There are several different types of fecal tests. A general stool culture is used to look for the presence of bacteria or parasites that may have infected the patient's intestine. In most cases, a single sample will be enough to reveal bacteria or parasites, but in some cases samples from up to three different bowel movements will be necessary.

Patients may also be given a fecal occult blood test (FOBT), which uses a chemical process to detect hidden blood (occult) in a person’s stool. The presence of such blood may result from inflammatory disorders, infections, vascular problems or tumors. Use of certain medications – including nonsteroidal anti-inflammatory drugs, antibiotics and anticoagulants – can also cause this type of bleeding.

The most commonly used fecal occult blood test is the guaiac-based Hemoccult II. Guaiac is a colorless chemical compound that turns blue when it is exposed to blood. Guaiac-based tests are easy to use and can be performed anywhere.

New tests have been developed as scientists try to improve the accuracy of fecal occult blood tests. The HemeSelect and HemoQuant tests measure fecal hemoglobin (iron-containing pigment in red blood cells), and thus do not require the pre-test dietary restrictions of other tests. However, they must be performed in a laboratory setting and are no more accurate than a Hemoccult II test. These tests may be use to screen for colorectal cancer. The value of all of these tests should be clarified once the results of ongoing studies are known.

Although an FOBT can reveal the presence of blood, it does not indicate the source of the bleeding. Further tests are necessary to track down the underlying illness, and may include evaluation of the colon, rectum and upper intestinal tract (which includes the esophagus, stomach and small bowel).

Other common fecal tests include:

• Fecal immunochemical test (FIT). A newer kind of stool blood test kit that detects a specific portion of a human blood protein. The test is performed in the same manner as an FOBT, but the fact that it is more specific reduces the number of false positives. Some patients may find this easier to use than the traditional FOBT, as only two samples are necessary and vitamins and foods do not affect the test.
  
  
• Fecal fat test. Measures the body's ability to break down and absorb fat. Normally, fat is completely absorbed from the small intestine and into the body. Therefore, the stool contains little or no fat. However, certain digestive disorders may cause some fat to be incompletely absorbed, which results in fat in the stool. The inability to absorb fat is called steatorrhea. Fecal fat tests can be used to detect possible disorders of the liver, gallbladder, pancreas or intestines. These tests are not routinely available at most medical centers.
  
  

  

• Stool weight test. This test helps determine which part of the intestine is affected and helps the physician narrow down possible causes of diarrhea. Heavier stools may indicate higher water content, which may be a result of dehydration.
  
  
• Stool electrolyte test. Helps differentiate among the different types of watery diarrhea.
  
  
• Stool pH test. Low pH readings may indicate malabsorption of sugars and starches.
  
  
• Stool white blood cell test. High numbers of white blood cells may indicate that an inflammatory condition is causing a person’s diarrhea.
  
  
• Stool magnesium test. High magnesium levels may indicate excessive dietary magnesium from supplements, antacids or laxatives.
  
  
• Stool pancreatic enzyme test. Test used to examine levels of two pancreatic enzymes – chymotrypsin and elastase – in a stool sample. High levels may indicate a pancreatic condition.
  
  
• Stool tests for laxatives. Though routine stool tests can reveal the presence of laxatives, this test can help pinpoint the specific laxative responsible for symptoms such as diarrhea.
  
  
• Fecal DNA test. DNA from colorectal neoplasms (abnormal growths) is shed in the stool where it can be isolated and tested for the presence of changes acquired during the development of cancer. An entire bowel movement must be collected for DNA testing, and specimens must be shipped with an ice pack. Many patients are likely to find the process more complex or bothersome than FOBT.