Chronic diarrhea can be a severely debilitating condition and a common chief concern prompting patients to seek medical attention. The American College of Gastroenterology defines chronic diarrhea as loose or watery stool lasting longer than four weeks.¹ Persistent diarrhea lasts between two to four weeks, and diarrhea lasting less than two weeks is considered acute.¹ Acute and persistent diarrhea typically result from infection (eg, parasites, bacteria, and viral) or ingestion of osmotic substances and are both often self-limiting, whereas chronic diarrhea is more challenging to diagnose and persists unless therapy is initiated.^2-4 A broad differential diagnosis enables practitioners to avoid missing common etiologies; and the likelihood of identifying the root cause(s), whether structural, functional, or infectious, significantly increases when combined with a systematic history and clinical reasoning of physical exams and labs. However, diagnostic work-up and lab testing can become costly and complicated, increasing the risk of delayed or improper treatment. Chronic diarrhea can differ in etiology for pediatric, adult, and geriatric patient populations. Lab testing and treatment approaches should be chosen based on age, history, stool patterns, and characteristics of the disease process.³ This essay aims to inform readers of the recommendations outlined in the most recent guidelines for diagnosing chronic diarrhea, review some unique etiologies of chronic diarrhea to have on the differential, and describe a few approaches to therapeutic intervention.

The American Gastroenterology Association (AGA) and the British Society of Gastroenterology (BSG) recently published guidelines to help clinicians choose appropriate investigative lab tests and treatment approaches when patients present with chronic diarrhea. The goal is to enable more primary care clinicians to better support patients with this chief concern, mitigate the financial strain of unnecessary testing, provide timely diagnosis and treatment, and reduce specialist burden.^5,6 Focusing the differential begins with a thorough interview, physical exam, and preliminary testing. Characteristic alarm features warranting colonoscopy or flexible sigmoidoscopy include diarrheal onset after age 50, melena or hematochezia, nocturnal pain, progressive abdominal pain, unexplained weight loss, and family history of colorectal cancer.⁵ Asking patients to report the quality of their stool based on the Bristol Stool Form Scale, whether they notice blood, mucus, or undigested food, and the frequency of episodes will help the clinician characterize the stool pattern into infectious, inflammatory, fatty, or watery, with secretory or osmotic subtypes.³ Inquiring about stool changes over time, and a dietary history, will also provide useful information for narrowing the differential and focusing testing.