Several years ago, an “obituary” was written for the pH probe (Putnam PE,J Pediatr. 2010; 157(6):878-80) due to the presumed superiority of pH-impedance (pH-MII) studies in detecting gastroesophageal reflux disease (GERD) As noted in previous blogs (see below), there have remained a number of concerns with the assumption that pH-MII is an improvement over pH studies without impedance. Several recent studies elaborate on those concerns:
- Cheng F-K F, et al. Clin Gastroenterol Hepatol 2015; 13: 867-73
- Patel A, et al. Clin Gastroenterol Hepatol 2015; 13: 884-91
- Vaezi MF. Clin Gastroenterol Hepatol 2015; 13: 892-94 (editorial)
In the first study, the authors identified 221 patients and retrospectively reviewed GERD testing from 2006-2011. Prior to testing, 97% had received prescribed PPIs before testing; however, PPIs were discontinued for at least 1 week prior to evaluation which included upper endoscopy, esophageal manometry, and pH-MII.
- 21 (10%) had erosive esophagitis
- 61 (27%) had nonerosive reflux disease with increased pH
- 18 (8%) had nonerosive reflux disease with abnormal impedance
- 30 (14%) had hypersensitive esophagus
- 18 (8%) had functional heartburn
- 30 (14%) had other functional disorders
- 43 (19%) were undetermined
Thus, this retrospective study showed that the majority (roughly 2/3rds) of patients with GERD symptoms on PPI therapy did not have GERD based on objective testing. The authors chose to test off PPI therapy “because we postulated that the pretest probability of GERD diagnosis was low, primarily given their lack of response to PPI.”
In the second study, 187 subjects (≥18 years) underwent pH-MII testing in a prospective study from 2005-2010. 49.7% were tested off proton pump inhibitor therapy. Abnormal acid exposure time consistently predicted symptomatic outcome. The authors note that performing pH-MII off PPI therapy best predicts response to antireflux therapy
In the third reference, the editorial which commented on the second, there are several useful points:
- “There is little doubt that pH-impedance testing provides a more sensitive means of comprehensively identifying reflux events in a given patient. However, to date, studies have failed to demonstrate that it provides any significant additional clinical benefit.”
- “Caution must be exercised when incorporating the added objective data from non-acidic or weakly acidic reflux events into treatment decision-making…Studies including Patel et al have not shown that knowledge regarding continued non-acid or weakly acid reflux events alter patient outcomes.”
- “Wireless pH testing is generally better tolerated and provides longer measurement duration”
- The use of symptom indices are too subjective. “Recent data question the use of these indices especially in those with refractory symptoms and minimal reflux by pH or impedance testing.” SI and SAP could be altered by chance occurrences….”A colleague expert in esophageal diseases …once said: “I know the tests are no good but I don’t know what else to use.'”
- “Let us simplify our approach on the basis of available data and not use measures that we know are suboptimal at best.”
After looking at these studies and the previous pH probe obituary, I’m reminded of a story. Several religious leaders were asked what they wanted someone to say at their funeral. A few stated that they wanted their congregants/flock to comment on their values, like piety and charity. However, one said, “I hope they say, ‘Look he’s moving!'”
Bottomline: There is no reliable evidence that pH-MII testing improves outcomes over conventional pH probe testing. In fact, the use of pH-MII, by lowering the specificity for GERD, could have a detrimental effect. With either test, holding acid suppression for 1 week (with PPIs) is likely to be helpful in interpreting the results.
Related blog posts:
- Even the Experts Agree: pH-MII is a “Flawed Test” | gutsandgrowth
- Why didn’t patient with documented reflux get better with PPI?
- Gastroesophageal Reflux: I know it when I see it | gutsandgrowth
Disclaimer: These blog posts are for educational purposes only. Specific dosing of medications/diets (along with potential adverse effects) should be confirmed by prescribing physician/nutritionist. This content is not a substitute for medical advice, diagnosis or treatment provided by a qualified healthcare provider. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a condition.