Objective: To explore the diagnostic value and optimal cut-off point of symptom index (SI) in gastroesophageal reflux-induced chronic cough (GERC).
Methods: The recordings of multichannel intraluminal esophageal impedance and pH monitoring were retrospectively analyzed in 118 patients with suspicious GERC. SI for all the refluxes, acid reflux and non-acid reflux was calculated respectively by analyzing the temporal association between detected reflux and cough recorded on diary card. Based on the favorable response to the anti-reflux therapy, the diagnostic value for GERC of SI was evaluated and compared with that of the symptom association probability (SAP).
Results: GERC was definitely determined in 100 patients (84.7%). When SI for all the refluxes was used for the diagnosis of GERC, the cut-off point of ≥ 45% had the highest diagnostic efficacy, with the sensitivity of 56.0%, the specificity of 83.3% and Youden index of 0.393. SI for acid or non-acid reflux had the same optimal cut-off point of ≥ 30% and presented with the similar efficacy in the diagnosis of acid or non-acid GERC. Compared with SAP of ≥ 75%, SI for all the refluxes of ≥ 45% had a lower sensitivity (56.0% vs 75.0%, χ(2) = 7.988, P = 0.005), a higher specificity (83.3% vs 44.4%, χ(2) = 5.900, P = 0.015) and the comparable positive or negative predictive value in the diagnosis of GERC. The diagnostic accuracy for GERC was further improved when combining SI for all the refluxes with SAP.
Conclusion: SI for all the refluxes has a diagnostic value similar to SAP and its optimal cut-off point for GERC may be ≥ 45%.