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Fecal Fat

Does this test have other names?

Fat in stool, fecal fat stain, quantitative stool fat, qualitative 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 2 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 usually over a period of 3 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 greasy, loose stools in large amounts

  • Indigestion

  • Gas

  • Cramps

  • Foul-smelling, fatty stools

  • Unintentional weight loss

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. Your provider may also order imaging tests such as an upper endoscopy or X-rays of your small intestine to find out the cause.

What do my test results mean?

Test results may vary depending on your age, sex, 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 2 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 a baby:

    • 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 1 of these diseases:

  • Cystic fibrosis

  • Crohn disease

  • Celiac disease (sprue)

  • Malnutrition

  • Enteritis

  • Whipple disease

  • Diseases of the pancreas

  • Pancreatic surgery

How is this test done?

This test is done with 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 has 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

  • Urine in the stool sample

  • 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

Babies and children will need to have a specific amount of fat in their daily diet before the test.

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 illegal drugs you may use.

Online Medical Reviewer: Chad Haldeman-Englert MD
Online Medical Reviewer: Maryann Foley RN BSN
Online Medical Reviewer: Raymond Turley Jr PA-C
Date Last Reviewed: 8/1/2020
© 2000-2020 The StayWell Company, LLC. 800 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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