title: Standardizing 25-hydroxyvitamin D values from the Canadian Health Measures Survey.
abstract: BACKGROUND
  The Canadian Health Measures Survey (CHMS) is an ongoing cross-sectional national survey that includes a measure of 25-hydroxyvitamin D [25(OH)D] by immunoassay. For cycles 1 and 2, the collection period occurred approximately every 2 y, with a new sample of ∼5600 individuals.
  
  
  OBJECTIVE
  The goal was to standardize the original 25(OH)D CHMS values in cycles 1 and 2 to the internationally recognized reference measurement procedures (RMPs) developed by the US National Institute for Standards and Technology (NIST) and Ghent University, Belgium.
  
  
  METHODS
  Standardization was accomplished by using a 2-step procedure. First, serum samples corresponding to the original plasma samples were remeasured by using the currently available immunoassay method. Second, 50 serum samples with known 25(OH)D values assigned by the NIST and Ghent reference method laboratories were measured by using the currently available immunoassay method. The mathematical models for each step-i.e., 1) YCurrent = XOriginal and 2) YNIST-Ghent = XCurrent -were estimated by using Deming regression, and the 2 models were solved to obtain a single equation for converting the "original" values to NIST-Ghent RMP values.
  
  
  RESULTS
  After standardization (cycles 1 and 2 combined), the percentage of Canadians with 25(OH)D values <40 nmol/L increased from 16.4% (original) to 19.4% (standardized), and values <50 nmol/L increased from 29.0% (original) to 36.8% (standardized). The 25(OH)D standardized distributions (cycles 1 and 2 analyzed separately) were similar across age and sex groups; slightly higher values were associated with cycle 2 in the young and old. This finding contrasts with the original data, which indicated that cycle 2 values were lower for all age groups.
  
  
  CONCLUSIONS
  The shifts in 25(OH)D distribution brought about by standardization indicate its importance in drawing correct conclusions about potential population deficiencies and insufficiencies and in permitting the comparison of distributions between national surveys.
authors.affiliation: Bureau of Nutritional Sciences, Health Canada, Ottawa, Canada;
authors.forename: Kurtis
authors.initials: K
authors.lastname: Sarafin
authors.affiliation: Department of Public Health Sciences, Loyola University of Chicago Stritch School of Medicine, Chicago, IL;
authors.forename: Ramón
authors.initials: R
authors.lastname: Durazo-Arvizu
authors.affiliation: Department of Health Research and Policy, Stanford University School of Medicine, Palo Alto, CA;
authors.forename: Lu
authors.initials: L
authors.lastname: Tian
authors.affiliation: Biomolecular Measurement Division and.
authors.forename: Karen W
authors.initials: KW
authors.lastname: Phinney
authors.affiliation: Chemical Sciences Division, National Institute of Standards and Technology, Gaithersburg, MD;
authors.forename: Susan
authors.initials: S
authors.lastname: Tai
authors.affiliation: Chemical Sciences Division, National Institute of Standards and Technology, Gaithersburg, MD;
authors.forename: Johanna E
authors.initials: JE
authors.lastname: Camara
authors.affiliation: NIH, Office of Dietary Supplements, Bethesda, MD; and.
authors.forename: Joyce
authors.initials: J
authors.lastname: Merkel
authors.affiliation: Statistics Canada, Ottawa, Canada.
authors.forename: Evan
authors.initials: E
authors.lastname: Green
authors.affiliation: NIH, Office of Dietary Supplements, Bethesda, MD; and.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Sempos
authors.affiliation: Bureau of Nutritional Sciences, Health Canada, Ottawa, Canada; steve.brooks@hc-sc.gc.ca.
authors.forename: Stephen P J
authors.initials: SP
authors.lastname: Brooks
mesh_terms: D015652:25-Hydroxyvitamin D 2 / Q000097:blood*; D000293:Adolescent; D000328:Adult; D000368:Aged; D057205:Automation, Laboratory; D002112:Calcifediol / Q000097:blood*; D002170:Canada; D002648:Child; D003430:Cross-Sectional Studies; D042241:Early Diagnosis; D005260:Female; D006801:Humans; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D015596:Nutrition Assessment; D009749:Nutrition Surveys; D012016:Reference Values; D014808:Vitamin D Deficiency / Q000097:blood / Q000175:diagnosis*; D055815:Young Adult
chemical_list: D015652:25-Hydroxyvitamin D 2; D002112:Calcifediol
keywords: CHMS; adequacy; immunoassay; population survey; standardization; vitamin D