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 stool, (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 stool, 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.
Diagnosing fat malabsorption due to pancreatic or intestinal disorders
Monitoring effectiveness of enzyme supplementation in certain malabsorption disorders
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
This test is not useful for differentiating among pancreatic diseases.
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 stool collection analysis is recommended.
The use of diaper rash ointments will falsely elevate test results. Discontinue use during collection period.
The use of charcoal as a marker is not recommended. If charcoal is used, please notify the laboratory.
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
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Van de Kamer JH: Total Fatty Acids in Stool. In Standard Methods of Clinical Chemistry. Vol 2. Edited by D Seligson. Academic Press, New York, 1958, pp 34-38
2. Ellefson RD, Caraway WT: Lipids and Lipoproteins. In Fundamentals of Clinical Chemistry. Second Edition. Edited by NW Tietz. Philadelphia, WB Saunders Co, 1976, pp 474-541
3. Shils ME, Ross AC, Caballero B, Cousins RJ: Chapter 71, pp 1143-1151 and Chapter 78, pp 1227-1234: In Modern Nutrition in Health and Disease.10th edition. Baltimore, MD, Lippincott Williams and Wilkins, 2006