What diagnostic tests are used for gastrointestinal (GI) symptoms?

Diagnostic Tests for Gastrointestinal Symptoms

The diagnostic approach for gastrointestinal symptoms should follow a stepwise algorithm starting with symptom assessment using validated tools, followed by laboratory tests including fecal calprotectin, endoscopic evaluation, and cross-sectional imaging when indicated.

Initial Symptom Assessment

Validated Assessment Tools

• Rome II Diagnostic Criteria for Irritable Bowel Syndrome (IBS) 1:

  • At least 12 weeks of abdominal discomfort/pain in the preceding 12 months with 2 of 3 features:
    1. Relief with defecation
    2. Onset associated with change in stool frequency
    3. Onset associated with change in stool form
  • Supporting symptoms: abnormal stool frequency/form/passage, mucus passage, bloating

• Clinical Symptom Evaluation:

  • Detailed symptom history including bowel patterns 1
  • Presence of alarm features (weight loss, nocturnal symptoms, bleeding, high-volume diarrhea, fevers)
  • Recent antibiotic use
  • Symptom duration
  • Physical examination for abdominal distension, masses, and rectal examination

Laboratory Tests

Basic Laboratory Workup

• Complete blood count - to assess for anemia, inflammation 1
• Liver profile and albumin - to evaluate nutritional status and liver function 1
• Iron studies - particularly in suspected IBD 1
• Renal function - baseline assessment 1
• Vitamin B12 - especially with chronic diarrhea 1
• C-reactive protein (CRP) - inflammatory marker, though up to 15% of IBD patients may have normal levels 1

Stool Tests

• Fecal calprotectin - key test to differentiate inflammatory from functional disorders 1:

  • Values < 50 μg/g suggest functional disorder
  • Values 50-250 μg/g are indeterminate
  • Values > 250 μg/g suggest active inflammation

• Fecal lactoferrin - alternative marker of intestinal inflammation 1

• Stool analysis and culture - for infectious causes 1

• C. difficile toxin testing - especially after antibiotic use 1

• Stool for ova, parasites, and fat globules - in suspected malabsorption 1

Endoscopic Evaluation

Ileocolonoscopy

• Indications:

  • All patients with suspected IBD 1
  • Patients > 45 years with IBS symptoms (to exclude colorectal cancer) 1
  • Patients with alarm features 1

• Procedure details:

  • Visualization of terminal ileum and all colonic segments 1
  • Precise description of lesions including type, location, depth, and extent 1
  • Biopsies from both affected and non-affected areas (at least two biopsies from each segment) 1

Upper GI Endoscopy

• Indications:
  • Upper GI symptoms 1
  • Particularly useful in pediatric patients 1
  • Suspected celiac disease

Video Capsule Endoscopy

• Indications:
  • Suspected small bowel pathology with inconclusive ileocolonoscopy and imaging 1
  • Particularly useful for obscure GI bleeding, suspected Crohn's disease, and celiac disease 1
  • Should be considered complementary to other tests 1

Cross-Sectional Imaging

MR Enterography

• First-line imaging modality for small bowel assessment where available 1
• Particularly important in Crohn's disease to assess extent and severity 1

CT Enterography

• Alternative when MRI is not available 1
• Higher radiation exposure (use cautiously in young patients) 1

Ultrasound

• May be useful where expertise exists 1
• Generally not recommended as first-line as it may detect incidental findings 1

Specialized Functional Tests

For Suspected Malabsorption

• Breath hydrogen test for lactose malabsorption - particularly in regular dairy consumers 1
• SeHCAT (bile acid absorption test) - in unexplained diarrhea with stool weights >200g 1

For Constipation

• Colonic transit studies - can identify slow transit constipation 2
• Anorectal manometry - to detect dyssynergic defecation 2
• Balloon expulsion test - simple test for rectal evacuation disorders 2
• Defecography - can identify structural abnormalities 2

Diagnostic Algorithm Based on Predominant Symptoms

For Diarrhea-Predominant Symptoms

1. Stool tests (calprotectin, culture, C. difficile)
2. Blood tests (CBC, CRP, celiac serology)
3. Colonoscopy with biopsies if calprotectin elevated or alarm features
4. Consider breath tests for carbohydrate malabsorption
5. Consider bile acid malabsorption testing in unexplained cases

For Constipation-Predominant Symptoms

1. Blood tests (thyroid function, calcium, glucose)
2. Colonoscopy if age >45 or alarm features
3. Consider transit studies if refractory to treatment
4. Anorectal function testing for suspected evacuation disorder

For Pain-Predominant Symptoms

1. Blood tests (CBC, liver function, amylase/lipase)
2. Upper endoscopy and/or colonoscopy based on symptoms
3. Cross-sectional imaging if structural cause suspected

Special Considerations

• Inflammatory vs. Functional Disorders: Fecal calprotectin is the most useful non-invasive test to differentiate 1
• Alarm Features: Prompt more extensive investigation including endoscopy and imaging 1
• Age Considerations: Lower threshold for endoscopy in patients >45 years 1
• Rectal Bleeding and Weight Loss: Associated with significantly higher rates of pathologic findings on imaging 3

By following this structured approach to diagnostic testing for gastrointestinal symptoms, clinicians can efficiently identify the underlying cause while minimizing unnecessary tests, leading to improved patient outcomes through appropriate treatment selection.