Diagnosis of Diarrhea


How do doctors find the cause of diarrhea?

Doctors do not typically need to find a cause of acute diarrhea. If your diarrhea lasts longer than 4 days or you have symptoms such as fever or bloody stools, your doctor may need to find the cause. Your doctor may use information from your medical and family history, a physical exam, or tests to find the cause of your diarrhea.

Medical and family history

Your doctor will ask for information about your symptoms, such as

  • how long you have had diarrhea
  • how much stool you have passed
  • how often you have diarrhea
  • how your stool looks, such as color or consistency
  • whether you have other symptoms along with diarrhea

Your doctor will ask about the foods you eat and the beverages you drink. If your doctor suspects you have a food allergy or intolerance, he or she may recommend that you change what you eat to see if your symptoms improve.

Your doctor will also ask about

  • current and past medical conditions
  • prescription and over-the-counter medicines
  • recent contact with other people who are sick
  • recent travel to developing countries

Your doctor may ask whether anyone in your family has a history of conditions that cause chronic diarrhea, such as celiac disease, Crohn’s disease, irritable bowel syndrome, lactose intolerance, and ulcerative colitis.

Physical exam

During a physical exam, your doctor may

Sometimes, doctors perform a digital rectal exam. Your doctor will have you bend over a table or lie on your side while holding your knees close to your chest. After putting on a glove, the doctor will slide a lubricated finger into your anus to check for blood in your stool.

Source: NIDDK (NIH)1

   •   •   •

Back to: « Diarrhea

   •   •   •

The exact cause of diarrhoea can only be diagnosed by laboratory tests of faecal specimens. Sometimes several specimens must be tested.

Source: Queensland Health2

Tests for Diarrhea

What tests do doctors use to find the cause of diarrhea?

Your doctor may use the following tests to help find the cause of your diarrhea.

Stool test

Stool tests can show the presence of blood, bacteria, or parasites; or signs of diseases and disorders. A health care professional will give you a container for catching and storing the stool. You will receive instructions on where to send or take the container for analysis.

Blood tests

A health care professional may take a blood sample to test for certain diseases or disorders that can cause diarrhea.

Hydrogen breath test

This test is used to diagnose lactose intolerance by measuring the amount of hydrogen in your breath. Normally, little hydrogen is detectable in your breath. With lactose intolerance, undigested lactose produces high levels of hydrogen in your breath. For this test, you will drink a beverage that contains a known amount of lactose. You will then breathe into a balloon-type container that measures your breath hydrogen level. If the hydrogen level is high, your doctor will diagnose lactose intolerance.

Fasting tests

To find out if a food intolerance or allergy is causing your diarrhea, your doctor may ask you to avoid foods with lactose, carbohydrates, wheat, or other ingredients to see whether your diarrhea responds to a change in diet.


Your doctor may use endoscopy to look inside your body to help find the cause of your diarrhea. Endoscopic procedures include

Source: NIDDK (NIH)3

Differential Diagnosis for Diarrhea

Four types of viruses cause most cases of viral gastroenteritis.

Some forms of gastroenteritis are caused by bacteria [bacterial gastroenteritis] or parasites [parasitic gastroenteritis] rather than viruses.

Source: NIDDK (NIH)4

   •   •   •


  1. Source: NIDDK (NIH): niddk.nih.gov/ health-information/ digestive-diseases/ diarrhea/ all-content
  2. Source: Queensland Health: conditions.health.qld.gov.au/ HealthCondition/ condition/ 14/ 33/ 39/ diarrhoea-in-young-children
  3. Source: NIDDK (NIH): niddk.nih.gov/ health-information/ digestive-diseases/ diarrhea/ all-content
  4. Source: NIDDK (NIH): niddk.nih.gov/ health-information/ digestive-diseases/ viral-gastroenteritis

   •   •   •

Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.