What labs are recommended for diagnosing a gastric ulcer?

Laboratory Testing for Gastric Ulcer Diagnosis

Routine laboratory studies and arterial blood gas analysis are strongly recommended in patients with suspected gastric ulcer, though these tests are non-specific and primarily useful for detecting complications like perforation rather than diagnosing uncomplicated ulcers. 1, 2

Laboratory Studies for Suspected Gastric Ulcer

Non-Specific Laboratory Tests

For patients presenting with acute symptoms suggestive of complicated gastric ulcer (perforation or bleeding):

• Routine laboratory studies including complete blood count, metabolic panel, and arterial blood gas analysis should be obtained 1, 2
• Leukocytosis, metabolic acidosis, and elevated serum amylase are commonly associated with gastric perforation, though these findings are non-specific 1, 2
• These tests help assess disease severity and guide resuscitation but do not confirm the diagnosis of gastric ulcer itself 1

Helicobacter pylori Testing (Essential for Diagnosis)

All patients with suspected or confirmed gastric ulcer should undergo H. pylori testing, as this identifies the underlying cause and guides curative treatment. 1

Non-Invasive H. pylori Tests (Preferred):

• Urea breath test (UBT): Sensitivity 88-95%, specificity 95-100% for active infection 1
• Stool antigen test: Sensitivity 94%, specificity 92% for active infection 1
• These tests detect active infection and are the preferred non-invasive methods 1, 3

Important Caveats for H. pylori Testing:

• Stop proton pump inhibitors (PPIs), antibiotics, and bismuth products for at least 2 weeks before testing to avoid false-negative results 1
• Histamine-2 receptor antagonists do not affect bacterial load and can be substituted for PPIs during this period 1
• A positive test can be trusted even if medications weren't stopped, but negative results may be false negatives 1

Serology (Limited Role):

• IgG serology is generally not recommended as it cannot distinguish active from past infection and remains positive long after eradication (serologic "scar") 1
• Only use serology when there is very high pretest probability (e.g., active duodenal ulcer), and confirm active infection with UBT or stool antigen test before treatment 1
• Avoid IgA and IgM tests - these are not FDA-approved and have low specificity and sensitivity 1

Diagnostic Algorithm

For Uncomplicated Gastric Ulcer:

1. Endoscopy with biopsy remains the gold standard for diagnosing gastric ulcer, as it allows visualization, biopsy to exclude malignancy, and H. pylori testing 2, 4
2. During endoscopy, perform rapid urease test, histology, or culture for H. pylori detection 4, 3
3. If endoscopy is not immediately available or indicated, use non-invasive H. pylori testing (UBT or stool antigen) 1

For Suspected Perforated Gastric Ulcer:

1. Obtain routine labs and arterial blood gas immediately 1, 2
2. CT scan is the preferred imaging modality (strong recommendation) 1, 2
3. If CT unavailable, perform chest/abdominal X-ray to detect free air 1, 2
4. H. pylori testing should still be performed in all bleeding or perforated ulcer patients to guide post-operative eradication therapy 1

For Bleeding Gastric Ulcer:

1. No empirical antibiotics are recommended 1
2. H. pylori testing is mandatory in all bleeding peptic ulcer patients 1
3. Testing can be done via endoscopic biopsy during therapeutic endoscopy, or non-invasively with UBT or stool antigen test 1

Common Pitfalls

• Do not rely on serology alone for treatment decisions - it cannot confirm active infection 1
• Do not forget to stop PPIs before testing - this is the most common cause of false-negative H. pylori tests 1
• All gastric ulcers require biopsy to exclude malignancy, even with negative H. pylori testing 5
• Laboratory tests alone cannot diagnose gastric ulcer - they only detect complications or associated findings 1, 2