How helpful is a pH-Impedance Study in Identifying Reflux-Induced Symptoms?

In both kids and adults, individuals presenting with complaints of reflux more often have other problems like functional heartburn or reflux hypersensitivity (see posts below).  A recent prospective, cross-sectional study (LB Mahoney et al. JPGN 2020; 70: 31-36) provides data that further shows that abnormal pH-impedance (pH-MII) testing does NOT predict reduced quality of life (QOL) in children with reflux symptoms (n=82).

Key findings:

  • 38% had abnormal pH-MII testing; however, there were no significant differences in QOL scores on any of the tested questionairres between those with normal or abnormal pH-MII studies.
  • Subjects with gross esophagitis on EGD reported significantly worse QOL scores. Microscopic esophagitis was not associate with differences in QOL scores.

The implication of this study is that reflux without esophagitis is NOT a driver of abnormal QOL parameters; instead, functional GI disorders are likely more important.

My take: This study makes it clear that gross endoscopic findings are much more consequential than abnormal pH-MII studies.

Related blog posts:

Linking Reflux and Tooth Erosion

Every now and then a dentist sends a kid to our GI practice due to eroded teeth because of concerns about reflux damaging the enamel.  While it is recognized that reflux may damage teeth, the exact frequency is unclear.  Other questions:

  • Which asymptomatic kids with poor dentition require GI evaluation?
  • What is the best way to evaluate these children?
  • If reflux is identified, how long should they remain on treatment? Forever?
  • How effective is reflux treatment in reducing tooth damage?

While none of these questions have been definitely answered, Rosen et al (JPGN 2016; 62: 309-13) show that acid reflux rather than nonacid reflux is predictive of tooth erosion. In this study, the authors used a prospective cohort of 27 children (age ≥3 years)–ALL of them were ON acid suppression (for >1 year) at the time of pH-MII testing.  Key findings:

  • Prevalence of tooth erosion was 10 or 27 (37%)
  • There was correlation with acid reflux episodes (& time in reflux) and tooth erosion, r=0.44, P=0.02
  • There was correlation with reflux index as well, r=0.54, P=0.004,  In the tooth erosion group, the mean reflux index was 7.3% compared with 1.6% in no dental erosion group.
  • There was no correlation with nonacid reflux with tooth erosion

The authors’ discussion highlights many prior relevant studies and indicates that a pH-metry study alone (rather than pH-MII) “may be adequate.” They note some of the limitations of this study which included a small number of patients and potential referral bias, as these children had suspected GERD.  In the methods section, the authors state that their standard practice, at the time of the study, was to maintain patients on prior acid suppression medication.  It would be useful to acknowledge that many experts, at this time, recommend doing pH-MII studies as well as standard pH studies off all acid suppression due to improved sensitivity/accuracy.

My take: This study shows that in the 10 children with tooth erosion who had suspected GERD, there was correlation with acid reflux but not with nonacid reflux.

Related blog post: Notes from PPI Webinar GutsandGrowth

Unrelated but interesting: Are medical errors really the 3rd leading cause of death in U.S.? Here’s NPR’s summary of a recent BMJ article which makes that claim: Only Heart Disease and Cancer Exceed Medical Errors As Cause of U.S. Death

Gibbs Gardens

Gibbs Gardens


Selective Data Mining: Reflux and Bronchopulmonary Dysplasia

With some studies, the abstract may suggest a more compelling result than is truly evident.  That’s how I feel about a recent report (Nobile S, et al. J Pediatr 2015; 167: 279-85).

Here’s the conclusion (verbatim) from the abstract: “The increased number of (and sensitivity for) pH-only events among infants with BPD may be explained by several factors, including lower milk intake, impaired esophageal motility, and a peculiar autonomic nervous system response pattern.”

To me, it sounds like this prospective study of pH-multichannel intraluminal impedance (pH-MII) of 46 infants born ≤32 weeks gestation (12 with bronchopulmonary dysplasia (BPD) and 34 without BPD) must have identified something important linking gastroesophageal reflux disease (GERD) and BPD.  But, the real findings, in my view, are that this is a negative study. Period.

Here are the results reported in the abstract:

  • “Infants with BPD…had increased numbers of pH-only events (median number 21 v 9) and a higher symptom symptom sensitivity index for pH-only events (9% vs. 4.9%)”
  • They also state: “the number and characteristics of acid, weakly acid, nonacid and gas gastroesophageal reflux events, acid exposure, esophageal clearance, and recorded symptoms did not significantly differ between the 2 groups.”

Here’s a little more data –not in the abstract:

  • The P value for the difference in pH-only events was .360
  • The authors could just have easily pointed out (in the abstract) that infants without BPD had increased acid exposure: 40.5 min compared with 27.0 min (P = .599)

What should have been in the abstract conclusion? Perhaps, the first line of their discussion: “Infants with BPD did not have significantly higher GER features compared with infants without BPD as measured by esophageal pH-MII monitoring, except for higher occurrence of pH-only events and higher SSI for pH-only events.”

The authors try to explain the differences in the BPD patients by highlighting some of the potential mechanisms of reflux and/or autonomic dysfunction.  I think the limitations of this study deserve careful scrutiny.  This was a small study with only 12 BPD infants.  There was a significant selection bias -only ‘symptomatic’ infants were included.  Some of the factors affecting BPD directly could have an indirect effect on reflux (eg. caffeine).

The authors make one other point: “we believe pharmacologic treatment for GER should be initiated only after the demonstration of pathologic pH-MII monitoring to avoid unnecessary drug therapy, adverse events, and costs.”

Related blog posts:

Grand Prismatic Spring, Yellowstone

Grand Prismatic Spring, Yellowstone

Even the Experts Agree: pH-MII is a “Flawed Test”

A recent study (JPGN 2014; 58: 22-26) reports on the combination of a new technique of intraesophageal pressure recording (IEPR) along with multichannel intraluminal impedance with pH (pH-MII).  While this prospective study is small with only 20 children who had a history of chronic intractable cough, some of its observations are important, especially for those who have embraced pH-MII.

In determining whether the pH-MII studies were abnormal the authors relied on symptom index (SI) defined as the number of symptoms associated with reflux/total number of symptoms.  SI is considered positive if >50%.  In addition, the authors calculated the symptoms sensitivity index (SSI) which is defined as the total number of reflux episodes associated with symptoms/total number of reflux episodes; it is considered positive if it is >10%.  The authors note SAP and SI have a comparable positive predictive value and “our experience suggests that SAP calculation using software is unreliable.”

Key Results/Discussion:

  • IEPR changed the diagnosis in 15-20% of patients depending of scoring index used.  That is, IEPR assisted the detection of reflux-associated cough.
  • IEPR detected 106% more coughs than patient report alone.  Thus, this study, if accurate, indicates that “symptom reporting during pH or pH-MII testing is significantly flawed and, if possible, should not be used alone for clinical decision making.”
  • “We did not find a significant association between cough production and the height of the refluxate.”
  • The authors argue that since nonacid reflux can be associated with cough and is not always detected with pH-MII, that this could “explain why studies that have tried to use pH criteria to predict clinical outcome after acid suppression therapy have been negative.”  The two studies cited at that point by the authors were landmark studies (referenced below) showing that proton pump inhibitors are not effective in children or adults in improving asthma.  I think the authors’ comment misses the importance of these studies entirely.  There are no proven effective GERD (acid or nonacid) therapies that alter the course of asthma.

Take-home message from authors: “Studies are now needed to determine whether this increased detection improves therapeutic outcomes, but clearly, relying on symptom reporting by patients is flawed and clinical decision making based on patient report alone should be done with caution.”

Referenced studies:

  • JAMA 2012; 307: 373-81
  • NEJM 2009; 360: 1487-99

Related blog posts:

Gastroesophageal Reflux: I know it when I see it

      According to Wikipedia, Justice Potter Stewart, in Jacobellis v. Ohio 378 U.S. 184 (1964) stated the following: I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description [“hard-core pornography”]; and perhaps I could never succeed in intelligibly doing so. But I know it when I see it, and the motion picture involved in this case is not that. [Emphasis added.]
     To some extent, ‘I know it when I see it’ has been the mantra about identifying gastroesophageal reflux for advocates for pH-impedance (pH-MII).  Enthusiasts have claimed that pH-MII is vastly superior to pH studies alone for many reasons including the ability to detect more GER episodes than conventional pH studies.  Yet, a major flaw has been a paucity of normative data.  To determine whether there is interobserver and intraobserver agreement in the interpretation of pH-MII, seven expert world groups collaborated on a study to analyze ten pediatric 24-hour tracings (J Pediatr 2012; 160: 441-6).
     Five of these studies were considered easy and five were more challenging due to less obvious features like low baselines, retrograde patterns during swallowing, and moving/crying artifacts.   Among 1242 liquid and mixed GER events, 490 (42%) were scored by the majority of observers.  The authors claim that this is “moderate agreement.”  The automated analysis (AA), not surprisingly, had much better agreement than manual analysis.   With AA there was 94% sensitivity rate and 74% specificity. When looking at AA alone, AA missed 6.5% of events scored by observer consensus and  30% of GER episodes recorded with AA were not detected by majority consensus.
     When looking at each pH-MII recording (Figure 2), there was poor agreement on whether the study was pathologic.  Only five of the studies had uniform agreement that the number of episodes (>73 GER episodes) were either pathologic or not. Those with agreement were all negative studies.  The authors conclude, though, that there was “substantial” agreement based on a mean kappa value of 0.70.
     A comparison to a previous pH-MII publication (Scand J Gastro 2011; 46: 271-6) notes that in this previous study, 83% of pH-MII recordings had a concordant symptom association probability despite underdetection of GER episodes with AA; it was recommended to use ‘AA when the symptom association was positive.  If symptom association was negative, they suggested manual analysis.’
    The conclusions from the current study:
  • ‘In theory, AA is favored over manual analysis due to reproducibility’
  • AA does not seem specific enough to ensure correct marking of GER episodes in infants and children yet
  • Consensus to refine AA needs to be reached …to retain confidence …in impedance

If this is the best that worldwide experts can do with this widespread technology, what does that mean for clinicians in practice?

Additional references:

Recent related posts:

The Medical Pendulum and Gastroesophageal Reflux

Unexplained chest pain

  • -Journal of Gastroenterology and Hepatology 2010;25:817-22. Has some normative pH-MII data.  ‘Can acid (pH) refluxes predict multichannel intraluminal impedance refluxes? A correlation study.’
  • -JPGN 2010; 50: 25. Reflux detected by Impedance does NOT determine fundoplication outcome. n=34.
  • -JPGN 2010; 52: 129. Review. No normative data. Using SAP>95% to correlate symptoms (better than SI or SSI). Main use is to study intractable pts to establish if nonacid reflux is contributing to symptoms.
  • -J Pediatr 2010; 157: 878 (“death of pH probe”), 949. Use of impedance in children. n=225. (70 were discarded). Notes lack of therapeutic possibilities for non-acid reflux.  Symptom index is + if >50%, SAP if >95%. Symptom index is number of symptoms with reflux episode divided by total number of symptom occurrences. SAP, symptom association probability, is a statistical tool that uses 2-minute windows throughout recording to correlate symptom and reflux event.  pH probe 2nd metal for infant -place 2cm above LES.  pH probe 3rd metal for child -place 3cm above LES
  • -Clin Gastro & Hep 2009; 7: 743. n=39 adults. Non-acid reflux events in patients on therapy correlated with acid reflux parameters when patients studied off therapy. Abnormal impedance parameters: total number of reflux events >63 (avg normal was 28). This study relied on # of reflux events more than SAP or SI. SAP or SI is problematic in patients who lack clinical response to PPIs.
  • -Gastroenterology 2009; 136 (suppl 1): S1896. n=143. #of events (not SI or SAP) is then most conservative estimate as well as the one with the highest likelihood of encompassing other symptom assoication parameters.
  • -J Pediatr 2009; 154: 248. n=50. a high # with normal pH had symptom correlation w GER events. (initial cohort was 80 –30 excluded due to problems with study or insufficient symptoms) SAP is superior for correlating symptoms.
  • -Clin Gastro & Hep 2008; 6: 840. Impedance is best tool -D Castell.; -Clin Gastro & Hep 2008; 6: 880.
  • -Clin Gastro & Hep 2008; 6: 482, 521. ‘Impedance/pH is best tool’. Pts who respond to PPIs likely due so due to its effect on chemostimulation; those who continue with symptoms may do so based on mechanostimulation -related to volumes in esophagus not due to acidity.
  • -J Pediatr 2006; 149: 216. Equal frequency of acid and non-acid reflux in 24 pts with asthma. No correlation identified with resp symptoms.
  • -Clin Gastro & Hep 2006; 4: 167. Impedance does not add to pH probe in UNTREATED patients.
  • -JPGN 2002; 34: 511, 519.
  • -Pediatrics 2006; 118: e299, 793. Impedance data in preterm infants. Asymptomatic and affected infants with similar impedance values and both have reflux to upper esophagus.