In medicine, a fecal fat test is a diagnostic test for fat malabsorption conditions (also referred to as steatorrhea).
Background
In the small intestine, dietary fat (primarily triglycerides) is digested by enzymes such as pancreatic lipase into smaller molecules which can be absorbed through the wall of the small intestine and enter the circulation for metabolism and storage. As fat is a valuable nutrient, human feces normally contain very little undigested fat. However, a number of diseases of the pancreas and gastrointestinal tract are characterized by fat malabsorption.
celiac disease (in which the fat malabsorption in severe cases due to inflammatory damage to the integrity of the intestinal lining)
short gut syndrome (in which much of the small intestine has had to be surgically removed and the remaining portion cannot completely absorb all of the fat).
Microscopy
In the simplest form of the fecal fat test, a random fecal specimen is submitted to the hospital laboratory and examined under a microscope after staining with a dye called Sudan IV. Visible amounts of fat indicate some degree of fat malabsorption.
Quantitative fecal fat test
Quantitative fecal fat tests measure and report an amount of fat. This usually done over a period of three days, the patient collecting all of their feces into a container. This is generally an unpleasant experience for both patient and staff.
The container is thoroughly mixed to homogenize the feces, this can be done with a paint mixer. A small sample from the feces is collected. The fat content is extracted with solvents and measured by saponification (turning the fat into soap).
Normally up to 7 grams of fat can be malabsorbed in people consuming 100 grams of fat per day. In patients with diarrhea, 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 malabsorbtion.
The fecalfat test measures the amount of fat in the stool, and the percentage of dietary fat that is not taken in by the body.
This test is used to evaluate fat absorption as an indication of how the liver, gallbladder, pancreas, and intestines work.
Normal fat absorption requires bile from the gallbladder (or liver if the gallbladder has been removed), enzymes from the pancreas, and normal intestines.
Stool fats, also known as fecalfats, or fecal lipids, are fats that are excreted in the feces.
Therefore, a fat retention coefficient is determined by measuring the difference between ingested fat and fecalfat, and expressing that difference as a percentage.
Increased fecalfat levels are found in cystic fibrosis, malabsorption secondary to other conditions like Whipple's disease or Crohn's disease, maldigestion secondary to pancreatic or bile duct obstruction, and "short-gut" syndrome secondary to surgical resection, bypass, or congenital anomaly.
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