What tests are used to evaluate constipation?

Diagnostic Tests for Constipation

The initial evaluation of constipation should include a complete blood cell count, while metabolic tests (glucose, calcium, thyroid-stimulating hormone) are not routinely recommended unless specific clinical features warrant them. 1

Initial Assessment

• A thorough digital rectal examination that includes assessment of pelvic floor motion during simulated evacuation is essential and should be performed before ordering specialized tests 1, 2
• The digital rectal examination should evaluate:
  • Sphincter tone
  • Tenderness
  • Presence of impacted feces
  • Obstructions or masses
  • Assessment of pelvic floor motion during simulated evacuation 1
• A normal digital rectal examination does not exclude defecatory disorders, so further testing may still be needed 1

Basic Laboratory Testing

• Complete blood cell count is the only necessary laboratory test in the absence of other symptoms and signs 1, 2
• Metabolic tests (glucose, calcium, thyroid-stimulating hormone) are not recommended for routine evaluation of chronic constipation unless clinical features suggest metabolic causes 1, 2
• If clinically suspected, corrected calcium levels and thyroid function should be checked 1

Structural Evaluation

• Colonoscopy should be performed only when alarm features are present: 1, 3
  • Blood in stools
  • Anemia
  • Weight loss
  • Abrupt onset of constipation
  • Age over 50 years without previous colorectal cancer screening 1, 2
• Alternative structural imaging options include: 1, 2
  • CT colonography (when colonoscopy is contraindicated)
  • Flexible sigmoidoscopy with barium enema 1, 2
• Plain abdominal radiographs have limited utility for diagnosing constipation and should not be relied upon as the sole diagnostic test 2, 4

Specialized Testing for Refractory Constipation

• Colonic transit studies should be performed if: 1
  • Anorectal test results do not show a defecatory disorder, or
  • Symptoms persist despite treatment of a defecatory disorder 1
• Anorectal manometry is indicated for patients with suspected defecatory disorders, with studies showing prevalence of dyssynergia in 20-75% of constipated patients 5, 4
• Balloon expulsion test is a simple method to assess for defecatory disorders, with studies showing impaired expulsion in 23-67% of constipated patients 4
• Defecography (fluoroscopic or MR) should be considered for suspected pelvic floor dysfunction, with studies reporting abnormalities in 25-90% of patients with chronic constipation 5, 4

Advanced Testing for Medically Refractory Cases

• Colonic manometry and barostat testing may be required for patients who do not respond to standard approaches, though these tests are only available at specialized centers 1, 6
• MR defecography provides high soft-tissue contrast resolution for visualization of pelvic organs and floor muscles in cases of suspected defecatory dysfunction 2

Common Pitfalls to Avoid

• Ordering colonoscopy for all patients with constipation without alarm features 1, 3
• Relying solely on plain abdominal radiographs for diagnosis 2, 4
• Failing to consider functional disorders when structural imaging is normal 2, 6
• Overlooking the need for structural evaluation in high-risk patients with alarm symptoms 1, 2, 3
• Ordering excessive testing without clear clinical indications 1, 2