In addition, hydrogen breath tests may be used to diagnose SIBO. Small bowel aspiration can be performed to look for SIBO, which causes steatorrhea by deconjugation of bile acids with resultant low duodenal bile acid concentrations. Endoscopy with small bowel biopsies allows evaluation of the small intestinal mucosa for celiac disease. The evaluation focuses on looking for a structural problem involving the small intestine or pancreas. When fatty diarrhea is identified, the initial goal is to distinguish malabsorption from maldigestion. However, the criterion standard for steatorrhea is a quantitative measurement on a timed stool collection while patients consume a 100-g fat diet, and steatorrhea is defined as more than 7 g of fat per 24 hours.

A simple test to screen for excess fecal fat is a Sudan stain, which will detect most cases of clinically significant steatorrhea. Malabsorption is caused by mucosal diseases, most commonly celiac disease, whereas the maldigestion results from pancreatic exocrine insufficiency (eg, chronic pancreatitis) or inadequate duodenal bile acid concentration (eg, small intestinal bacterial overgrowth or cirrhosis). Fat malabsorption results from inadequate mucosal transport, and fat maldigestion results from defective hydrolysis of triglycerides. The basic mechanisms of chronic fatty diarrhea are malabsorption and maldigestion. When history or stool analysis suggests chronic inflammatory diarrhea, flexible sigmoidoscopy or colonoscopy should be the initial study to look for structural changes. Radiation colitis and neoplasia are uncommon causes of inflammatory diarrhea. Inflammatory diarrhea fundamentally indicates disrupted and inflamed mucosa, such as that caused by idiopathic inflammatory bowel disease (Crohn disease or ulcerative colitis), ischemic colitis, and infectious processes, such as C difficile, cytomegalovirus, tuberculosis, or Entamoeba histolytica. Other laboratory studies that may indicate an inflammatory diarrhea include elevated C-reactive protein level or sedimentation rate and low serum albumin level. Inflammatory diarrhea is suspected with the demonstration of leukocytes or leukocyte proteins (eg, calprotectin or lactoferrin) on stool examination. Inflammatory diarrhea is characterized by frequent, small-volume, bloody stools and may be accompanied by tenesmus, fever, or severe abdominal pain. Categorize the Diarrhea as Inflammatory, Fatty, or Watery In contrast to acute diarrhea, chronic diarrhea typically warrants a diagnostic evaluation, is less likely to resolve on its own, and presents a broad differential diagnosis. However, stool testing and other studies are often indicated in the presence of certain clinical or epidemiological features, including age older than 65 years, immune compromise, volume depletion, hematochezia or blood-tinged stool, fever, severe abdominal pain, recent antibiotic use, known or suspected inflammatory bowel disease, community infectious disease outbreaks, and employment as a food handler.

Often, no evaluation or treatment is required. The approach to acute diarrhea is straightforward because it is most commonly caused by infection and is self-limited. Diarrhea is acute if it lasts fewer than 2 weeks and chronic if it lasts more than 4 weeks.

The duration of diarrhea may be an important clue to the cause. If a drug-induced cause of diarrhea seems unlikely, then the third step that can help direct evaluation is the duration of the diarrhea.

Diarrhea close to due date