gastrointestinal disorders
Diarrhea
Evaluation of Diarrhea
History of present illnessshould determine duration and severity of diarrhea, circumstances of onset (including recent travel, food ingested, source of water), drug use (including any antibiotics within the previous 3 months), abdominal pain or vomiting, frequency and timing of bowel movements, changes in stool characteristics (eg, presence of blood, pus, or mucus; changes in color or consistency; evidence of steatorrhea), associated changes in weight or appetite, and rectal urgency or tenesmus should be noted. Simultaneous occurrence of diarrhea in close contacts should be ascertained. Physicians should ask specifically about any changes in drugs that may cause diarrhea. Review of systemsshould seek symptoms suggesting possible causes, including joint pains (inflammatory bowel disease, celiac disease), flushing (carcinoid, vipoma, mastocytosis), chronic abdominal pain (irritable bowel, inflammatory bowel disease, gastrinoma), and GI bleeding (ulcerative colitis, tumor). Past medical historyshould identify known risk factors for diarrhea, including inflammatory bowel disease, irritable bowel syndrome, HIV infection, and previous GI surgical procedures (eg, intestinal or gastric bypass or resection, pancreatic resection). Family and social history should query about simultaneous occurrence of diarrhea in close contacts. Fluid and hydration status should be evaluated. A full examination with attention to the abdomen and a digital rectal examination for sphincter competence and occult blood testing are important. Certain findings raise suspicion of an organic or more serious etiology of diarrhea: Blood or pus in stool Fever Signs of dehydration Chronic diarrhea Weight loss Acute, watery diarrheain an otherwise healthy person is likely to be of infectious etiology, particularly when travel, possibly tainted food, or an outbreak with a point-source is involved. with or without hemodynamic instability in an otherwise healthy person suggests an enteroinvasive infection. Diverticular bleeding and ischemic colitis also manifest with acute bloody diarrhea. Recurrent bouts of bloody diarrhea in a younger person suggest Overview of Inflammatory Bowel Disease . 1 L/day) strongly suggests an endocrine tumor cause in patients with normal GI anatomy. A history of oil droplets in stool, particularly if associated with weight loss, suggests Overview of Malabsorption . Diarrhea that consistently follows ingestion of certain foods (eg, fats) suggests food intolerance. Recent antibiotic use should raise suspicion for antibiotic-associated diarrhea, including Clostridioides (formerly Clostridium) difficile–Induced Diarrhea (formerly Diarrhea with green or orange stools suggests impaired absorption of bile salts. The symptoms can help identify the affected part of the bowel. Generally, in small-bowel diseases, stools are voluminous and watery or fatty. In colonic diseases, stools are frequent, sometimes small in volume, and possibly accompanied by blood, mucus, pus, and abdominal discomfort. In Irritable Bowel Syndrome (IBS) (IBS), abdominal pain is related to defecation, associated with changes in stool frequency or consistency, or both. However, these symptoms alone do not discriminate IBS from other diseases (eg, inflammatory bowel disease). Functional diarrhea is characterized by loose or watery stools with onset at least 6 months before diagnosis and present during the previous 3 months. These patients do not meet the criteria for IBS; they may have abdominal pain and/or bloating, but these are not predominant symptoms ( Extra-abdominal findings that suggest an etiology include skin lesions or flushing ( Mastocytosis and Mast Cell Activation Syndrome ), thyroid nodules ( Acute diarrhea (<4 days) typically does not require testing. Exceptions are patients with signs of dehydration, bloody stool, fever, severe pain, hypotension, or toxic features—particularly those who are very young or very old. These patients should have a complete blood count and measurement of electrolytes, bloodureanitrogen, and creatinine. Stool samples should be collected for microscopy, culture, and, if antibiotics have been taken recently,C. difficiletoxin assay. Chronic diarrhea (>4 weeks) requires evaluation, as does a shorter (1 to 3 weeks) bout of diarrhea in immunocompromised patients or those who appear significantly ill. Diagnostic evaluation should be directed by the history and physical examination when possible. If this approach does not provide a diagnosis or direction, a broader approach is needed. Initial testing should include stool for occult blood, fat (by Sudan stain or fecal elastase), electrolytes (to calculate the stool osmotic gap), andGiardiaantigen or polymerase chain reaction test; complete blood count with differential; celiac serology (IgA tissue transglutaminase); thyroid-stimulating hormone (TSH) and free thyroxine (T4); and fecal calprotectin or fecal lactoferrin (to screen for inflammatory bowel disease [IBD]). The 2019 American Gastroenterological Association'sguidelines on the laboratory evaluation of functional diarrhea and diarrhea-predominant IBS (IBS-D)recommend a threshold value of 50 mcg/g for fecal calprotectin or a range of 4.0 to 7.25 mcg/g for fecal lactoferrin to optimize sensitivity for IBD. Microscopic examination for ova and parasites should be done for patients with recent travel history to or recent immigration from high-risk areas. Stool tests forC. difficileshould be done in patients with recent antibiotic exposure or suspectedC. difficileinfection. Sigmoidoscopy or colonoscopy with biopsies should follow to look for inflammatory causes. If no diagnosis is apparent and Sudan stain or fecal elastase is positive for fat, fecal fat excretion should be measured. Additional testing, including small-bowel CT enterography (structural disease) and endoscopic small-bowel biopsy (mucosal disease), can be considered (eg, if symptoms persist or are severe such as weight loss). If evaluation still yields negative findings, assessment of pancreatic structure and function ( see Laboratory tests ) should be considered for patients who have unexplained steatorrhea. Infrequently, capsule endoscopy may uncover lesions, predominantly Crohn disease or nonsteroidal anti-inflammatory drug enteropathy, not identified by other modalities. The stool osmotic gap, which is calculated 290−2×(stool sodium+stool potassium), indicates whether diarrhea is secretory or osmotic. An osmotic gap<50 mEq/L indicates secretory diarrhea; a larger gap suggests osmotic diarrhea. Patients with osmotic diarrhea may have covert magnesium laxative ingestion (detectable by stool magnesium levels) or carbohydrate malabsorption (diagnosed by hydrogen breath test,lactaseassay, and dietary review). Undiagnosed secretory diarrhea requires testing (eg, plasma gastrin,calcitonin, vasoactive intestinal peptide levels, histamine, urinary 5-hydroxyindoleacetic acid[5-HIAA]) for endocrine-related causes. A review for symptoms of adrenal insufficiency should be done. Surreptitious laxative abuse must be considered; it can be ruled out by a fecal laxative assay. 1.Lacy BE, Mearin F, Chang L, et al: Bowel disorders.Gastroenterology150(6):1393–1407, 2016. doi: 10.1053/j.gastro.2016.02.031 