Acid perfusion test: does it have a role in the assessment of non cardiac chest pain?

Using 24 hour pH monitoring as a reference standard, the usefulness of the acid perfusion (AP) test in predicting gastro-oesophageal reflux disease (GORD) was assessed in 71 non-cardiac chest pain (NCCP) patients and 23 endoscopic oesophagitis patients. Of the 71 NCCP patients, 35 had a positive AP test (of whom 20 had an abnormal 24 hour pH) and 36 had a negative AP test (of whom 14 had an abnormal 24 hour pH study). Thus, the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of the AP test in this group was 59%, 59%, 57%, and 61%, respectively. The corresponding values in the oesophagitis group were 85%, 67%, 94%, and 40%. In the NCCP group when heartburn alone was used as the positive criterion the PPV rose to 74%. When chest pain with or without heartburn was used, however, the PPV dropped to 38%. A 'symptom index' was used to define the number of chest pain episodes that were caused by acid reflux. Only 48% of AP test positive patients had demonstrable acid mediated chest pain. In the NCCP population with a normal oesophageal examination (1) AP test reproduction of chest pain is poorly predictive of GORD; (2) AP test reproduction of heartburn is more predictive of GORD but does not ensure that the chest pain is caused by GORD; (3) a negative AP test does not exclude GORD and (4) only 48% of AP test positive patients have demonstrable acid mediated chest pain. The ambulatory 24 hour pH test may have rendered the AP test obsolete in the assessment of GORD as the cause of NCCP.