What labs are recommended for a 29-year-old presenting to the Emergency Room (ER) with 3 weeks of constipation?

Laboratory Testing for a 29-Year-Old with 3 Weeks of Constipation in the ER

For a 29-year-old presenting to the ER with 3 weeks of constipation, a complete blood count is the only laboratory test strongly recommended in the initial evaluation. 1, 2

Initial Laboratory Assessment

Recommended Tests:

• Complete Blood Count (CBC) - Strongly recommended as the primary screening test 1, 2

Tests to Consider Based on Clinical Presentation:

• Metabolic tests are generally not routinely recommended unless specific clinical features warrant them 1, 2:
  • Thyroid-stimulating hormone (TSH) - If symptoms of hypothyroidism present
  • Serum glucose - If diabetes suspected
  • Serum calcium - If hypercalcemia suspected
  • Serum creatinine - If renal dysfunction suspected

Clinical Evaluation Focus Points

History and Physical Examination:

• Assess for "alarm signs" or "red flags" that would necessitate more extensive evaluation 1:
  • Fever
  • Weight loss
  • Blood in stools
  • Anemia
  • Family history of inflammatory bowel disease or colorectal cancer

Digital Rectal Examination:

• Perform a thorough digital rectal examination that includes 1, 2:
  • Assessment of pelvic floor motion during simulated evacuation
  • Evaluation of resting sphincter tone and its augmentation during squeeze
  • Assessment of the puborectalis muscle
  • Request that the patient "expel your finger" to evaluate expulsionary forces

Imaging and Additional Testing

Structural Evaluation:

• Colonoscopy is not recommended for this 29-year-old patient unless 1, 2, 3:
  • Alarm features are present (blood in stools, anemia, weight loss)
  • There is an abrupt onset of constipation
  • Family history of colorectal cancer exists

Specialized Testing (if initial management fails):

• Anorectal manometry and balloon expulsion test 2
• Colonic transit study if defecatory disorders are ruled out 1, 2

Management Algorithm

1. Initial laboratory testing: Complete blood count
2. Evaluate for medication side effects: Review current medications that may cause constipation
3. Initial management: Trial of fiber and/or over-the-counter laxatives
4. If no response to initial management:
   • Consider specialized testing for defecatory disorders
   • Evaluate colonic transit if defecatory disorders are ruled out

Important Considerations

• The diagnostic utility and cost-effectiveness of routine metabolic tests (TSH, glucose, calcium) have not been rigorously evaluated and are probably low in young patients without specific symptoms suggesting metabolic disorders 1
• A normal digital rectal examination does not exclude defecatory disorders, which are a common cause of constipation 1
• Patients with chronic constipation who do not respond to initial measures may benefit from specialized testing and treatments 1

This approach balances the need for appropriate screening while avoiding unnecessary testing in a young patient with constipation, focusing on tests that will most impact morbidity, mortality, and quality of life outcomes.