Does this test have other names?
Fat in stool, fecal fat stain, quantitative stool fat
What is this test?
This test measures the amount of fat in your stool.
Having too much fat in your stool is called steatorrhea. If you have too much fat in your stool, it may be a sign that food is moving through your digestive system without being broken down and absorbed properly. This is called malabsorption. Having a fecal fat test is the best way to find out if you have malabsorption.
You can develop malabsorption if:
Your intestines don't absorb food
Your pancreas doesn't make enough digestive enzymes
Your liver isn't making enough bile. Your body needs bile to break down fats for digestion.
You can have two types of fecal fat tests: qualitative and quantitative. For a qualitative test, the lab checks a single stool sample under a microscope to count the number of fat globules, or droplets. For a quantitative test, you collect stool samples over 2 to 4 days. These samples are measured to find the total amount of fat in your stool each day.
Why do I need this test?
You may need this test if you have symptoms of a disease that causes malabsorption. This test only finds out whether you have malabsorption. It doesn't diagnose a specific disease. Symptoms of malabsorption include:
Frequent loose stools
Foul-smelling, fatty stools
You may also have this test if you have already been diagnosed with malabsorption to see how well your treatment is working.
What other tests might I have along with this test?
Your healthcare provider may also order a D-Xylose absorption test to help figure out the cause of malabsorption. D-Xylose is a type of sugar.
What do my test results mean?
Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you.
A qualitative fecal fat test counts the number of fat globules in your stool. This test measures two types of fat globules: neutral fat and fatty acids. Normal results are:
Fewer than 60 neutral fat globules seen under the microscope
Fewer than 100 fatty acid fat globules seen under the microscope
Results for a quantitative fecal fat test are given in grams per 24 hours (g/24 h). Normal results are:
2 to 7 g/24 h for adults, with fat being less than 20% of the solid stool sample
Less than 1 g/24 h for an infant:
In bottle-fed babies, fat should make up 30% to 50% of the sample
In breastfed babies, fat should make up 10% to 40% of the sample
If your results are higher, it may mean you have one of these diseases:
Celiac disease (sprue)
Diseases of the pancreas
How is this test done?
This test needs a stool sample. The method of collecting a stool sample varies depending on the type of fecal fat test you need. Your healthcare provider will explain how to collect and store the samples.
Does this test pose any risks?
This test poses no known risks.
What might affect my test results?
Your results can be affected by several things. These include:
Using a rectal suppository or oily rectal cream
Swallowing castor oil or mineral oil
Not eating a balanced diet
Eating too much fiber or taking a fiber-based stool softener
Contaminating the stool sample with urine
Taking certain medicines such as orlistat
How do I get ready for this test?
Depending on the type of fecal fat test you are having, you may need to follow a special diet and not use laxatives. Your healthcare provider will let you know what to do for this test. You may have to:
Follow a diet that includes 100 to 150 grams of fat, 100 grams of protein, and 180 grams of carbohydrate for 6 days before the test and during the test
Follow a diet that has 100 grams of fat for 3 days
Stop using laxatives before and during the test
Stop eating foods high in fiber
Stop using oily rectal creams or suppositories
Infants and children will be told how much fat to eat.
Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don’t need a prescription and any illicit drugs you may use.
September 21, 2017
Clinical features and diagnosis of malabsorption. UpToDate., Mechanisms of nutrient absorption and malabsorption. UpToDate, Van Leeuwen A. Davis's Comprehensive Handbook of Laboratory and Diagnostic Tests with Nursing Implications. 2017, 7th ed.
Haldeman-Englert, Chad, MD,Taylor, Wanda L, RN, Ph.D.