What is Diarrhea ?
Diarrhea is recent change in consistency or frequency of stool. Acute diarrhea is less than 14 days in duration. Chronic diarrhea is defined as more 4 weeks in duration.

Causes / Acute:
Chronic
Irritable bowel syndrome
Evaluation
Requirement of evaluation depends on the duration and severity of diarrhea. Work up may include complete blood count, serum electrolytes, blood sugar, thyroid function tests and/or tests for celiac disease. Stool tests may be required to search for an infectious agent / to characterize type of diarrhea. Occasionally, you may require collecting stools for 3 days in order to indentify atypical infection/fat malabsorption.
A flexible sigmoidoscopy or colonoscopy may be required, but this depends on age, severity/duration of symptoms.
Breath tests may be required to diagnose conditions such as bacterial overgrowth and lactose intolerance.
Treatment
It depends on the cause of diarrhea. Mild symptoms can manage at home. Moderate to severe symptoms may need medical evaluation and occasionally hospitalization.
Mild symptoms:
Moderate to severe symptoms
(Abdominal pain, fever, bloody stool and symptoms of dehydration).