title: Positive predictive value of the diagnosis coding for vitamin B12 deficiency anemia in the Danish National Patient Register.
abstract: OBJECTIVE
  The aim of this validation study was to assess the positive predictive value (PPV) of the International Classification of Diseases, 10th revision (ICD-10) diagnosis of vitamin B12 (cobalamin [Cbl]) deficiency anemia in the Danish National Patient Register (DNPR).
  
  
  METHODS
  We identified all patients above 18 years of age recorded in the DNPR with a diagnosis of Cbl deficiency anemia (ICD-10 code: D51) admitted to two Danish university hospitals and one Danish regional hospital from 2000 through 2009. We assessed the PPV using biochemical parameters on Cbl deficiency with or without anemia as reference standards. These data were obtained from the Laboratory Information Systems Database. Data on prescriptions with Cbl supplementation drugs were obtained from the Aarhus University Prescription Database.
  
  
  RESULTS
  We identified 1089 patients coded with a Cbl deficiency anemia diagnosis in the DNPR. The PPV was 31.5% (95% confidence interval [CI]: 28.8%-34.3%) and 36.8% (95% CI: 34.0%-39.7%) depending on definitions of Cbl deficiency with anemia. When using Cbl deficiency without anemia as a reference standard, the PPV was 51.3% (95% CI: 48.4%-54.3%). The PPV for Cbl supplemented patients was 22.2% (95% CI: 18.0%-26.9%) and for non-Cbl supplemented patients 63.9% (95% CI: 60.5%-67.3%).
  
  
  CONCLUSIONS
  The PPVs of the ICD-10 diagnosis coding for Cbl deficiency anemia were generally low in the DNPR. Therefore, this register should be used with caution to study patients with Cbl deficiency anemia.
authors.affiliation: Department of Clinical Epidemiology, Aarhus University Hospital, Aarhus, Denmark.
authors.forename: Inès
authors.initials: I
authors.lastname: Ben Ghezala
authors.forename: Johan Frederik Berg
authors.initials: JF
authors.lastname: Arendt
authors.forename: Rune
authors.initials: R
authors.lastname: Erichsen
authors.forename: Jihen
authors.initials: J
authors.lastname: Zalfani
authors.forename: Henrik
authors.initials: H
authors.lastname: Gammelager
authors.forename: Trine
authors.initials: T
authors.lastname: Frøslev
authors.forename: Morten
authors.initials: M
authors.lastname: Olsen