Gastroesophageal reflux (GER) is defined as the physiological, involuntary, and asymptomatic passage of gastric contents into the esophagus.1,2 When a condition is developed where gastroesophageal reflux causes troublesome symptoms such as heartburn, crying, irritability, sleep disturbance, cough, or complications (pneumonia, imminent risk of life, laryngitis, otitis), it is considered gastroesophageal reflux disease (GERD).3–5

Strategies to document the diagnosis of GERD are complex because several types of instruments and tests can be used. The barium swallow X-ray test, scintigraphy, and abdominal ultrasonography can be considered complementary exams.5 Upper gastrointestinal endoscopy (UGE) conducted with or without esophageal, stomach, or duodenum biopsy and manometry make it possible to analyze GERD complications.1–5 Moreover, the pHmetry defines the episodes of acid GER and their relation to the symptoms.4

However, it is necessary to use these instruments in a complementary and/or associated way, since individually they are useful to assess anatomy, motility, symptomatology, or possible complications. Currently, multichannel intraluminal impedance-pH (MIIpH) is considered the gold standard test for the direct diagnosis of GERD.4–6

MIIpH can determine if esophageal content is present and its flow (retrograde or anterograde), by analyzing variation of the electrical conductance (checked by multiple sensors) and simultaneously monitoring intraesophageal pH.4,5 It can also verify physical properties of the bolus: fluid, gaseous, or mixed; the relation of the bolus movement with the prandial period and with the symptoms, also making it possible to identify acid and non-acidic events, in association with the intraesophageal pH.4–6 The efficacy of MIIpH regarding GERD diagnosis has been investigated, discussed, and recently diffused in clinical practice.5,7

Safety and efficacy confirmation of this test allows its indication and choice by health professionals, aiming a better cost-benefit relation and adjustments of the resources available in diagnostic centers.7–10 One of the strategies used for quality verification is the evaluation of the psychometric properties (PP) and their outcome variables.

PP have demonstrated to be important for the assessment of tests used to diagnose diseases.11–13 Among the variables analyzed regarding PP, there are the following: reliability, internal consistency, validity, responsiveness, reproducibility, and viability.14 Such variables aim to avoid compromising the reliability of the tests and to make more adequate and organized measurements possible, determining well-established criteria for health professionals to be able to select the most accurate test.

The present review aimed to systematically verify studies that analyzed the PP of MIIpH for the diagnosis of GER in children and adolescents.

The investigation regarding diagnosis of GERD continues to be the subject of numerous recent studies, as well as the use of different tools for this purpose.1–5,7

The PP are as follows: verification of internal consistency, validity, reproducibility, responsiveness, feasibility, sensitivity, and specificity.12,14,25–27 However, the concern with applicability in a safe, reliable, and standardized way is seldom discussed in the literature.

Findings of the present systematic search state that the PP are still not presented in a clear way and are not included in most of the studies related to the diagnosis through specific instruments. The statements about GER and GERD demonstrate different situations and questions. Among them is the use of diagnostic instruments such as pHmetry, which despite having been considered a gold standard for a long time, can only evaluate episodes of acid reflux and does not assess immediate postprandial GER or characterize the physicochemical properties of GER, not allowing an accurate swallowing investigation.6,7,9,28

As a more complete alternative to evaluate the different aspects of GERD, the MIIpH is an examination based on the association of pHmetry and the evaluation of electric potential of esophageal contents by multiple channels, which allows characterizing acid and non-acidic episodes, in addition to assessing retrograde or anterograde “bolus” flow, physical-chemical properties, and association to symptoms.4,5,28,29

As previously mentioned, the evaluation of the PP of a diagnostic test is useful in order to assure the quality of its application.12,14 The search for PP was performed with the objective of obtaining safety in the use of the MIIpH with more judicious, organized, and better-elucidated parameters.

In the analyzed articles the PP of sensitivity was recorded, which is the probability of a test identifying among sick individuals who actually has the disease16,18,20–23,30; specificity, which represents the ability of a test to identify among the normal individuals those who do not really have the disease18,20,22,23,30; accuracy, which refers to the degree to which the test is able to determine the true value of what is being measured19,30; and, finally, reproducibility, which has the purpose of verifying the consistency of results when the exam is repeated.17,30

The PP most used in the studies were sensitivity and specificity, as shown in Blasco-Alonso et al.20; Kızılkan et al.,22 and Abdallah et al.23 These properties were used to compare MIIpH with other diagnostic instruments regarding GERD, such as bronchoalveolar lavage (BAL),23 GER scintigraphy (GES),22 and pHmetry,20 in which sensitivity values of around 77% to 100% and specificity varying from 23.1% to 80% for MIIpH were found.20,22 The authors concluded that MIIpH alone is a very sensitive and very specific method for the diagnosis of GERD and its complications.

In cases of atypical GERD symptoms, in which respiratory manifestation was the only or most important event, MIIpH also showed high sensitivity for the diagnosis of GERD, as can be observed in the results obtained by Abdallah et al. (77%),23 Lau et al. (73.0%),21 and Blasco-Alonso et al. (100%).20

Sensitivity alone was evaluated in the studies of Lau et al.21 and Rosen et al.16 In both studies, most of the sample analysis was retrospective and MIIpH was compared with pHmetry. Sensitivity values of MIIpH ranged from 73% to 80.3%, which demonstrated better sensitivity of the MIIpH regarding diagnosis of GERD in children.

These high sensitivity and safety values of MIIpH regarding diagnosis of GERD in children were also found by other authors. Safe et al.31 reviewed all MIIpH tests over a six-year period at Sydney Children's Hospital and found that the use of MIIpH resulted in 50.4% higher diagnoses of GERD in comparison to the isolated pHmetry, regardless of the use of antireflux medications. Moreover, the sensitivity value for diagnosis of children who were taking medication was 92.94%.

Wenzel, in 2003,32 presented a retrospective study that simultaneously analyzed the MIIpH, isolated pHmetry, and polysomnography tests in 22 infants and children who had apnea, aspiration, and respiratory disorders. The author concluded that the pHmetry associated with impedancemetry proved to be a valuable tool to diagnose GERD regardless of its pH value and association of GER with symptoms, as well as the possibility of evaluating the composition of the refluxate, and its movement, duration, and esophageal clearance. In 2014 Mousa et al.29 published an analysis of MIIpH tracings in 117 children with GER with normal levels of acid and no association of GER episodes with symptoms. The authors concluded that these values can be used as comparison references to identify infants and/or children who may be at risk of developing clinical manifestations associated with GERD due to abnormal GERD patterns.

More specifically, in the work of Rosen et al. in 2006,16 two procedures were carried out. Initially, a prospective study where MIIpH was performed in infants and children who discontinued antacid medication 48h previously to the test, to assess sensitivity of pHmetry and MIIpH. This practice is common in the application routine of the MIIpH29 and they observed that the sensitivity was similar, approximately 80%, in the two tests: (pHmetry=80.6%±18.2% and MIIpH=76.1%±13.5%). In the sequence, they performed a retrospective evaluation of MIIpH exams with the same age group and the group who used medication: proton pump inhibitor, H2 blocker, or both. The sensitivity of MIIpH remained constant while pHmetry fell to approximately 40% (pHmetry=47.2%±36.0% and MIIpH=80.3%±21.1%). This decrease in the sensitivity of pHmetry may be related to the diet, which in this age group, is predominantly of milk and consequently low acidic.

Another psychometric property found in publications was the accuracy of MIIpH in relation to isolated pHmetry in one group of infants (<12months) and another group of children (>12months).19 The findings showed that the mean accuracy for both groups was higher for MIIpH, considering that it was 86% (83–90% CI) for the total number of refluxes and 79% (74–84%) for the total number of acid refluxes, which, according to the authors, demonstrated that MIIpH is a powerful tool for GERD assessment.19

Regarding the reproducibility variable, the prospective study of Dalby et al. in 200717 was the only one that conducted the monitoring in two periods of 24 consecutive hours. The evaluation consisted of verifying all episodes of GER, acid and non-acid GER, and intra- and interobserver variability in order to analyze the results. The lower and upper limit values of approval (LOA) for these parameters made it possible to conclude that the simultaneous evaluation of MIIpH and pHmetry is a very reliable technique in children and infants. Moreover, the smaller variability among the results is due to the use of MIIpH.

In the present review some parameters related to psychometric properties were verified; however, only sensitivity and specificity were reported. Moreover, accuracy and reproducibility were each mentioned in one article. No studies were found regarding results of the response to treatment using MIIpH.

Although the studies included in this review present individuals with ages ranging from birth to 18 years, the analyses in some studies were carried out in different age groups. In pediatrics, no studies have been validated in healthy children in all different age groups.

In the final analysis, it was pointed out that the sensitivity variable was the most commonly used in all analyzed articles, being able to express and guarantee the importance of MIIpH in the diagnosis of GERD in infants and children. Sensitivity is more related to characteristics of the assessment instrument structure and represents an important issue to be investigated in longitudinal studies,12 since it reflects the ability to truly identify the disease among sick individuals.

Regarding the assessment of the methodological quality of the studies, low risk of bias was observed in all domains, above 50%, reaching 100% low risk for the “Index Test” and “Reference Standard” domains. There was concern about applicability of 100% regarding the “Index test” domain.

The evaluation of PP in studies that used instruments for diagnosing GERD showed that the interest in this context is still undervalued. Since few studies have verified these PP, some questions about clinical applicability still remain. In this review, it was verified that MIIpH is a safe and effective tool, and presents higher sensitivity values than the pHmetry regarding the diagnosis of GERD.

The authors declare no conflicts of interest.