Fecal fat test

The fecal fat test is a diagnostic test for fat malabsorption conditions, which lead to excess fat in the feces, known as steatorrhea.

In the duodenum, dietary fat primarily as triglycerides is digested by enzymes such as pancreatic lipase into smaller molecules of 1,2-Diacylglycerols and free fatty acids, which can be absorbed through the wall of the jejenum of the small intestine and enter circulation for metabolism and storage. 

Feces normally contains very little undigested fat. 

Diseases of the pancreas and gastrointestinal tract are characterized by fat malabsorption:

disorders of exocrine pancreatic function, such as chronic pancreatitis, cystic fibrosis and Shwachman–Diamond syndrome: characterized by deficiency of pancreatic digestive enzymes.

celiac disease 

short bowel syndrome

small bowel bacterial overgrowth syndrome

The  fecal fat test, a random fecal specimen is examined under a microscope after staining with a Sudan III or Sudan IV dye.

Visible amounts of fat indicate some degree of fat malabsorption.

Quantitative fecal fat tests measure an amount of fat, usually done over a period of three days, the patient collecting all of their feces into a container.

The fat content is extracted with solvents and measured by saponification.

In  people consuming 100 grams of fat per day, up to 7 grams of fat can be malabsorbed.

The test includes 100 g of fat in the diet for two days before and throughout the stool collection period

A normal value for the coefficient of fat absorption is at least 93%, and a normal amount of fat in stool  is less than 7 g for 24 hours with elevated values occurring in disorders absorption and digestion

Challenges to routine testing late to patient adherence to the recommended diet, complete stool collections, and cumbersome manual laboratory testing and analysis.

With diarrhea, up to 12 grams of fat may be malabsorbed: the presence of diarrhea interferes with fat absorption, even when the diarrhea is not due to fat malabsorption.

A fecal fat test should be performed to confirm pancreatic insufficiency if fecal elastase levels or vitamin A or E levels are very low in the absence of classic symptoms of steatorrhea.

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