| Clinical or laboratory features | Potential etiology |
| History | |
| Symptom characteristics | |
| Leakage of stool | Fecal incontinence |
| Onset: | |
| Congenital | Chloridorrhea, Na+ malabsorption |
| Abrupt | Infections, idiopathic secretory diarrhea |
| Gradual | Everything else |
| Nocturnal diarrhea | Secretory or inflammatory diarrhea |
| Stool characteristics: | |
| Blood | Malignancy, inflammatory bowel disease |
| Oil droplets | Malabsorption, maldigestion |
| White/tan color | Celiac disease, absence of bile |
| Stool volume: | |
| Small volume, frequent | Colonic etiology |
| Large volume | Small bowel etiology |
| Associated symptoms | |
| Weight loss | Malabsorption, pancreatic exocrine insufficiency, neoplasm |
| Abdominal pain | Mesenteric vascular insufficiency, obstruction, irritable bowel syndrome |
| Bloating and flatus | Carbohydrate malabsorption |
| Systemic symptoms | Hyperthyroidism, diabetes, neoplasia, tuberculosis, adrenal insufficiency, mastocytosis, vasculitis, Whipple's disease |
| Joint pain/arthritis | Inflammatory bowel disease, yersiniosis |
| Risk factors | |
| Medications | Medication-associated diarrhea (eg, metformin), infection (eg, Clostridioides difficile), enteropathy (eg, olmesartan) |
| Radiation | Radiation enteritis, small intestinal bacterial overgrowth, enteroenteric fistula |
| Abdominal surgery | Altered motility, post-cholecystectomy diarrhea, small intestinal bacterial overgrowth, bile acid malabsorption, short bowel syndrome |
| Hematopoietic cell transplant | Graft versus host disease, cord-colitis syndrome (recipient of umbilical cord blood transplantation only) |
| Diabetes mellitus | Altered motility, small intestinal bacterial overgrowth, medications associated with diarrhea, pancreatic exocrine insufficiency, or associated celiac disease |
| Immunocompromised host | Infectious diarrhea (eg, Microsporidium, Cryptosporidium, Cytomegalovirus infection), lymphoma |
| Recurrent bacterial infections | HIV/AIDS, immunoglobulin deficiencies |
| Diet: | |
| Sugar-free foods | Sorbitol, mannitol ingestion |
| Raw milk | Brainerd diarrhea |
| Food additives (eg, fructose) | Fructose intolerance |
| FODMAPs | Irritable bowel syndrome |
| Dairy | Lactase deficiency |
| Exposure to contaminated food or water source | Chronic infections (eg, Aeromonas, Giardia, Cryptosporidium, E. histolytica), Brainerd diarrhea |
| Antibiotic or healthcare exposure | Clostridioides difficile infection, fecal impaction with overflow diarrhea, ischemic colitis |
| Travel | Infectious diarrhea, chronic idiopathic secretory diarrhea, post-infectious irritable bowel syndrome |
| Secondary gain from illness | Laxative abuse |
| Family history | Congenital absorptive defects, inflammatory bowel disease, celiac disease, multiple endocrine neoplasia |
| Physical examination | |
| Muscle wasting, peripheral edema | Malnutrition |
| Urticaria pigmentosa, dermatographism | Mast cell disease (mastocytosis) |
| Pinch purpura, macroglossia | Amyloidosis |
| Hyperpigmentation, postural hypotension | Primary adrenal insufficiency (Addison's disease) |
| Migratory necrotizing erythema | Glucagonoma |
| Dermatitis herpetiformis | Celiac disease |
| Erythema nodosum, pyoderma gangrenosum | Inflammatory bowel disease |
| Flushing, heart murmur, wheezing | Carcinoid syndrome |
| Thyroid nodule, tremor, lid lag | Hyperthyroidism |
| Lymphadenopathy | HIV, lymphoma, cancer |
| Hepatomegaly | Endocrine tumor, amyloidosis |
| Splenomegaly | Mastocytosis, Whipple's disease, extranodal marginal zone lymphoma of mucosa associated lymphoid tissue (MALT lymphoma) |
| Abdominal bruit | Chronic mesenteric ischemia |
| Anal sphincter weakness | Fecal incontinence |
| Laboratory tests | |
| Anemia | Celiac disease, inflammatory bowel disease, malabsorption |
| Elevated anti-tissue transglutaminase antibody | Celiac disease |
| Elevated ESR/CRP | Active inflammatory process (nonspecific) |
| Elevated fecal calprotectin | Inflammatory diarrhea |
| Positive stool test for occult blood | Organic disease (eg, chronic infection or inflammatory bowel disease) |
