Question: How do doctors find the cause of diarrhea?
Answer: If your doctor thinks it’s important to find the cause of your diarrhea, they may use your medical and family history, a physical exam, or tests.

Medical and family history

Your doctor may ask about your

symptoms, including how long you’ve had diarrhea, what yourstoollooks like, and how often you have diarrhea
eating and drinking habits
prescription and over-the-counter medicines
current and past medical conditions
recent international travel

Your doctor may also ask whether anyone in your family has digestive tract problems, food allergies and intolerances, or conditions that cause chronic diarrhea. Some conditions that cause chronic diarrhea, include

celiac disease
Crohn’s disease
diabetes
irritable bowel syndrome
lactose intolerance
ulcerative colitis

Physical exam

During a physical exam, your doctor may

check for signs of fever ordehydration
listen to sounds in yourabdomen, or belly, using a stethoscope
tap on your abdomen to check for tenderness or pain
perform adigital rectal exam
compare your current weight to past weights
Question: What tests do doctors use to diagnose diarrhea?
Answer: If your doctor decides diagnostic tests would be helpful, they may use one or more of the following tests to help find the cause of diarrhea.

Stool test

Doctors may use stool tests to check for blood, bacteria, parasites, or signs of diseases. 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

Blood tests can show signs of certain causes of diarrhea or problems such as dehydration. For a blood test, a health care professional will take a sample of your blood and send it to a lab. Doctors may use blood tests to check for certain diseases or disorders that can cause diarrhea.

Hydrogen breath test

A hydrogen breath test can be used to diagnose

lactose intolerance
dietary fructose intolerance
sucrose intolerance
small intestinal bacterial overgrowth

Normally, a small amount of hydrogen is found in your breath. If you have problems digesting carbohydrates like lactose, fructose, and sucrose, you may have high levels of hydrogen in your breath.

For this test, you will drink a liquid containing a specific carbohydrate. Over a few hours, you will breathe into a container that measures how much hydrogen is in your breath. During this time, a health care professional will ask you about your symptoms. If your hydrogen levels go up and your symptoms get worse during the test, your doctor may diagnose one of the above conditions.

Changes in diet

Your doctor may ask you to avoid foods with certain ingredients to see whether your diarrhea responds to a change in diet.

Endoscopy

Your doctor may use endoscopy to view the inside of your digestive tract and help find your cause of diarrhea. Endoscopy tests may include

colonoscopy
flexible sigmoidoscopy
upper gastrointestinal (GI) endoscopy