Stool electron microscopy is an expensive diagnostic tool. It helps to identify the source of the antigen. The test helps to identify the various characteristics of the viral particle responsible for the infection. New viral strains are usually identified with the electron microscopic techniques. It is a time consuming process. A large number of stool samples are collected for the test.

Enzyme immunoassay test is usually superior to the conventional examination of stool samples with microscopes. Even small concentrations of viral antigens present in the stool sample can be identified with this diagnostic tool. The test is usually recommended when the physician suspects that the patient is suffering from a viral gastrointestinal infection. Noroviruses, rotaviruses, adenoviruses and astroviruses are usually detected through this test.

Stool culture is recommended for patients suffering from bloody diarrhea. The test is used to ascertain the exact cause of the infection. A positive stool culture indicates presence of bacteria in the stool sample, whereas a negative result is a sign of a non-bacterial infection. The stool sample collection procedure is same as that in the other stool tests. In the laboratory, the stool is exposed to conditions that facilitate bacterial and other organisms to grow. Through chemical tests and by looking at the appearance of the sample under a microscope, the organism present in the sample is identified. When a bacterium is found in the sample, a sensitivity test is done to select the best treatment option.

Stool microscopy is usually recommended for patients suffering from bloody diarrhea. To ensure that the stool sample is not contaminated with urine, the patient should urinate before the stool is collected. The sample should not be collected from the toilet bowl. Instead, it should be passed in a clean and dry container. In patients who have difficulty in passing the stool directly into the collection container owing to diarrhea, a large clean plastic bag is usually taped under the toilet seat for collecting the stool. The contents are then transferred to the collection container. The container should be promptly covered with a lid and sent to the laboratory as early as possible. Samples that are exposed to the air for a long time or analyzed after several hours might give inaccurate results. In stool microscopy, the stool is placed under a microscope. This test helps to detect bacterial infections in the gastrointestinal tract. Presence of white blood cells in the stool sample is a sign of infection caused by organisms that produce cytotoxin such as salmonella, yersinia enterocolitica or shihella.

A blood test helps to confirm an infection. A full blood count test provides information on different parameters of each blood cell. To get an accurate report of the blood test, a fresh blood sample should be analyzed. Elevated white blood cells and granulocyte count indicates an infection. However, in several cases of gastroenteritis, the full blood count test does not provide sufficient information to support early diagnosis of gastrointestinal infection.

The electrolyte, creatinine and urea levels are usually not required in cases of simple gastroenteritis. However, in cases of severe dehydration, assessing the electrolyte, creatinine and urea concentrations in the blood helps to detect complications that develop due to excessive water loss. Besides aiding diagnosis, these tests are needed for modifying the treatment for managing the fluid balance, acid-base balance and the functions of the kidneys and other vital organs of the body.

Through questionnaires a physician gathers the medical history of the patient. The health care practitioner usually asks questions about the frequency and duration of the bowel movement, features of the stool, incidence of vomiting and urination frequency. While diagnosing the ailment, the physician also takes into account the foods and medicines taken by the patient, the food preparation method, the storage procedure, exposure to toxic substances and travel history. Physical examinations are needed to ascertain whether any other health problems unrelated to the stomach infection is responsible for the symptoms. The physician checks for abnormalities in the abdomen and the anus.