Ambulatory Esophageal pH Monitoring: Interpretation and Clinical Utility in GERD

What Ambulatory pH Monitoring Measures

This 24–48 hour test (catheter-based or wireless capsule) quantifies gastroesophageal reflux and correlates it with symptoms.

Key Parameters

• Acid Exposure Time (AET): % time esophageal pH <4. Normal <4–5%; >6% diagnostic for GERD (off PPI). On PPI, thresholds differ.
• Total Reflux Episodes: Number of pH drops <4. High count suggests impaired clearance or hypersecretion.
• Symptom Association Probability (SAP) / Symptom Index (SI): Statistical correlation between reflux events and patient-recorded symptoms (heartburn, regurgitation, cough). SAP >95% = positive association.
• Supine vs. Upright AET: Supine reflux indicates impaired nocturnal clearance; guides head-of-bed elevation.
• Postprandial AET: Assesses meal-triggered reflux; informs dietary/timing advice.
• PPI Response Assessment: On-therapy pH monitoring evaluates acid suppression adequacy (target AET <1–2% on PPI).

Clinical Decision-Making

• Confirms GERD when endoscopy negative (NERD).
• Distinguishes refractory GERD from functional heartburn (negative SAP).
• Pre-operative assessment for fundoplication.
• Evaluates extraesophageal symptoms (cough, asthma, laryngitis).

Interpretation requires integration with endoscopy, manometry, and clinical context.