title: Benchmarking by HbA1c in a national diabetes quality register--does measurement bias matter?
abstract: BACKGROUND
  Bias in HbA1c measurement could give a wrong impression of the standard of care when benchmarking diabetes care. The aim of this study was to evaluate how measurement bias in HbA1c results may influence the benchmarking process performed by a national diabetes register.
  
  
  METHODS
  Using data from 2012 from the Norwegian Diabetes Register for Adults, we included HbA1c results from 3584 patients with type 1 diabetes attending 13 hospital clinics, and 1366 patients with type 2 diabetes attending 18 GP offices. Correction factors for HbA1c were obtained by comparing the results of the hospital laboratories'/GP offices' external quality assurance scheme with the target value from a reference method.
  
  
  RESULTS
  Compared with the uncorrected yearly median HbA1c values for hospital clinics and GP offices, EQA corrected HbA1c values were within ±0.2% (2 mmol/mol) for all but one hospital clinic whose value was reduced by 0.4% (4 mmol/mol). Three hospital clinics reduced the proportion of patients with poor glycemic control, one by 9% and two by 4%.
  
  
  CONCLUSIONS
  For most participants in our study, correcting for measurement bias had little effect on the yearly median HbA1c value or the percentage of patients achieving glycemic goals. However, at three hospital clinics correcting for measurement bias had an important effect on HbA1c benchmarking results especially with regard to percentages of patients achieving glycemic targets. The analytical quality of HbA1c should be taken into account when comparing benchmarking results.
authors.forename: Siri
authors.initials: S
authors.lastname: Carlsen
authors.forename: Geir
authors.initials: G
authors.lastname: Thue
authors.forename: John Graham
authors.initials: JG
authors.lastname: Cooper
authors.forename: Thomas
authors.initials: T
authors.lastname: Røraas
authors.forename: Lasse Gunnar
authors.initials: LG
authors.lastname: Gøransson
authors.forename: Karianne
authors.initials: K
authors.lastname: Løvaas
authors.forename: Sverre
authors.initials: S
authors.lastname: Sandberg
mesh_terms: D000328:Adult; D019985:Benchmarking; D015982:Bias; D001774:Blood Chemical Analysis / Q000706:statistics & numerical data*; D003922:Diabetes Mellitus, Type 1 / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D058005:General Practitioners / Q000706:statistics & numerical data; D006442:Glycated Hemoglobin / Q000032:analysis*; D006801:Humans; D011786:Quality Control; D012042:Registries
chemical_list: D006442:Glycated Hemoglobin