The evaluation of diarrhea begins with a medical history and physical examination.

Physical findings in someone with diarrhea may include:

• Fever
• Signs of dehydration

Signs of dehydration:

• Pale, dry skin
• Dry eyes and mouth
• Sunken eyes
• Sunken fontanelle in infants
• Rapid pulse
• Low blood pressure when standing
• Confusion
• Lethargy:
• A condition of excessive sleepiness or drowsiness.
• Decreased urination
• Urinating less than 3 times over 24 hours

Most cases of diarrhea do not require testing. Tests may be required to evaluate diarrhea that is prolonged, or diarrhea that contains blood or pus.

The diagnosis of an infectious cause for diarrhea must be confirmed through testing. A stool culture is performed on a stool specimen, in order to investigate suspected bacterial infection. Stool may also be tested for C. difficile toxin, which is used to diagnose pseudomembranous colitis. A stool examination for ova and parasites may be helpful to detect parasitic infections.

A stool culture can detect:

• Cholera
• Shigella infection
• Campylobacter enteritis
• Cryptosporidium enterocolitis
• Giardiasis
• Pseudomembranous colitis:
• Clostridium difficile
• Salmonella gastroenteritis
• Traveler's diarrhea due to bacterial infection
• E. coli

Tests that may be used to evaluate diarrhea include:

• Complete blood count
• Liver profile
• Kidney profile
• CT scanning of the abdomen:
• Urinalysis