title: The Copenhagen Primary Care Differential Count (CopDiff) database.
abstract: BACKGROUND
  The differential blood cell count provides valuable information about a person's state of health. Together with a variety of biochemical variables, these analyses describe important physiological and pathophysiological relations. There is a need for research databases to explore associations between these parameters, concurrent comorbidities, and future disease outcomes.
  
  
  RESULTS
  The Copenhagen General Practitioners' Laboratory is the only laboratory serving general practitioners in the Copenhagen area, covering approximately 1.2 million inhabitants. The Copenhagen General Practitioners' Laboratory has registered all analytical results since July 1, 2000. The Copenhagen Primary Care Differential Count database contains all differential blood cell count results (n=1,308,022) from July 1, 2000 to January 25, 2010 requested by general practitioners, along with results from analysis of various other blood components. This data set is merged with detailed data at a person level from The Danish Cancer Registry, The Danish National Patient Register, The Danish Civil Registration System, and The Danish Register of Causes of Death.
  
  
  CONCLUSIONS
  This paper reviews methodological issues behind the construction of the Copenhagen Primary Care Differential Count database as well as the distribution of characteristics of the population it covers and the variables that are recorded. Finally, it gives examples of its use as an inspiration to peers for collaboration.
authors: The Research Unit for General Practice and Section of General Practice, Department of Public Health, University of Copenhagen, Copenhagen, Denmark ; Department of Hematology, Roskilde University Hospital, Copenhagen, Denmark.
authors: Christen Lykkegaard
authors: CL
authors: Andersen
authors: The Research Unit for General Practice and Section of General Practice, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors: Volkert Dirk
authors: VD
authors: Siersma
authors: The Research Unit for General Practice and Section of General Practice, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors: Willy
authors: W
authors: Karlslund
authors: Department of Hematology, Roskilde University Hospital, Copenhagen, Denmark.
authors: Hans Carl
authors: HC
authors: Hasselbalch
authors: The Elective Laboratory of the Capital Region, Copenhagen University Hospital, Copenhagen, Denmark.
authors: Peter
authors: P
authors: Felding
authors: Department of Hematology, Copenhagen University Hospital, Copenhagen, Denmark.
authors: Ole Weis
authors: OW
authors: Bjerrum
authors: The Research Unit for General Practice and Section of General Practice, Department of Public Health, University of Copenhagen, Copenhagen, Denmark.
authors: Niels
authors: N
authors: de Fine Olivarius
keywords: differential leukocyte count; nationwide health registers; research