What tests should be ordered for a patient presenting with new onset bowel incontinence?

Initial Laboratory and Diagnostic Testing for New Onset Bowel Incontinence

For new onset bowel incontinence, begin with basic laboratory screening including complete blood count, inflammatory markers (CRP or ESR), stool studies for infectious causes (C. difficile, bacterial culture, ova and parasites if indicated), and fecal calprotectin to exclude inflammatory bowel disease, followed by anorectal manometry as the primary functional test. 1, 2

Essential Initial Laboratory Tests

Core Blood Work

• Complete blood count (CBC) to screen for anemia (which may indicate chronic blood loss from inflammatory bowel disease or malignancy) and leukocytosis (suggesting infection or inflammation) 3, 4
• C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR) to assess for occult inflammation, though approximately 20% of patients with active Crohn's disease may have normal CRP levels 5, 3, 4
• Serum chemistries and albumin to evaluate nutritional status and electrolyte abnormalities that may contribute to diarrhea 5, 6

Critical Stool Studies

• C. difficile testing in all patients before initiating any immunosuppressive therapy 5
• Stool bacterial culture or comprehensive stool pathogen panel to exclude infectious colitis 5
• Fecal calprotectin or fecal lactoferrin to screen for inflammatory bowel disease, particularly in patients under age 45 3, 4
• Stool for ova and parasites only if travel history to or recent immigration from endemic areas 3, 4

Additional Testing Based on Clinical Context

• Fecal elastase with qualitative fecal fat testing if steatorrhea is present or if patient does not respond to typical treatments, as immune-mediated pancreatic insufficiency is an uncommon but important cause 5
• Celiac serology (IgA tissue transglutaminase with total IgA) if diarrhea is a prominent feature, as celiac disease can present with fecal incontinence 3, 4

Anorectal Function Testing

Primary Functional Assessment

High-resolution anorectal manometry should be the first investigatory tool for fecal incontinence after basic laboratory screening, as it assesses sphincter pressures, rectal sensation, and rectoanal coordination. 2, 7 This test is particularly valuable because clinical assessment alone misdiagnoses up to 20% of patients with fecal incontinence. 8

Structural Imaging

• Endoanal ultrasound to evaluate for internal anal sphincter defects, which are often clinically unsuspected and alter management in 16% of cases 8, 2
• Magnetic resonance imaging (MRI) of the pelvis for external anal sphincter injury and pelvic floor anatomical disturbances 2, 7
• Defecography (fluoroscopic or MR) if evacuation disorder is suspected based on manometry findings 7, 9

Neurophysiological Testing

• External sphincter electromyography (EMG) to assess for neuropathy, particularly useful in separating neuropathic causes from structural disorders 8, 7

Age-Specific and Risk-Based Testing

Colonoscopy Indications

• Patients over age 50 years should undergo colonoscopy regardless of symptom pattern due to higher pretest probability of colon cancer 5, 4
• Any patient with alarm features including rectal bleeding, significant weight loss, or family history of inflammatory bowel disease or colorectal cancer requires colonoscopy 4
• Younger patients without alarm features do not require colonoscopy if fecal calprotectin is normal 3

Stepwise Diagnostic Algorithm

Step 1: Initial Clinical Assessment with Basic Labs

Obtain CBC, CRP/ESR, comprehensive metabolic panel, stool studies (C. difficile, culture, calprotectin), and stool occult blood. 3, 4, 1

Step 2: Anorectal Manometry

Proceed to high-resolution anorectal manometry as the primary functional test to assess sphincter function, rectal sensation, and coordination. 2, 7

Step 3: Structural Imaging Based on Manometry Results

• If sphincter weakness is identified: endoanal ultrasound for internal sphincter defects 2
• If external sphincter dysfunction: pelvic MRI for external sphincter and pelvic floor assessment 2, 7
• If evacuation disorder suspected: defecography 7, 9

Step 4: Neurophysiological Testing if Indicated

EMG testing if neuropathy is suspected based on manometry findings or clinical features (diabetes, neurological disease, obstetrical injury). 8, 7

Common Pitfalls to Avoid

• Do not rely on clinical assessment alone, as experienced clinicians miss surgically correctable causes in up to 19% of cases without objective testing 8
• Do not skip infectious workup before considering immunosuppressive therapy, as this can lead to catastrophic complications 5
• Do not assume normal inflammatory markers exclude inflammatory bowel disease, particularly in Crohn's disease where 20% have normal CRP 5
• Do not order ultrasound of the abdomen as a screening test, as it often detects incidental findings unrelated to symptoms 3
• Do not perform colonoscopy in young patients (<45 years) with typical functional symptoms and no alarm features if fecal calprotectin is normal 3