At a Glance
Why Get Tested?
To detect and measure excess fat in the stool; to help diagnose conditions causing malabsorption
When to Get Tested?
When a person has symptoms of malabsorption such as persistent diarrhea and fatty stools
A random stool collection; sometimes a 72-hour stool collection
Test Preparation Needed?
For a 72-hour stool collection, follow your doctor's instructions. Consume 50-150 grams of fat a day in your diet for 2-3 days prior to and during the stool collection period.
The Test Sample
What is being tested?
This test measures the amount of fat in a stool sample. Excess fecal fat (termed steatorrhea) is an indicator of impaired digestion and/or 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, and finally the nutrients are transported throughout the body and used or stored.
If there is not enough bile or pancreatic enzymes 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 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.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
For a 72-hour stool collection, consume 50-150 grams of fat a day for 2-3 days prior to and during the stool collection period. The fat should be long-chain triglycerides (such as corn or olive oil, not butter). Follow the doctor's instructions and dietary recommendations.
Ask a Laboratory Scientist
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
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Dugdale, D. (Updated 2010 July 7). Malabsorption. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000299.htm. Accessed June 2011.
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