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

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