A random stool collection; sometimes a 72-hour stool collection
For a 72-hour stool collection, follow your healthcare practitioner's instructions; this may include consuming 50-150 grams of fat a day in your diet for 2-3 days prior to and during the stool collection period.
This test measures the amount of fat in a stool sample. Excess fecal fat (termed steatorrhea) may be an indication that a person's digestive system is not working properly and/or that the individual has a condition affecting the digestion of food and absorption of nutrients (malabsorption).
The body digests foods in three stages: first proteins, fats, and carbohydrates are broken down, in the stomach by acid and enzymes and in the small intestines by enzymes produced by the pancreas and bile from the liver, into their component parts. They are then absorbed, primarily in the small intestines. Finally, the nutrients are transported throughout the body and used or stored.
If there are not enough pancreatic enzymes or bile available, then fat and other foods cannot be properly digested. If a condition prevents the intestines from absorbing nutrients, then they are "lost" by excretion in the stool. In both cases – improper digestion or absorption – the affected person can experience symptoms associated with malabsorption and, in severe cases, symptoms of malnutrition and vitamin deficiency. If the condition prevents the digestion and/or absorption of fats from the diet, then excess fat is present in the stool and the person may experience prolonged diarrhea with stomach pain, cramps, bloating, gas, and weight loss.
Fat in stool may be detected with the qualitative fecal fat test, which generally determines the presence or absence of excess fat. This is the simplest test for fecal fat and is performed by placing a suspension of treated or untreated stool onto a glass slide, adding a fat stain, and observing the number and size of fat globules that are present.
Quantitative measurements of fecal fat, though somewhat more precise, are less commonly performed. They require a timed stool collection and a dietary sheet to help calculate the total fat intake during the collection period, usually a 72-hour stool collection. Results are reported as the amount of fat excreted per 24 hours. A variation of the test is called the acid steatocrit, which provides a rapid but less exact measure of the amount of fat in the stool.
How is the sample collected for testing?
For a 72-hour stool collection, save all stool during the collection time period in the container(s) provided. It may be collected in a variety of ways, such as on plastic wrap, but should not be contaminated by urine, toilet water, or toilet paper. For a random sample, collect a single specimen in the same fashion.
Is any test preparation needed to ensure the quality of the sample?
For a 72-hour stool collection, follow your healthcare provider's instructions and dietary recommendations. This may include consuming a fat-controlled diet containing 50-150 grams of fat a day for 2-3 days prior to and during the stool collection period. You will also be asked to avoid certain oils and fat substitutes during the collection as these can invalidate the test result.
How is it used?
Fecal fat testing is typically ordered along with or as a follow up to other stool tests and blood tests to investigate the cause of chronic diarrhea and loose, fatty, foul-smelling stools (steatorrhea).
Stool tests may include:
- Fecal occult blood test (FOBT) – to detect blood in the stool
- O&P (Ova and Parasite) – to detect parasites
- Fecal white blood cells – to detect white blood cells in the stool
- Fecal elastase – a protein-cleaving enzyme produced and secreted by the pancreas; it is resistant to degradation by other enzymes and so is excreted and can be measured in the stool. The amount of this enzyme is reduced in pancreatic insufficiency.
- Fecal fat, qualitative – usually a suspension of stool placed on a glass slide that is treated with a special stain and examined under the microscope to detect the presence of fat droplets
Blood tests may be ordered to further investigate malabsorption symptoms and may include:
- Complete blood count (CBC) – to evaluate red and white blood cells
- Comprehensive metabolic panel (CMP) – to evaluate liver function, proteins, and electrolytes
- Celiac disease antibody tests – to detect this condition
Tests for cystic fibrosis may be performed as part of the investigation:
If the qualitative fecal fat is negative, then a 72-hour quantitative fecal fat test may be ordered. This is a better evaluation of fat digestion and absorption. There are two reasons for this:
- For the quantitative test, the person being tested is required to ingest a moderately high amount of fat per day prior to and during sample collection so their absorption ability is being "challenged."
- Fat is not released into the stool at a constant rate so the combination and mixing of the stool from a 72-hour collection gives a more accurate picture of average absorption and elimination than a single sample.
When is it ordered?
- Fatty stools that are loose and foul-smelling (steatorrhea)
- Persistent diarrhea
- Abdominal pain, cramps, bloating, and gas
- Weight loss
- Failure to thrive (in children)
If the qualitative test is negative and the healthcare provider still suspects excess fecal fat, then a quantitative 72-hour fecal fat may be ordered.
What does the test result mean?
A positive qualitative fecal fat test or an increased amount of fat in a 72-hour quantitative fecal fat test indicates that fat is likely not being absorbed normally and that the person may have impaired digestion or malabsorption.
Malabsorption is seen with a wide variety of diseases and conditions. Some causes of malabsorption include:
- Diseases affecting the intestines such as:
- Pancreatic insufficiency caused by:
- Diseases and conditions of the bile ducts and/or gallbladder
- Narrowing or blockage of the common bile duct, the main tube that carries bile from the liver and gallbladder to the intestines
Other laboratory tests used in conjunction with the fecal fat test are usually required to determine the underlying cause of fat malabsorption.
A negative qualitative fecal fat test does not necessarily rule out malabsorption so it may be followed up with a quantitative test.
In a 72-hour fecal fat test, a low level of fecal fat generally indicates that the person tested is digesting and absorbing fats normally and suggests that the symptoms being experienced are likely due to another cause.
Is there anything else I should know?
Laxatives, enemas, barium, mineral oil, fat-blocking supplements, psyllium fiber, and fat substitutes may affect test results.
Children cannot ingest as much daily fat as adults. Their test preparation will be adjusted and their 72-hour fecal fat test results will typically be reported as a percentage. This result is a "coefficient" that compares the amount of fat eaten to the amount excreted in order to evaluate the quantity of fat absorbed.
Although 72 hours is the typical sample collected for a quantitative fecal fat, a healthcare provider may sometimes ask for a 24- or 48-hour stool sample instead.
If my doctor tells me to eat 100 grams of fat a day, can I vary it between 50 and 150 grams?
You should try to follow your healthcare provider's recommendations as closely as possible. Eating a similar amount of fat each day will help ensure that the interpretation of your results is accurate. For more information on the fat content of various foods, visit the page on Food Exchange Lists by the National Heart, Lung and Blood Institute.
Can I just do the screening fecal fat test and not the 72-hour test?
If the screening test is positive, then the 72-hour test is not generally necessary. However, if it is negative, then your healthcare provider may want the additional information that the 72-hour sample provides.
Can the fecal fat test be done in my doctor's office?
On This Site
Tests: Xylose Absorption Test, Celiac Disease Antibody Tests, Comprehensive Metabolic Panel, Complete Blood Count, Fecal Occult Blood Test and Fecal Immunochemical Test, O&P, Chymotrypsin, Trypsinogen, Sweat Test, CF Mutation Panel, Stool Elastase
Elsewhere On The Web
American Gastroenterological Association: Patient Care
National Institute for Digestive Diseases Information Clearinghouse: Your Digestive System and How it Works
MedlinePlus Medical Encyclopedia: Malabsorption Syndromes