Testing Stool For the Cause of Diarrhea

Lab Tests to Diagnose the Cause of Diarrhea

Doctor looking at sample under microscope
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Unfortunately, diarrhea can be a very serious problem.   The combination of anesthesia, antibiotics, the dramatic change in diet and even medical problems can lead to an upset stomach that doesn't go away quickly or easily. 

For individuals who have diarrhea that doesn't clear up on its own, lab testing can help determine the cause of the problem.

What is Diarrhea?

Most people think of diarrhea as an episode of loose stool.

 Diarrhea is actually the term for four or more liquid stools per day.  Acute diarrhea is four or more liquid stools per day for less than fourteen days, while chronic diarrhea lasts longer than two weeks.  These liquid stools are often accompanied by stomach cramps and a general feeling of sickness.  

Why Diarrhea is Serious

Diarrhea is stool with excess water present.  The body is unable to process stool normally, removing the excess water in the intestine and producing a formed bowel movement.  Instead, excess water remains in the stool, and leaves the body as liquid.  This causes the body to lose electrolytes, vitamins, minerals and may cause dehydration. 

In countries where healthcare is difficult to find, diarrhea causes approximately five million deaths a year, mostly small children.  Even when healthcare is available, chronic diarrhea can be debilitating and require hospitalization to control.

Many individuals try to control the episodes by not eating or drinking, which can make the situation worse with dehydration and weakness.

Causes of Diarrhea

  • Change in diet
  • Bowel Preparation for surgery
  • Change in activity level
  • Thyroid 
  • Artificial sweeteners
  • Change in medications
  • Lactose intolerance
  • Antibiotic use
  • Inflamed bowel (Crohn's, ulcerative colitis)
  • Inability to absorb nutrients (celiac disease)
  • Clostridium Difficile

When to Seek Treatment for Diarrhea

Diarrhea can cause malnutrition, dehydration and pain if untreated.  Plan to seek treatment if your diarrhea lasts more than three days, if you feel weak or lightheaded, have blood in your stool or you develop a high fever (greater than 100.5)

Testing For Diarrhea

To test for potential causes of diarrhea, a stool sample must be collected.  A small amount of the stool should be collected in a sterile container to prevent contamination.  This can be done at your primary care provider's office, urgent care, or at an emergency room if the condition has become severe.

Stool Culture

This test examines stool for organisms that should not be present, or are present in too high of numbers.  The culture will determine what organisms are present and if they could potentially be causing the problem.

Clostridium Difficile Toxin

Clostridium difficile, or C. Diff, is a bacteria that causes chronic diarrhea.

 This bacteria, and others like it, may be present normally in the gut but begin to grow in numbers after treatment with an antibiotic.  This overgrowth can cause chronic diarrhea. 

Ova and Parasite

This test looks for signs of a parasite living in the intestinal tract. These parasites are more common in individuals who are from foreign countries without proper sanitation for food and water, individuals who travel to those areas, people who eat undercooked meat that is infected with parasites and people who swim or drink untreated water (such as while camping). 

This test looks at the stool sample under a microscope for pieces of a parasite or the eggs that they lay to reproduce.

Occult Stool

This test looks at the stool to see if there is blood present that cannot be seen with the naked eye.  It can also determine if the presence of a red color in the stool is caused by blood or by the presences of red food such as Jello or beets. 

Fecal Fat

This test looks at the fat level in stool.  Fat in the stool may indicate a problem with the intestines and the ability to absorb nutrients.

Stool Antigen

This test checks for antigens in the stool that may indicate the presence of giardiacryptosporidium and E. histolytica, parasites known for causing significant diarrhea.


Lab Tests Online. Diarrhea. Accessed November, 2015. https://labtestsonline.org/understanding/conditions/diarrhea/start/2/

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