What labs should be ordered for suspected peptic ulcer disease (PUD)?

Laboratory Tests for Suspected Peptic Ulcer Disease

For patients with suspected peptic ulcer disease (PUD), routine laboratory studies including complete blood count, coagulation profile, and testing for Helicobacter pylori infection should be ordered as the initial diagnostic workup. 1

Initial Laboratory Workup

Basic Laboratory Tests

• Complete blood count (CBC) with differential
  • To assess for anemia which may indicate chronic blood loss
  • Leukocytosis may suggest inflammation or perforation
• Coagulation profile (PT, aPTT)
  • To evaluate bleeding risk and coagulation status
• Serum electrolytes
• Blood urea nitrogen (BUN) and creatinine
  • Elevated BUN may indicate upper GI bleeding (due to blood protein breakdown in the gut)
• Arterial blood gas analysis (in cases of suspected perforation)
  • To detect metabolic acidosis which may accompany perforation 1

H. pylori Testing

H. pylori testing is crucial as it is a major cause of PUD and its eradication significantly reduces the risk of recurrence and complications. The following tests are available:

1. Urea Breath Test (UBT)

   • Recommended as first-line test in bleeding PUD patients
   • Highest sensitivity (89-100%) on first day of presentation
   • Most cost-effective strategy for identifying H. pylori 2

2. Endoscopic-based tests (if endoscopy is performed)

   • Rapid urease test (CLO test)
     • Limited sensitivity (67.8%) during active bleeding
   • Histology
     • Sensitivity around 75% during active bleeding 3

3. Non-invasive tests

   • Stool antigen test
   • Serology (antibody testing)
     • High sensitivity (100%) but cannot distinguish between active and past infection 3

Additional Tests Based on Clinical Presentation

For Suspected Perforation

• Serum amylase
  • May be elevated in perforated PUD 1
• Liver function tests
  • To rule out other causes of abdominal pain

For Suspected Bleeding

• Type and cross-match for blood products
  • Essential if active bleeding is suspected
• Shock index calculation (heart rate/systolic blood pressure)
  • Value >1 indicates hemodynamic instability 4

Imaging Studies

While not laboratory tests, the following imaging studies are often ordered alongside laboratory tests:

• CT scan (preferred first-line imaging for suspected perforation)
• Chest/abdominal X-ray (if CT not promptly available)
  • To detect free air indicating perforation 1

Testing Algorithm

1. Initial presentation with suspected PUD:

   • Order CBC, coagulation profile, electrolytes, BUN/creatinine
   • Order urea breath test for H. pylori (highest sensitivity and cost-effectiveness)

2. If endoscopy is planned:

   • Add histology and rapid urease test for H. pylori detection
   • Note: These tests have lower sensitivity during active bleeding

3. If perforation is suspected:

   • Add arterial blood gas analysis and serum amylase
   • Order appropriate imaging (CT scan preferred)

Common Pitfalls to Avoid

• False negatives in H. pylori testing during active bleeding

  • Biopsy-based tests (histology, rapid urease test) have reduced sensitivity during active bleeding
  • Consider urea breath test or serology in these cases 3

• Relying solely on a single H. pylori test

  • Consider confirming negative results with a second method, especially if the clinical suspicion is high

• Delaying testing for H. pylori

  • Early detection and eradication reduces risk of rebleeding and other complications 5

• Overlooking NSAID use

  • Even with negative H. pylori tests, NSAID use is a common cause of PUD
  • Document all medication use, including over-the-counter NSAIDs 6

Remember that laboratory tests should be interpreted in the context of the patient's clinical presentation, and endoscopy remains the gold standard for definitive diagnosis of PUD.