title: Are the currently used reference intervals for creatine kinase (CK) reflecting the general population? The Tromsø Study.
abstract: BACKGROUND
  Laboratory reference intervals are not necessarily reflecting the range in the background population. This study compared creatine kinase (CK) reference intervals calculated from a large sample from a Norwegian population with those elaborated by the Nordic Reference Interval Project (NORIP). It also assessed the pattern of CK-normalization after standardized control analyses.
  
  
  METHODS
  New upper reference limits (URL) CK values were calculated after exclusion of individuals with risk of hyperCKemia and including individuals with incidentally detected hyperCKemia after they had completed a standardized control analysis. After exclusion of 5924 individuals with possible causes of hyperCKemia, CK samples were analyzed in 6904 individuals participating in the 6th survey of The Tromsø Study. URL was defined as the 97.5 percentile.
  
  
  RESULTS
  New URL in women was 207 U/L. In men <50 years it was 395 U/L and in men ≥50 years 340 U/L. In individuals with elevated CK, normalization grade after control analysis was inversely correlated to the CK level (p<0.04).
  
  
  CONCLUSIONS
  URL CK values in women and in men <50 years of age were in accordance with URL CK values given by the NORIP. In men ≥50 years, a higher URL was found and the findings suggest an upward adjustment of URL in this age group.
authors: Department of Neurology and Neurophysiology, The University Hospital of North Norway, Tromsø, Norway. hallvard.lilleng@unn.no
authors: Hallvard
authors: H
authors: Lilleng
authors: Stein Harald
authors: SH
authors: Johnsen
authors: Tom
authors: T
authors: Wilsgaard
authors: Svein Ivar
authors: SI
authors: Bekkelund
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001774:Blood Chemical Analysis / Q000592:standards*; D003402:Creatine Kinase / Q000097:blood*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway; D012016:Reference Values
chemical_list: D003402:Creatine Kinase