In a patient with GERD refractory to standard-dose PPI therapy, which finding on 24-hour ambulatory pH monitoring would indicate inadequate acid suppression?

Explanation

## 24-Hour Ambulatory pH Monitoring in GERD **Key Point:** A normal 24-hour pH study shows pH < 4 for less than 4 hours per day. If pH < 4 for **more than 4 hours per day**, this indicates inadequate acid suppression and suggests PPI-refractory GERD or poor compliance. ### Normal pH Monitoring Parameters | Parameter | Normal Value | Abnormal (Inadequate Suppression) | |-----------|--------------|-----------------------------------| | **Total time pH < 4** | < 4 hours/day (< 4.2%) | > 4 hours/day | | **Upright time pH < 4** | < 3 hours/day | > 3 hours/day | | **Supine time pH < 4** | < 1 hour/day | > 1 hour/day | | **Number of reflux episodes** | < 80/day | > 80/day | | **Duration of longest episode** | < 20 minutes | > 20 minutes | **High-Yield:** In PPI-refractory GERD, a 24-hour pH study helps distinguish true acid reflux (inadequate suppression) from non-acid reflux (bile reflux, mechanical factors). If pH monitoring shows adequate suppression (pH < 4 for < 4 hours), the symptoms are likely due to non-acid reflux, and alternative diagnoses (functional heartburn, achalasia, rumination) should be considered. **Clinical Pearl:** Patients on standard-dose PPI therapy should achieve pH < 4 for only 1–3 hours per day. If monitoring shows > 4 hours at pH < 4, consider dose escalation, twice-daily dosing, or switching to a different PPI before labeling as "refractory."