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Inmedicine, thefecal fat test is a diagnostic test forfatmalabsorption conditions, which lead to excess fat in the feces (steatorrhea).
In theduodenum, dietary fat (primarilytriglycerides) is digested byenzymes such aspancreatic lipase into smaller molecules of 1,2-Diacylglycerols and free fatty acids, which can be absorbed through the wall of thejejenum of the small intestine[1] and entercirculation formetabolism and storage. Sincefat is a valuable nutrient,human feces normally contains very little undigested fat. However, a number of diseases of the pancreas and gastrointestinal tract are characterized by fat malabsorption.
Examples of such diseases are:
In the simplest form of the fecal fat test, a random fecal specimen is submitted to thehospital laboratory and examined under amicroscope afterstaining with aSudan III orSudan IV dye ("Sudan staining"). Visible amounts of fat indicate some degree of fat malabsorption.
Quantitative fecal fat tests measure and report an amount of fat. This is usually done over a period of three days, the patient collecting all of their feces into a container.
The container is thoroughly mixed to homogenize the feces, without using specific mixer equipment. A small sample from the feces is collected. The fat content is extracted withsolvents and measured bysaponification (turning the fat intosoap).
Normally, up to 7grams of fat can be malabsorbed in people consuming 100 grams of fat per day. In patients withdiarrhea, up to 12 grams of fat may be malabsorbed since the presence of diarrhea interferes with fat absorption, even when the diarrhea is not due to fat malabsorption.