To detect and measure excess fat in the stool; to help diagnose conditions causing malabsorption
Fecal Fat
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
This article was last reviewed
on
This article waslast modified
on January 21, 2021.
At a Glance
Why Get Tested?
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 healthcare 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.
Accordion Title
Common Questions
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How is the test 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 immunochemical test and fecal occult blood test – to detect blood in the stool
- O&P (ova and parasite exam) – to detect parasites
- Fecal white blood cells – to detect white blood cells in the stool; excess white blood cells can be a sign of gut infection or inflammation.
- 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. Pancreatic insufficiency in cystic fibrosis leads to maldigestion and malabsorption:
A qualitative fecal fat may be ordered as a screening test. If it is positive for excess fecal fat, then a quantitative test is generally not necessary.
If the qualitative fecal fat is negative and your healthcare provider still suspects excess fecal fat, 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, you are required to include a moderately high amount of fat in your diet per day prior to and during sample collection so your ability to absorb fat "challenged."
- Fat is not released into the stool at a constant rate so results from collecting stool over 72 hours gives a more accurate picture of average absorption and elimination than a single sample.
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When is it ordered?
A fecal fat test is primarily ordered when you have signs and symptoms of malabsorption such as:
- Fatty stools that are loose and foul-smelling (steatorrhea)
- Persistent diarrhea
- Abdominal pain, cramps, bloating, and gas
- Weight loss
- Failure to thrive (in children)
These symptoms may or may not be accompanied by other indicators such as fatigue, anemia and/or specific nutritional deficiencies in, for example, iron or vitamin B12.
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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 you may have impaired digestion or malabsorption. (Quantitative results are typically reported as grams per day or g/d.)
Malabsorption is seen with a wide variety of diseases and conditions. Examples include:
- Diseases affecting the intestines such as:
- Infections, including parasitic, bacterial or viral
- Celiac disease
- Inflammatory bowel disease (Crohn disease, ulcerative colitis)
- Pancreatic insufficiency caused by:
- Chronic pancreatitis
- Pancreatic cancer
- Cystic fibrosis (affects the function of the pancreas)
- Shwachman-Diamond Syndrome
- Gallbladder diseases and conditions of the bile ducts
- Cancer
- 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.
In a 72-hour fecal fat test, a low level of fecal fat generally indicates that you are digesting and absorbing fats normally and suggests that the symptoms being experienced are likely due to another cause.
- Diseases affecting the intestines such as:
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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.
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Can I just do the screening fecal fat test and not the 72-hour test?
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Can the fecal fat test be done in my doctor's office?
The qualitative fecal fat test may be done in a healthcare provider's office if it has the proper stain and equipment. The quantitative test is not performed by all labs. You sample may be sent to a reference laboratory for testing.
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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 eliminated 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-hour or 48-hour stool sample instead.