Stool tests
There are many stool tests; they are laboratory tests used to detect infections and diseases that may affect the intestine, liver and pancreas. Stool tests include:
- Examination of shape and consistency, chemical, physical and microscopic examination
- Tests for parasites
- Tests for bacteria (stool culture)
- Faecal occult blood test
Why they are done
Stool tests are generally recommended by the family doctor or a gastroenterologist when there is diarrhoea, constipation, bloating (wind) or abdominal pain, to diagnose the cause of these troublesome symptoms (for example bacteria, parasites, fungi, etc.). Depending on the person’s state of health, the doctor recommends the most suitable stool test in each case (for example, for someone over 45 they may recommend a faecal occult blood test, for a child a stool culture to check for infection, and so on).
How it is done
A stool sample about the size of a hazelnut is collected in a sterile container with the help of a spatula or small spoon. The sample must not be contaminated with urine, otherwise the result may be distorted by substances in the urine. Disposable containers should be used, which can be bought at a pharmacy or are provided by the laboratory that will analyse the sample. If the stool is being tested for occult blood, avoid collecting the sample during your period, and if it is being tested for bacteria, tell your doctor if you are taking antibiotics, as these can affect the test, i.e. bacteria may appear to be absent when in fact they are present.
Results
Examination of the shape and consistency of stools, and chemical, physical and microscopic examination: normal stools are soft, pasty and cylindrical. They are brown because of stercobilinogen (a breakdown product of bilirubin), but paler if the diet is rich in vegetables and fruit; they are golden yellow in newborn babies and black if you eat blueberries or take iron (they can also be black when there is bleeding in the intestine).
If stools are abundant, soft and shapeless, the cause may be a diet rich in vegetables.
If stools are scanty, hard and well formed, the cause may be a diet too rich in proteins and carbohydrates.
If food components are present that should be absent, intestinal transit is accelerated and these substances are not being properly absorbed, for example because of liver or pancreatic problems.
Tests for parasites: parasites should be absent from stools.
• If, however, they are present, the report gives the name of the parasite identified so that the doctor can recommend the best treatment to eliminate it. Tests for bacteria (stool culture): “pathogenic” bacteria, i.e. those that cause infection, should be absent from stools. • If, however, they are present, the report gives the name of the pathogenic bacterium identified, and the laboratory automatically carries out an antibiogram, a test in which the bacterium is identified, isolated and exposed to antibiotics in order to find the most suitable treatment for that specific type of infection. Faecal occult blood test: blood should be absent from stools. If, however, it is present, even in very small amounts, the cause is a lesion in the intestine that should be investigated further with more specific tests, such as colonoscopy.