How to diagnose Diarrhea ?
If acute diarrhea lasts 2 days or less, diagnostic tests are usually not necessary. If diarrhea lasts longer or is accompanied by symptoms such as fever or bloody stools, a doctor may perform tests to determine the cause.
                
Diagnostic tests to find the cause of diarrhea may include the following:
                
- Medical history and physical examination. The doctor will ask about eating habits and medication use and will perform a physical examination to look for signs of illness.  - Stool culture. A sample of stool is analyzed in a laboratory to check for bacteria, parasites, or other signs of disease and infection.  - Blood tests. Blood tests can be helpful in ruling out certain diseases.  - Fasting tests. To find out if a food intolerance or allergy is causing the diarrhea, the doctor may ask a person to avoid foods with lactose, carbohydrates, wheat, or other ingredients to see whether the diarrhea responds to a change in diet.  - Sigmoidoscopy or colonoscopy. These tests may be used to look for signs of intestinal diseases that cause chronic diarrhea. For sigmoidoscopy, the doctor uses a thin, flexible, lighted tube with a lens on the end to look at the inside of the rectum and lower part of the colon. Colonoscopy is similar to sigmoidoscopy, but it allows the doctor to view the entire colon.