The most appropriate management is outpatient follow-up. This patient meets four criteria for nonadmission with outpatient follow-up based on the 2008 Scottish Intercollegiate Guidelines Network (SIGN) (www.sign.ac.uk/pdf/sign105.pdf). These criteria include age less than 60 years, no hemodynamic instability, no evidence of gross rectal bleeding, and identification of an obvious anorectal source of bleeding on rectal examination or sigmoidoscopy.

Admission to the hospital for observation is not necessary because this patient's bleeding is attributable to a specific, minor cause of lower gastrointestinal bleeding, namely an anal fissure that is appropriate for outpatient management. The diagnosis is based on physical findings and a compelling clinical history. Anal fissures are tears in the anal skin distal to the dentate line; they may therefore be exquisitely painful, particularly with defecation. They are most often caused by local trauma such as hard stools. Anoscopy or direct visualization typically reveals a small mucosal tear, most often in the posterior midline. Hospitalization should be considered in patients with any of the following five criteria that predict severe bleeding: age 60 years or older, comorbid illnesses (particularly when two or more are present), hemodynamic instability, gross rectal bleeding (or early rebleeding), or exposure to antiplatelet drugs and anticoagulants.

Colonoscopy within 12 to 18 hours is not appropriate because this patient's clinical status does not warrant urgent or emergent investigations based on the SIGN guidelines. Elective colonoscopy or sigmoidoscopy might be performed on an outpatient basis to exclude causes other than chronic constipation, such as proctitis from inflammatory bowel disease or infection (such as herpesvirus or HIV).

Surgery is not necessary because this option is typically offered for chronic rather than acute anal fissures and only after exhausting medical options.