Gastroenteritis may be diagnosed by a physician during a physical examination that includes a medical history and list of medications. Patients are typically asked to describe the type and duration of symptoms experienced, such as diarrhea, nausea, vomiting and/or abdominal cramping. However, many people (particularly adults) do not consult a physician for mild cases of gastroenteritis.

Other information that patients may be asked to provide includes:

• Foods consumed in the past few days
  
  
• Recent travel, especially to foreign countries (which can result in a condition known as traveler’s diarrhea)
  
  
• Changes in medications
  
  
• Friends and/or family members who are experiencing similar symptoms

Physicians may examine the abdomen for the presence of tenderness or masses, which sometimes indicate the presence of another underlying condition, such as appendicitis (inflammation of the appendix) or cholecystitis (inflammation of the gallbladder).

There is no specific test to diagnose gastroenteritis. If patients have been experiencing symptoms for 48 hours or longer, physicians may request a stool sample, which will be examined in a laboratory under a microscope after being put in a culture medium to detect the presence of bacteria, parasites or other microorganisms that may be causing the illness. Gastroenteritis caused by a rotavirus infection can be diagnosed with a stool test. Most cases of viral gastroenteritis are not diagnosed because symptoms are usually mild and are not seen by a physician.

If symptoms last for longer than a few days, a physician may perform a colonoscopy (an examination of the inside of the colon). This test will help determine whether a condition other than gastroenteritis, such as ulcerative colitis  (chronic inflammation of the colon that produces ulcers in its lining), is causing symptoms.