Fecal fat
Encyclopedia
In medicine
, the fecal fat test is a diagnostic test for fat
malabsorption
conditions, which lead to excess fat in the feces (steatorrhea
).
, dietary fat (primarily triglyceride
s) is digested by enzyme
s 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.
Examples of such diseases are:
after staining with a Sudan III
or Sudan IV
dye ("Sudan stain
ing"). Visible amounts of fat indicate some degree of fat malabsorption.
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 solvent
s and measured by saponification
(turning the fat into soap
).
Normally up to 7 gram
s 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 malabsorption.
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, the fecal fat test is a diagnostic test for fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
malabsorption
Malabsorption
Malabsorption is a state arising from abnormality in absorption of food nutrients across the gastrointestinal tract.Impairment can be of single or multiple nutrients depending on the abnormality...
conditions, which lead to excess fat in the feces (steatorrhea
Steatorrhea
Steatorrhea is the presence of excess fat in feces. Stools may also float due to excess lipid, have an oily appearance and be especially foul-smelling. An oily anal leakage or some level of fecal incontinence may occur. There is increased fat excretion, which can be measured by determining the...
).
Background
In the small intestineSmall intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
, dietary fat (primarily triglyceride
Triglyceride
A triglyceride is an ester derived from glycerol and three fatty acids. There are many triglycerides, depending on the oil source, some are highly unsaturated, some less so....
s) is digested by enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s such as pancreatic lipase
Pancreatic lipase
Pancreatic lipase, also known as pancreatic triacylglycerol lipase, is secreted from the pancreas, and is the primary lipase that hydrolyzes dietary fat molecules in the human digestive system, converting triglyceride substrates found in ingested oils to monoglycerides and free fatty acids.Bile...
into smaller molecules which can be absorbed through the wall of the small intestine and enter the circulation for metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
and storage. As fat
Fat
Fats consist of a wide group of compounds that are generally soluble in organic solvents and generally insoluble in water. Chemically, fats are triglycerides, triesters of glycerol and any of several fatty acids. Fats may be either solid or liquid at room temperature, depending on their structure...
is a valuable nutrient, human feces
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
normally contain 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:
- disorders of exocrine pancreaticPancreasThe pancreas is a gland organ in the digestive and endocrine system of vertebrates. It is both an endocrine gland producing several important hormones, including insulin, glucagon, and somatostatin, as well as a digestive organ, secreting pancreatic juice containing digestive enzymes that assist...
function, such as chronic pancreatitisChronic pancreatitisChronic pancreatitis is a long-standing inflammation of the pancreas that alters its normal structure and functions. It can present as episodes of acute inflammation in a previously injured pancreas, or as chronic damage with persistent pain or malabsorption....
, cystic fibrosisCystic fibrosisCystic fibrosis is a recessive genetic disease affecting most critically the lungs, and also the pancreas, liver, and intestine...
and Shwachman-Diamond syndrome (these are characterized by deficiency of pancreatic digestive enzymes) - celiac disease (in which the fat malabsorption in severe cases is due to inflammatory damage to the integrity of the intestinal lining)
- short bowel syndromeShort bowel syndromeShort bowel syndrome is a malabsorption disorder caused by the surgical removal of the small intestine, or rarely due to the complete dysfunction of a large segment of bowel. Most cases are acquired, although some children are born with a congenital short bowel...
(in which much of the small intestine has had to be surgically removed and the remaining portion cannot completely absorb all of the fat). - small bowel bacterial overgrowth syndromeSmall bowel bacterial overgrowth syndromeSmall bowel bacterial overgrowth syndrome , or small intestinal bacterial overgrowth , also termed bacterial overgrowth; is a disorder of excessive bacterial growth in the small intestine. Unlike the colon , which is rich with bacteria, the small bowel usually has less than 104 organisms per...
Microscopy
In the simplest form of the fecal fat test, a random fecal specimen is submitted to the hospital laboratory and examined under a microscopeMicroscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
after staining with a Sudan III
Sudan III
Sudan III is a lysochrome diazo dye used for staining of triglycerides in frozen sections, and some protein bound lipids and lipoproteins on paraffin sections. It has the appearance of reddish brown crystals and a maximum absorption at 507 nm.Sudan III is a dye used for Sudan staining...
or Sudan IV
Sudan IV
Sudan IV is a lysochrome diazo dye used for the staining of lipids, triglycerides and lipoproteins on frozen paraffin sections. It has the appearance of reddish brown crystals with melting point 199 °C and maximum absorption at 520 nm.Sudan IV is one of the dyes used for Sudan staining. Similar...
dye ("Sudan stain
Sudan stain
Sudan staining is the use of Sudan dyes to stain sudanophilic substances, usually lipids. Sudan lysochromes are used....
ing"). 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.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 solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
s and measured by saponification
Saponification
Saponification is a process that produces soap, usually from fats and lye. In technical terms, saponification involves base hydrolysis of triglycerides, which are esters of fatty acids, to form the sodium salt of a carboxylate. In addition to soap, such traditional saponification processes...
(turning the fat into soap
Soap
In chemistry, soap is a salt of a fatty acid.IUPAC. "" Compendium of Chemical Terminology, 2nd ed. . Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford . XML on-line corrected version: created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN...
).
Normally up to 7 gram
Gram
The gram is a metric system unit of mass....
s of fat can be malabsorbed in people consuming 100 grams of fat per day. In patients with diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
, 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.