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 juice
Your gallbladder isn't making enough bile, which you need to absorb fats
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 two to four 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:
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 doctor 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?
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
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:
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 percent 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 percent of the sample
In breastfed babies, fat should make up 10 to 40 percent 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 requires a stool sample. The method of collecting a stool sample varies depending on the type of fecal fat test you need. Your doctor 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, including:
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
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 doctor 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 six days before the test and during the test
Follow a diet that has 100 grams of fat for three 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.
- Bass, Pat F. III, MD, MPH
- Stump-Sutliff, Kim, RN, MSN, AOCNS