Stool test, what is it used for

Stool test, what is it used for

What is a stool test?

It is a diagnostic test that is used in medicine for the study of digestive system´s alterations mainly. It consists of collecting a small quantity of stool for after be analyzed in the laboratory. Usually it is indicated for:

Physical study: it values the consistency, density, color and smell of the stool.

Biochemical study: the components that form the stool are studied. You must take into account that in normal conditions the stool are a 70% of water, and the 30% remaining is represented by others components as fats, proteins, bacteria and fibers, that cannot be digested.

Van Kamer´s test: it is a specific test for measure the quantity of fats in the stool with more accuracy than a biochemical study. Several samples are needed.

Detection of enzymes: mainly the presence of pancreatic enzymes in the stool is studied, which ones are essential for digestion.

Hidden blood in stool: it allows to detect the presence of small quantity of blood mixed with the stool. Now a days, it is recommend to people older than 50 years of age realize this test annually as a help in the detection of colon cancer (though for early diagnosis of this kind of cancer the more effective test is the colonoscopy), and it also can be useful for detect unknown tumors. In some countries reactive strips of paper are sold at the drug stores.

Fresh examination: it consists of diluting the stool and observe them directly under the microscope. It allows to detect parasites and its eggs, and others bigger elements.

Stool culture: at the same way that blood elements can be isolated through a blood culture, or the urine with a urine culture, with the stool it can be realized a stool culture for isolate pathogen germs.

When is a stool test done?

The stool test is an exam which is made frequently in medicine because it does not involve great discomfort, it is cheap and it can provide a lot of useful information. However, this information is limited to the digestive tube and associated glands mainly, because of that it is just request when alterations in these levels are suspected and they can be studied through blood tests or urine tests, which are more comfortable to pick up.

The disease where a stool test is more requested are: 

Inflammatory bowel disease: Ulcerative Colitis or disease of Crohn.

Intestinal Malabsorption: from a Celiac disease to a Whipple´s disease. There are tens of other causes.

Pancreatic insufficiency: when the pancreas does not segregate the necessary enzymes for the digestion.

Digestive tract cancer: it can guide us to that diagnosis, though it is usually a phase too late.

Infections: as Salmonellosis, Giardiasis, Amebiasis, among others.

Preparation for the stool test

Issues that you must have into account: 

Duration: it takes a very short time. The pickup of the sample of stool you can do it at home. The stool can be picked up at any hour, and it must be avoided that the stool get mixed with urine. After, you should just deliver it at  doctor´s consultation in less than 24 hours.

Hospital admission: it never requires hospital admission. It is a test that can be done on an outpatient basis.

Is company needed? : No

Medicines: it is not necessary to take any previous medicine. You have tell to the doctor all the medications that you have being taking, because some medicines can change the normal characteristics of stool. Many of them are easy to relate (laxatives, as example), but other can go unnoticed (such as, herbalist and slimming products).

Clothes: You do not need special clothes for pick up or deliver the sample.

Documentation: it is recommended to bring your health card and the test sheet when you will deliver the sample.

Pregnancy and lactation: The test can be done without modify any activity, though it is better if the doctor knows that you are pregnant, because the stool can be slightly different. 

Contraindications: they do not exist. It is recommended not do the pickup of the sample when you have the menstruation.

How is a stool test done?

Before request you a stool test, when you arrive at the consultation the doctor will ask you some general questions about your health condition: important diseases, risk factors, life style, place of work and, above all, he will insist about the gastrointestinal symptoms that you had appreciated. He will ask you about the quantity of daily bowel movements, its consistency and color.

Other questions that he can do to you are if you have had fever or if you have lost a lot of weight in the last months. After he will realized a general physical exploration, and he will value the realization of stool test. He will give you a sheet in the one he solicits the test and where he will point the data that he wants for be analyzed at the laboratory.   

Days after this first visit, or at the same moment, you will be able to pick up the sample and take it to the clinic. You will need a sterile bottle that they will give to you at the doctor´s consultation or you must have to buy it at the drug store. 

When you will pick up the sample it is recommended have your anus and perineum clean for avoid contamination, and it is better if you do not touch the bottle´s edges, and trait to avoid that they have contact with anything. The sample collected must have the size of a chestnut if it is solid stool, or a 10mL if it is liquid. If the sample is bigger than this, the gases that the bacteria produce can press the bottle and break it. 

When you finish to pick up the sample, close the bottle carefully but with firmness for it stays airtight. Left the bottle inside the refrigerator and deliver it to the clinic in the next 24 hours. If you left the bottle during many hours at home it can be contaminated with microbes or lose useful substances for the test. When you arrive at the consultation you just have to deliver it and you can go. The results may take from hours to days, and they will give them to you at the doctor´s consultation.     

Stool test´s complications

There not exist any complications with the stool test.

The results of the stool test can include:


Alterations can be detected in the percentage of the stool components. The percentages are not exact and they vary easily in every sample.

Proteins: 2-3%. The biggest presence of proteins in the stool can be related with the diet or with the wrong digestion of proteins. It is related with the constipation. 

Fats: 10-20%. When the percentage of fats exceed the 20% we can speak of the steatorrhea. It is because a wrong digestion or a malabsorption of the fats in the digestive tube. It is related with the diarrhea.

Minerals: 10-20%. They do not have a big importance in the stool´s study. The malabsorption of themselves are better study in a blood test.

Indigestible remains (fiber): 30%. They depend directly of the diet, they do not have importance in any disease.

Bacteria: 30%. The percentage is usually very stable. The characteristics of these microorganisms are the most important and they are study with a stool culture.

Detection of enzymes

The enzymes that act in the digestive tube are secreted by the stomach and the pancreas mainly. There are also others who act in the gut wall, but they are fixed and they cannot be studied in a stool test.

The most important are: 

Peptidase: secreted by the stomach, it digests peptides. Not usually studied in stool.

Lipase: secreted by the pancreas, it digests lipids.

Tryptase: secreted by the pancreas, it digests some proteins.

Elastase: secreted by the pancreas, too, it digests elastic proteins.

The study of these enzymes consist simply in detect their presence or not. When they are not it can be because an exocrine pancreatic insufficiency (that it is related with chronic pancreatitis) or an obstruction in the lower bile duct (by bile lithiasis, as example).

Fresh examination

With the directly visualization of the dissolved stool with serum we can separate the biggest elements of the stool and watch the following structure: 

Fibers: they are the most seeing, their presence is normal.

Parasites: it is easy to observe amoebas or giardia when they are invading the digestive tube. 

Cysts: usually both amoebas and giardia are observed in cysts form in this exam. So they can resist passage through the anus.

Eggs: some parasites are very big so they can go out of the anus, but their eggs do it. This is the case of intestinal worms as Stronyliodes, Azcaris, etc.  

Stool culture 

It can be studied the different strain of bacteria that are in the stool. The usual is find commensal bacteria of the large intestine, but in situations of infection they are observed aggressive pathogens such as Salmonella or Shigella.