A 38-year-old woman on chronic low-dose aspirin for primary prevention presents with a 3-month history of recurrent epigastric pain and nausea. Upper endoscopy shows a 1.5 cm antral ulcer with clean base. Rapid urease test (CLO test) is negative. What is the most appropriate next investigation to exclude H. pylori infection before stopping aspirin?

Explanation

## Confirming H. pylori Status When CLO Test is Negative ### Clinical Scenario A negative CLO test (rapid urease test) does not exclude H. pylori infection, especially if: - The patient is on a PPI or H~2~-blocker (reduces bacterial load, false-negative CLO) - The ulcer is in the antrum (lower bacterial density than fundus) - There is patchy infection In this case, the CLO test is negative, but H. pylori status must be confirmed before attributing the ulcer solely to aspirin and continuing the drug. ### Why Urea Breath Test is the Answer **Key Point:** The urea breath test (^13^C-urea or ^14^C-urea) is a non-invasive, highly sensitive and specific test for active H. pylori infection. It is the gold standard for confirming H. pylori when endoscopic tests are inconclusive. **High-Yield:** UBT has sensitivity 95–98% and specificity 95–98%. It detects active infection (not past exposure) and is unaffected by PPI use if the drug is stopped 2 weeks prior to testing. **Clinical Pearl:** In a patient with a negative CLO test but persistent symptoms and an ulcer, UBT is preferred because: 1. It is non-invasive (no need for repeat endoscopy) 2. It detects active infection reliably 3. It guides the decision: if positive → eradicate H. pylori AND stop aspirin; if negative → aspirin is the culprit → switch to alternative antiplatelet agent ### Comparison of H. pylori Diagnostic Tests | Test | Sensitivity | Specificity | Invasive | Active Infection | Timing | |---|---|---|---|---|---| | **Urea breath test** | 95–98% | 95–98% | No | Yes | Non-invasive, 30 min | | **Serology (IgG)** | 85–95% | 80–90% | No | No (detects past/present) | Non-invasive, but cannot distinguish active from past | | **Stool antigen** | 90–95% | 95–98% | No | Yes | Non-invasive, good for confirmation | | **CLO test (rapid urease)** | 85–95% | 95–98% | Yes | Yes | Rapid (10–15 min), but false-negative if low bacterial load | | **Histology** | 95–98% | 98–100% | Yes | Yes | Gold standard, but requires repeat endoscopy | | **Culture** | 75–90% | 100% | Yes | Yes | Gold standard for sensitivity testing, but slow (4–6 weeks) | **Warning:** Serology (IgG) alone is NOT sufficient here because it cannot distinguish active from past infection. A patient with past H. pylori (now eradicated) would have positive serology but negative UBT. ### Clinical Decision Tree ```mermaid flowchart TD A[Peptic ulcer + negative CLO test]:::outcome --> B{Confirm H. pylori status}:::decision B -->|Non-invasive needed| C[Urea breath test]:::action B -->|Invasive acceptable| D[Repeat endoscopy + biopsy]:::action C --> E{UBT positive?}:::decision E -->|Yes| F[Eradicate H. pylori + stop aspirin]:::action E -->|No| G[Aspirin is culprit → switch antiplatelet]:::action D --> H[Histology + culture]:::action ``` ### Management Implication If UBT is positive: initiate eradication therapy and discontinue aspirin (switch to clopidogrel or another agent if needed). If UBT is negative: the ulcer is aspirin-induced; stop aspirin and use a PPI for 4–8 weeks.