Fecal Fat
- Also Known As:
- Qualitative or Quantitative Stool Fat
- Stool Lipids
- 72 Hour Fecal Fat
- Fat Stain Oil Red O
- Fat
- Feces
- Formal Name:
- Fat
- Fecal Qualitative or Quantitative

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.At a Glance
Why Get Tested?
To detect and measure excess fat in the stool; to help diagnose conditions causing malabsorption, which is difficulty digesting food and absorbing nutrients
When To Get Tested?
When you have symptoms of malabsorption, such as persistent diarrhea and fatty stools
Sample Required?
A random stool collection; sometimes a 72-hour stool collection
Test Preparation Needed?
For a 72-hour stool collection, follow the instructions from the lab performing the test or your health practitioner. 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.
What is being tested?
This test measures the amount of fat in a stool sample. Excess fecal fat (termed steatorrhea) may be an indication that your digestive system is not working properly and/or that you have a condition affecting the digestion of food and absorption of nutrients, also called malabsorption.
The body digests foods in stages: 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 and cannot be efficiently absorbed. If a condition prevents the intestines from absorbing nutrients, then they are eliminated in the stool. In both cases – improper digestion or absorption – you can experience symptoms associated with malabsorption and, in severe cases, symptoms of malnutrition and vitamin deficiency. If the condition prevents you from digesting and absorbing fats from the diet, then excess fat is present in the stool and you may experience persistent diarrhea with stools that are loose and foul-smelling (steatorrhea).
Fat in stool may be detected with the qualitative fecal fat test, which generally determines the presence or absence of excess fat. This test 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. It should be performed by an experienced professional.
Quantitative measurements of fecal fat, though somewhat more accurate, are less commonly performed. However, they are considered the gold standard. 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 eliminated in stool per day (24 hours).
Another quantitative test is called the acid steatocrit, which provides a rapid but less exact measure of the amount of fat in the stool. It is a less complicated test that can be used on a random stool sample.
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. You may also be asked to discontinue using exogenous pancreatic supplements if you are using any.
Common Questions
View Sources
Sources Used in Current Review
(© 2020). Fat, Feces. Mayo Clinic Mayo Medical Laboratories. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/8310. Accessed November 2020.
Dugdale, D. (Updated December 3, 2020). Malabsorption. MedlinePlus Medical Encyclopedia. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000299.htm. Accessed December 2020.
Delgado, J. and Grenache, D. (November 2017). Malabsorption. ARUP Consult. Available online at https://arupconsult.com/content/malabsorption. Accessed December 2020.
Azer SA, Sankararaman S. Steatorrhea. [Updated 2020 May 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available online at https://www.ncbi.nlm.nih.gov/books/NBK541055/. Accessed December 2020.
Sources Used in Previous Reviews
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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.
Delgado, J. and Grenache, D. (Updated 2010 November). Malabsorption. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/Topics/Malabsorption.html?client_ID=LTD. Accessed June 2011.
Ruiz, A. (Revised 2008 January). Malabsorption. Merck Manual for Healthcare Professionals [On-line information]. Available online at http://www.merckmanuals.com/professional/sec02/ch017/ch017a.html?qt=malabsorption&alt=sh. Accessed June 2011.
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Ruiz, A. (2014 May Revised). Overview of Malabsorption. Merck Manual Professional Version [On-line information]. Available online at http://www.merckmanuals.com/professional/SearchResults?query=malabsorption. Accessed on 10/08/15.
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