title: Completeness of prescription information in US commercial claims databases.
abstract: OBJECTIVE
  Pharmacy commercial claims databases are widely used for pharmacoepidemiologic research. However, concerns have been raised that these databases may not fully capture claims for generic medications as a result of patients filling outside the context of their insurance. This has implications for many research activities and quality improvement programs. We sought to estimate the percentage of missing prescriptions in US commercial claims data using a novel design.
  
  
  METHODS
  Using a large US commercial insurance database, we examined the completeness of warfarin prescription claims among patients with atrial fibrillation receiving regular medical follow-up and testing to manage warfarin dosing. We examined 14 different 6-month cross sections. Each cross section was treated independently to identify patients with at least two outpatient diagnoses of atrial fibrillation, two international normalized ratio tests, and one pharmacy claim. Trends in the percentage of patients with prescription claims for generic and branded warfarin were compared by year and 6-month periods using chi-square tests and generalized linear models adjusting for patient characteristics.
  
  
  RESULTS
  Out of 111 170 patients, the percentage of patients with any warfarin drug decreased slightly from 91.7% (95% CI: 91.0, 92.4) in early 2003 to 87.1% (95% CI: 86.7-87.6) in late 2009 (χ(2)  = 93.8, p < 0.0001). Over the same interval, the proportion of patients with generic warfarin exposure appearing increased significantly, whereas the proportion of patients with branded warfarin exposure decreased significantly.
  
  
  CONCLUSIONS
  Our study supports the possibility that some prescriptions may not be captured in US commercial insurance databases.
authors.affiliation: Division of Pharmaceutical Outcomes and Policy, UNC Eshelman School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA.
authors.forename: Julie C
authors.initials: JC
authors.lastname: Lauffenburger
authors.forename: Akhila
authors.initials: A
authors.lastname: Balasubramanian
authors.forename: Joel F
authors.initials: JF
authors.lastname: Farley
authors.forename: Cathy W
authors.initials: CW
authors.lastname: Critchlow
authors.forename: Cynthia D
authors.initials: CD
authors.lastname: O'Malley
authors.forename: Mary T
authors.initials: MT
authors.lastname: Roth
authors.forename: Virginia
authors.initials: V
authors.lastname: Pate
authors.forename: M Alan
authors.initials: MA
authors.lastname: Brookhart
mesh_terms: D000925:Anticoagulants / Q000008:administration & dosage / Q000627:therapeutic use; D001281:Atrial Fibrillation / Q000188:drug therapy; D016009:Chi-Square Distribution; D003430:Cross-Sectional Studies; D016208:Databases, Factual / Q000592:standards / Q000706:statistics & numerical data*; D016903:Drug Monitoring / Q000379:methods; D016568:Drugs, Generic / Q000008:administration & dosage / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D007356:Insurance, Pharmaceutical Services / Q000706:statistics & numerical data; D019934:International Normalized Ratio; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D017891:Pharmacoepidemiology / Q000379:methods*; D055553:Prescription Drugs / Q000008:administration & dosage / Q000627:therapeutic use; D014481:United States; D014859:Warfarin / Q000008:administration & dosage / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D016568:Drugs, Generic; D055553:Prescription Drugs; D014859:Warfarin
keywords: claims data; data quality; generic drugs; pharmacoepidemiology