Diarrhoea is diagnosed clinically and the doctor usually does not recommend any tests for acute diarrhoea. Most cases of acute diarrhoea in adults and children settle within a week and you may not even need to visit a doctor.
Medical history and physical examination: To diagnose the cause of your diarrhoea, your doctor may ask questions such as:
The doctor will examine to look for signs of dehydration such as low blood pressure, poor or weak peripheral pulses, skin turgor (skin elasticity decrease that is the skin does not flatten back to normal right away after being gently pinched and released). In infants the doctor will examine the soft spot on the head (fontanelle) to look for dehydration (it becomes sunken if the infant is dehydrated).
Stool sample: Most people with diarrhoea do not need testing of stool sample. The doctor may recommend stool sample to investigate for bacteria or parasites if you have:
Blood tests: Blood tests may be conducted to rule out complications due to dehydration or if an underlying health condition is possibly causing your diarrhoea. For example, the doctor may recommend tests to check for blood urea and electrolytes (to look for dehydration or electrolyte imbalance), or tests to check for signs of inflammation which may suggest an inflammatory bowel disease.
In people with unexplained persistent diarrhoea, or those over 50 years old, the doctor may suggest a digital rectal examination. In this test the doctor inserts a finger into your anus (back passage) and rectum to check for abnormality in your rectum (such as growth).
Other tests: Tests such as sigmoidoscopy or colonoscopy may be required for people with persistent diarrhoea. During sigmoidoscopy a thin flexible tube called sigmoidoscope (which has an attached small camera and light) is inserted into your rectum, then up into your bowel to look for abnormality. If there is a suspicious lesion or growth, the doctor can take a biopsy from the region. In colonoscopy the entire large bowel can be examined.