Acute diarrhea. Acute diarrhea usually requires few tests.

• Measurement of blood pressure in the upright and supine (lying) positions can demonstrate orthostatic hypotension and confirm the presence of dehydration. If moderate or severe dehydration or electrolyte deficiencies are likely, blood electrolytes can be measured.
• Examination of a small amount of stool under the microscope may reveal white blood cells indicating that intestinal inflammation is present and prompting further testing, particularly bacterial cultures of stool and examination of stool for parasites.
• If antibiotics have been taken within the previous two weeks, stool should be tested for the toxin of C. difficile.
• Testing stool or blood for viruses is performed only rarely, since there is no specific treatment for the viruses that cause gastroenteritis.
• If there has been recent travel to undeveloped countries or the mountains, stool may be examined under the microscope for Giardia and other parasites.
• There are also immunologic tests that can be done on samples of stool to diagnose infection with Giardia.

Chronic diarrhea. With chronic diarrhea, the focus usually shifts from dehydration and infection (with the exception of Giardia, which occasionally causes chronic infections) to the diagnosis of non-infectious causes of diarrhea.

• This may require X-rays of the intestines (upper gastrointestinal series or barium enema), or endoscopy (esophagogastroduodenoscopy or EGD, or colonoscopy) with biopsies.
• Fat malabsorption can be diagnosed by measuring the fat in a 72-hour collection of stool.
• Sugar malabsorption can be diagnosed by eliminating the offending sugar from the diet or by performing a hydrogen breath test. Hydrogen breath testing also can be used to diagnose bacterial overgrowth of the small intestine.
• An underactive pituitary or adrenal gland and an overactive thyroid gland can be diagnosed by measuring blood levels of cortisol and thyroid hormone, respectively.
• Celiac disease can be diagnosed with blood tests and a biopsy of the small intestine.

This answer should not be considered medical advice...This answer should not be considered medical advice and should not take the place of a doctor’s visit. Please see the bottom of the page for more information or visit our Terms and Conditions.