Test Catalog

Test ID: FATF    
Fat, Feces

Useful For Suggests clinical disorders or settings where the test may be helpful

Diagnosing fat malabsorption due to pancreatic or intestinal disorders


Monitoring effectiveness of enzyme supplementation in certain malabsorption disorders


This test is not useful for differentiating among pancreatic diseases.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Total fecal lipids include glycerides, phospholipids, glycolipids, soaps, sterols, cholesteryl esters, and sphingolipids. Excess fecal fat in feces, (steatorrhea) is indicative of malabsorption disorders, such as pancreatic insufficiency or Whipple disease. Therefore, measurement of the fecal fats can be useful in establishing a diagnosis of such pancreatic diseases as cystic fibrosis, chronic pancreatitis, neoplasia, or stone obstruction, and such intestinal diseases as Whipple disease, regional enteritis, tuberculous enteritis, gluten-induced enteropathy (also called celiac disease or sprue), and the atrophy of malnutrition.


Distinguishing free fatty acids from neutral fats, once thought to be helpful in the differential diagnosis of pancreatic disease, has fallen out of favor. Note that the composition of fats in the feces, normally predominately free fatty acids, can change significantly to predominately neutral fatty acids when the patient is on orlistat. This test does not distinguish between free and neutral fatty acids.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


> or =18 years: 2-7 g fat/24 hours

Reference values have not been established for patients who are <18 years of age.



All ages: 0-19% fat

Interpretation Provides information to assist in interpretation of the test results

Excretion of more than 7 grams fat/24 hours, when on a diet of 100 to 150 g of fat, is suggestive of a malabsorption defect.


Abnormal results from a random specimen should be confirmed by submission of a timed collection.


Test values for timed fecal fat collections will be reported in terms of g/24 hours; the duration of the collection may be 24, 48, 72, or 96 hours. Test values for random fecal fat collections will be reported in terms of percent fat.


Coefficient of Fat Absorption (CFA) can be calculated as follows:

            (grams fat consumed – grams of fat excreted) x 100

   CFA = --------------------------------------------------------------

                        grams of fat consumed

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Proper patient preparation is critical (see Specimen Required). Failure to adhere to a fat-controlled diet or to exclude other oils or oil substitutes from the diet may make interpretation difficult.


Barium interferes with test procedure; a waiting period of 48 hours before fecal collection is recommended.


The use of charcoal as a marker is not recommended. If charcoal is used, please notify the laboratory.

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Van de Kamer JH: Total Fatty Acids in Stool. In: Seligson D, ed. Standard Methods of Clinical Chemistry. Vol 2. Academic Press; 1958:34-38

2. Ellefson RD, Caraway WT: Lipids and Lipoproteins. In: Tietz NW, ed. Fundamentals of Clinical Chemistry. 2nd ed. WB Saunders Co; 1976:474-541

3. Shils ME, Ross AC, Caballero B, Cousins RJ, eds: Modern Nutrition in Health and Disease.10th ed. Lippincott Williams and Wilkins; 2006:1143-1151

4. Shils ME, Ross AC, Caballero B, Cousins RJ, eds: Modern Nutrition in Health and Disease.10th edition. Lippincott Williams and Wilkins; 2006:1227-1234

5. Hart PA, Conwell DL: Diagnosis of exocrine pancreatic insufficiency. Curr Treat Options Gastroenterol. 2015 Sep;13:347-353. doi:10.1007/s11938-015-0057-8