile containers.
You may need to collect more than one sample over 1 to 3 days. Follow the same procedure for each day.
Collect the samples as follows:
- Urinate before collecting the stool so that you do not get any urine in the stool sample.
- Put on gloves before handling your stool. Stool can contain material that spreads infection. Wash your hands after you remove your gloves.
- Pass stool (but no urine) into a dry container. You may be given a plastic basin that can be placed under the toilet seat to catch the stool.
- 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.
- If you are constipated, you may be given a small enema.
- 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 container and label it with your name, your doctor's name, and the date the stool was collected. Use one container for each day's collection, and collect a sample only once a day unless your doctor gives you other directions.
Take the sealed container to your doctor's office or the laboratory as soon as possible. You may need to deliver your sample to the lab within a certain time. Tell your doctor if you think you may have trouble getting the sample to the lab on time.
If the stool is collected in your doctor's office or the hospital, you will pass the stool in a plastic container that is inserted under the toilet seat or in a bedpan. A health professional will package the sample for laboratory analysis.
You will need to collect stool for 3 days in a row if the sample is being tested for quantitative fats. You will begin collecting stool on the morning of the first day. The samples are placed in a large container and then refrigerated.
You may need to collect several stool samples over 7 to 10 days if you have digestive symptoms after traveling outside the country.
Samples from babies and young children may be collected from diapers (if the stool is not contaminated with urine) or from a small-diameter glass tube inserted into the baby's rectum while the baby is held on an adult's lap.
Sometimes a stool sample is collected using a rectal swab that contains a preservative. The swab is inserted into the rectum, rotated gently, and then withdrawn. It is placed in a clean, dry container and sent to the lab right away.
A stool analysis is a series of tests done on a stool (feces) sample to help diagnose certain conditions affecting the digestive tract.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Stool analysis test results usually take at least 1 to 3 days.
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.
|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.
|The pH of the stool is less than 7.0 or greater than 7.5.
|The stool contains more than 0.5 g/dL or more than 27.8 mmol/L of sugars called reducing factors; 0.25–0.5 g/dL and 13.9–27.8 mmol/L is considered borderline.
|The stool contains more than 7 g/24h of fat (if your fat intake is about 100 g a day).
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.
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
- Taking medicines such as antibiotics, antidiarrheal medicines, barium, bismuth, iron, ascorbic acid, nonsteroidal anti-inflammatory drugs (NSAIDs), and magnesium.
- Contaminating a stool sample with urine, menstrual blood, bleeding hemorrhoids, or chemicals found in toilet paper and paper towels.
- Exposing the stool sample to air or room temperature or failing to send the sample to a laboratory within 1 hour of collection.
What To Think About
- Stool may be checked for hidden (occult) blood..
- A stool culture is done to find the cause of an infection, such as bacteria, a virus, a fungus, or a parasiteA bowel transit time test is done to help find the cause of abnormal movement of food through the digestive tract.
- The D-xylose absorption test is done to help diagnose problems that prevent the small intestine from absorbing nutrients in food. This test may be done when symptoms of malabsorption syndrome (such as chronic diarrhea, weight loss, and weakness) are present.
- A stool analysis to measure trypsin or elastase is not as reliable as the sweat test to detect cystic fibrosis.
The color of stool normally is brown. The reason for the brown color is the presence of bile in the stool. Bile is made by the liver, concentrated and stored in the gallbladder, and secreted into the intestine to aid in the digestion of food. Depending on the amount of bile it contains, the normal stool color can range in color from light yellow to almost black.
Bile secreted from the gallbladder into the intestine is a very dark green liquid made up of many chemicals, one of which is bilirubin. When red blood cells are destroyed naturally in the body, the hemoglobin, a protein inside the red blood cells that carries oxygen, is modified in the liver. The by-product of this process is bilirubin, and the liver secretes the bilirubin into bile.
As the bile travels through the intestines, it can undergo further chemical changes, and its color can also change. For example, if the traveling time through the intestine is too rapid, then bile won't have the time to go through additional color changes and the stool color may be close to green.
The color of stool can change for other reasons as well. Many changes in stool color may not be of much importance, especially if the change happens once and is not consistent from one stool to the next. Sudden major changes in stool color that persist may suggest an underlying medical problem. Furthermore, gradual but persistent changes in stool color also can signify medical problems.
Some of the important colors of stool that can signify problems include:
- pale, and
Stool Color Changes Causes
Stool color can change for a variety of reasons. Some stool color changes may signify an underlying medical condition, and others may be due to ingestion of food or medications.
Black Tarry, Sticky Stools
Bleeding in the stomach or the intestines can change the color of stool. If bleeding occurs in the stomach or the upper part of the small intestine, the stool may turn black and sticky, described medically as black, tarry stool. Generally, black, tarry stool also is foul-smelling. This change in color and consistency occurs because of chemical reactions to blood within the intestine that are caused by digestive enzymes within the intestines.
Maroon or Red Stools
If the bleeding originates from lower parts of the intestines, blood may not come into prolonged contact with digestive enzymes because of the short distance from the site of bleeding to the rectum. Moreover, large amounts of blood within the intestines speeds up transit of stool so that there is less time for the changes to take place. The stool in this type of bleeding may be dark red or maroon in color. Beets, other red vegetables, and red food dyes also can turn the stool color red.
Black Stools (Not Sticky, No Odor)
Other causes of black stool are iron pills or bismuth-containing medications (such as, bismuth subsalicylate or Pepto Bismol). If the stool color is dark because of any of these medications, it is typically not sticky in texture and is not foul-smelling .
Gray or Clay-Colored Stool
Stool can be gray or clay-colored if it contains little or no bile. The pale color may signify a condition (biliary obstruction) where the flow of bile to the intestine is obstructed, such as, obstruction of bile duct from a tumor or stone.
Stool that is yellow may suggest presence of undigested fat in the stool. This can happen as a result of diseases of pancreas that reduce delivery of digestive enzymes to the intestines, such as chronic pancreatitis (long standing inflammation and destruction of the pancreas usually due to alcohol abuse) or obstruction of the pancreatic duct that carries the enzymes to the intestines (most commonly due to pancreatic cancer). The digestive enzymes released from the pancreas and into the intestines are necessary to help digest fat and other components of food (proteins, carbohydrates) in the intestines so that they can be absorbed into the body. If the pancreas is not delivering enzymes into the intestines, then components of food, especially the fat, can remain undigested and unabsorbed. The stool containing the undigested fat may appear yellowish in color, greasy, and also smell foul.
Stool Color Changes Symptoms
The symptoms associated with changes in the color of stool generally correspond to the underlying cause (although the presence of large amounts of blood alone may lead to diarrhea and possibly cramping). In many instances, there may not be any symptoms associated with changes in the color of stool.
Bleeding from the gastrointestinal tract (esophagus, stomach, small intestine, large intestine) leading to red, maroon, or black tarry stools may be without any symptoms at all or may have accompanying symptoms of
- abdominal pain due to the underlying cause of the bleeding, for example, an ulcer;
- nausea, vomiting of blood, diarrhea, and cramping due to the presence of blood in the stomach and/or intestines; and
- weakness, lightheadedness, and dizziness, due to the loss of blood from the body.
Persistently gray or clay-colored stools suggest some type of obstruction to the flow of bile. Obstruction caused by gallstones usually is associated with pain on the right side of the abdomen. However, cancer of the bile duct or cancer of the head of pancreas, which also can cause obstruction to the flow of bile by pressing on the bile duct, may not be associated with abdominal pain unless the tumor is large. The obstruction to the flow of bile causes backup of bile into the blood resulting in yellowness of skin and eyes that is referred to as jaundice.
Yellow stool as a result of undigested fat also may occur with no symptoms. If present, the most common symptom associated with yellow stool will be abdominal pain as a result of chronic pancreatitis, tumor of the pancreas, or obstruction of the pancreatic duct
Exams and Tests
The evaluation of changes in stool color typically begins with a thorough physical examination and personal medical history. The doctor may ask about intake of alcohol, smoking, and other habits. Family history of any cancers, particularly of the liver or pancreas or bleeding problems may be helpful. A review of medications that may affect the color of stool, including over-the-counter (OTC) medications, also is important. Any changes in bowel habits (constipation, diarrhea, and change in frequency) or any pertinent symptoms (pain with or without eating, nausea, vomiting, weight loss, etc.) can provide valuable clues in evaluating the underlying causes of changes in stool color.
Diagnostic testing to find the cause of changes in stool color typically start with simple blood tests including complete blood count (CBC), chemistries, liver enzymes (comprehensive metabolic panel or CMP or SMA 19), and blood clotting (coagulation). These tests can demonstrate anemia, liver disease, gallbladder disease, or other underlying conditions that may be responsible for the changes in stool color. Pancreatic enzymes--amylase and lipase--also can be measured to determine if pancreatic disease is present.
If bleeding from the stomach or intestines is suspected but the stool is not visibly black, red or maroon, occult blood (a small amount of blood that does not cause the color of stool to change much) can be sought by testing the stool directly for blood with a dye (fecal occult blood test or FOBT). This test relies on a chemical reaction between a solution (called guaiac) and hemoglobin in a sample of stool. In the presence of hemoglobin, the drop of solution will turn the stool sample (smeared onto a special paper which reacts chemically with the solution) blue. This test is part of the recommendation for screening for colon cancer, although in clinical practice, it is often used to determine if any bleeding is occurring in the gastrointestinal system. In addition to the test using guaiac, there is an immunological test for blood in the stool that uses an antibody to hemoglobin to detect the blood.
Methods to evaluate a change in the color of stool are upper gastrointestinal endoscopy (esophago-gastro-duodenoscopy or EGD) and colonoscopy. These tests are done by gastroenterologists to look inside the esophagus and stomach (EGD) and the colon (colonoscopy) with a video camera to detect the source of the bleeding or other abnormality that may explain the change in stool color. If necessary, biopsies can be taken with these techniques.
More advanced endoscopic testing to look for obstruction of the biliary or pancreatic ducts is called an endoscopic retrograde cholangio-pancreatography or ERCP. This test is performed like an EGD except that during the test dye is injected into the bile and pancreatic ducts to look with X-rays for obstruction of the ducts.
Other imaging studies sometimes are necessary in order to find the cause of the change in stool color. Computerized tomography (CT scan) is ordered frequently by physicians if the change in stool color is believed to be related to underlying cancer, pancreatic disease, or obstructive conditions of the bile ducts and gallbladder. Ultrasound of the abdomen is a frequently used, relatively inexpensive and reliable test to evaluate for gallstones or blockage of the gallbladder. Magnetic resonance imaging (MRI) of the abdomen sometimes is done to look more closely at any obstructive disease of the biliary or pancreatic ducts