title: Supplementing claims data with outpatient laboratory test results to improve confounding adjustment in effectiveness studies of  lipid-lowering treatments.
abstract: BACKGROUND
  Adjusting for laboratory test results may result in better confounding control when added to administrative claims data in the study of treatment effects. However, missing values can arise through several mechanisms.
  
  
  METHODS
  We studied the relationship between availability of outpatient lab test results, lab values, and patient and system characteristics in a large healthcare database using LDL, HDL, and HbA1c in a cohort of initiators of statins or Vytorin (ezetimibe & simvastatin) as examples.
  
  
  RESULTS
  Among 703,484 patients 68% had at least one lab test performed in the 6 months before treatment. Performing an LDL test was negatively associated with several patient characteristics, including recent hospitalization (OR = 0.32, 95% CI: 0.29-0.34), MI (OR = 0.77, 95% CI: 0.69-0.85), or carotid revascularization (OR = 0.37, 95% CI: 0.25-0.53). Patient demographics, diagnoses, and procedures predicted well who would have a lab test performed (AUC = 0.89 to 0.93). Among those with test results available claims data explained only 14% of variation.
  
  
  CONCLUSIONS
  In a claims database linked with outpatient lab test results, we found that lab tests are performed selectively corresponding to current treatment guidelines. Poor ability to predict lab values and the high proportion of missingness reduces the added value of lab tests for effectiveness research in this setting.
authors.affiliation: Division of Pharmacoepidemiology and Pharmacoeconomics, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02120, USA. schneeweiss@post.harvard.edu
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schneeweiss
authors.forename: Jeremy A
authors.initials: JA
authors.lastname: Rassen
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Glynn
authors.forename: Jessica
authors.initials: J
authors.lastname: Myers
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Daniel
authors.forename: Joseph
authors.initials: J
authors.lastname: Singer
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Solomon
authors.forename: Seoyoung
authors.initials: S
authors.lastname: Kim
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Rothman
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.forename: Jerry
authors.initials: J
authors.lastname: Avorn
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001384:Azetidines / Q000627:therapeutic use*; D003955:Diagnostic Tests, Routine; D004338:Drug Combinations; D000069499:Ezetimibe, Simvastatin Drug Combination; D005260:Female; D006442:Glycated Hemoglobin / Q000187:drug effects; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000627:therapeutic use; D000960:Hypolipidemic Agents; D007345:Insurance Claim Review; D008055:Lipids / Q000097:blood; D008075:Lipoproteins, HDL / Q000097:blood* / Q000187:drug effects; D008077:Lipoproteins, LDL / Q000097:blood* / Q000187:drug effects; D008297:Male; D016345:Medicare Part B; D020398:Medicare Part C; D008875:Middle Aged; D019821:Simvastatin / Q000627:therapeutic use*; D014481:United States; D055815:Young Adult
chemical_list: D001384:Azetidines; D004338:Drug Combinations; D000069499:Ezetimibe, Simvastatin Drug Combination; D006442:Glycated Hemoglobin; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D000960:Hypolipidemic Agents; D008055:Lipids; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D019821:Simvastatin; C517652:hemoglobin A1c protein, human