Diarrhea is diagnosed by the frequency and looseness of the stools. The cause of the diarrhea is diagnosed by considering other symptoms. These may include the presence of blood or mucus in the stool, the duration of the diarrhea, weight loss, or other signs of illness.
A healthcare provider will take a history of the infant's symptoms. He or she will then do a physical exam. The provider will look for signs of dehydration.
Labs tests, such as blood tests and tests on the stool, may be performed. Special X-rays may be taken, as well. Occasionally, an instrument known as a colonoscope is used to view the interior of the intestine. This can help determine the cause of the diarrhea.