title: Symptom Index or Symptom Association Probability?: A Closer Look at Symptom Association in Suspected GERD Patients.
abstract: BACKGROUND
  Symptom index (SI) and symptom association probability (SAP) are popular methods used to measure symptom association in patients with gastroesophageal reflux disease (GERD).
  
  
  OBJECTIVE
  To investigate whether these 2 methods yield similar results in analysis of both typical and atypical GERD symptoms.
  
  
  METHODS
  Combined impedance-pH reflux studies of 1471 patients tested for possible GERD symptoms from January 2010 to May 2015 were reviewed. SI and SAP were analyzed for typical and atypical GERD symptoms including heartburn, regurgitation, indigestion, chest pain, cough, and throat clearing (TC). Patients who reported <3 symptom events during the 24-hour monitoring period were excluded. ON and OFF proton pump inhibitor (PPI) groups were reviewed. Kappa coefficient (κ) rather than simple percentage was used to measure the agreement rate. Simple percentage agreement is a less reliable method compared with κ.
  
  
  RESULTS
  On PPI therapy, there was a good κ between SI and SAP for regurgitation (0.68) and indigestion (0.64), moderate for heartburn (0.48) and chest pain (0.51), and poor for cough (0.33) and TC (0.29). There was a lower κ OFF PPI therapy for heartburn (0.36), regurgitation (0.44), and indigestion (0.50). But there was no difference in κ for chest pain (0.61), cough (0.29), and TC (0.33).
  
  
  CONCLUSIONS
  SI and SAP showed better agreement for patients with typical GERD symptoms and even better when tested ON PPI. A better symptom association method is needed for patients with atypical GERD symptoms.
authors.affiliation: Department of Gastroenterology and Hepatology.
authors.forename: Mustafa
authors.initials: M
authors.lastname: Abdul-Hussein
authors.affiliation: Medical University of South Carolina, Charleston, SC.
authors.forename: Crystal
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Department of Gastroenterology and Hepatology.
authors.forename: Donald
authors.initials: D
authors.lastname: Castell
mesh_terms: D017097:Electric Impedance; D050782:Esophageal pH Monitoring; D005260:Female; D005764:Gastroesophageal Reflux / Q000175:diagnosis* / Q000188:drug therapy / Q000473:pathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D054328:Proton Pump Inhibitors / Q000627:therapeutic use; D012720:Severity of Illness Index
chemical_list: D054328:Proton Pump Inhibitors