Fecal Fat Qualitative

The qualitative fecal fat test is a screening test for steatorrhea. Steatorrhea is the clinical syndrome caused by malabsorption of dietary fat. Causes of steatorrhea include Zollinger-Ellison syndrome, increased duodenal acid, abnormal bile output, pancreatic insufficiency, intestinal mucosal impairment, Whipple's disease, and various forms of enteritis, celiac disease, and sprue.  

Small fat droplets are observed in stools from healthy persons because there is always a small amount of fat from endogenous sources such as exfoliated epithelial cells. In patients with steatorrhea, the size and number of fat droplets are increased. The severity of steatorrhea can be graded only in broad terms because this is a qualitative test. Abnormal results should be confirmed with a timed-collection specimen and quantitative analysis.

False positive results may follow ingestion of nonabsorbable fat such as castor or mineral oil.  False negative results are associated with inadequate intake of dietary fat or dilution of intestinal contents with barium. 

Patient preparation is very important. For 3 days prior to and during the collection period, the patient should:

• Be on a fat controlled diet.
• Not consume any laxatives
• Avoid synthetic fat substitutes or fat blocking nutritional supplements. 

Barium interferes with the test procedure and a waiting period of 48 hours is recommended before stool collection. 

The percent of fat in a stool sample is determined by nuclear magnetic resonance spectrometer. Percent is then converted to grams of fat per 24 hours. 

Reference value for a randomly collected stool sample  is <20% fat

Reference value for a timed collection is 2-7 grams of fat per 24 hours.

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

Specimen requirement is 5 gm of frozen random stool collected in a container.

References

Go-Linn GW, Fordtran JS, Fecal fat concentration in patients with steatorrhea, Gastroenterology 1984;87(2):319-322.

Fine KD, Ogunji F, A New Method of Quantitative Fecal Fat Microscopy and Its Correlation With Chemically Measured Fecal Fat Output, Amer J Clin Pathol, 2000;113(4):528–534.

Korpi-Steiner NL, et al, Comparative analysis of fecal fat quantitation via nuclear magnetic resonance spectroscopy and gravimetry. Clin Chim Acta. 2009;400:33-36.