Diagnosis

Despite clinical clues, determining the causative agent of diarrhea in an individual patient on the basis of clinical grounds alone is usually difficult. Stool cultures are usually unnecessary for immuno-competent patients who present within 24 hours after the onset of acute, watery diarrhea. Microbiologic investigation is indicated in patients who are dehydrated or febrile or have blood or pus in their stool. Epidemiologic clues to infectious can be found by evaluating the incubation period, history of recent travel, unusual food or eating circumstances, professional risks, and recent use of antimicrobials, institutionalization, and HIV infection risks.
A stool sample may help define the type of diarrhea. The presence of fat, occult blood, and white blood cells will help determine if a watery, inflammatory, or fatty diarrhea is present. A bacterial culture and ova/parasite studies of a stool specimen will also help determine if an infectious etiology is present. Other investigations include: a blood count to look for anemia and infections, an electrolyte and kidney function panel to assess for electrolyte abnormalities and renal insufficiency, and albumin to assess nutritional status.