title: Measurements of 25-hydroxyvitamin D concentrations in archived dried blood spots are reliable and accurately reflect those in plasma.
abstract: BACKGROUND
  Recognition that vitamin D might be associated with many chronic diseases has led to large-scale epidemiological and clinical studies. Dried blood spots (DBS) are a useful resource for these studies. Consequently, accurate, efficient, and inexpensive assays to quantify 25-hydroxyvitamin D (25OHD) in DBS are required.
  
  
  OBJECTIVE
  This study evaluated the validity and reliability of a liquid chromatography-tandem mass spectrometry assay for measuring 25OHD in archived DBS and compared measurements of 25OHD in DBS with those in plasma.
  
  
  METHODS
  Sixty-two participants in the Melbourne Collaborative Cohort Study who had plasma and matching DBS stored since study entry in the early 1990s were randomly selected for a study calibrating 25OHD concentrations in DBS with plasma. As part of a study of vitamin D and mortality, cancer, and diabetes, we also assessed the reliability of measurements from DBS using 500 replicates placed randomly within 31 batches run over 15 months.
  
  
  METHODS
  25OHD concentrations were measured by liquid chromatography-tandem mass spectrometry.
  
  
  RESULTS
  There was good agreement between measurements of 25OHD from DBS and plasma; R(2) = 0.73 from a regression of plasma concentration on DBS concentration. The within-batch and between-batch intraclass correlations from the 500 replicate measurements were 0.82 (95% confidence interval, 0.80, 0.85) and 0.73 (95% confidence interval, 0.68, 0.78), respectively.
  
  
  CONCLUSIONS
  Measuring 25OHD in DBS is a valid and reliable alternative to measuring 25OHD in sera or plasma. A simple calibration model was developed to convert measurements from DBS to equivalent plasma measurements, thus enabling comparisons against clinical reference ranges and with studies using sera or plasma samples.
authors.affiliation: Centre for Epidemiology and Biostatistics (A.K.H., E.J.W., D.R.E.), Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, Victoria 3010, Australia; Cancer Epidemiology Centre (A.K.H., E.J.W., D.R.E.), Cancer Council Victoria, Melbourne, Victoria 3004, Australia; Department of Epidemiology and Preventive Medicine (E.J.W.), Monash University, Melbourne, Victoria 3004, Australia; NorthWest Academic Centre (P.R.E.), The University of Melbourne and Western Health, St Albans, Victoria 3021, Australia; Queensland Brain Institute (D.K., D.W.E.), The University of Queensland, St Lucia, Queensland 4072, Australia; and Queensland Centre for Mental Health Research (D.W.E.), The Park Centre for Mental Health, Wacol, Queensland 4076, Australia.
authors.forename: Alicia K
authors.initials: AK
authors.lastname: Heath
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Williamson
authors.forename: Peter R
authors.initials: PR
authors.lastname: Ebeling
authors.forename: David
authors.initials: D
authors.lastname: Kvaskoff
authors.forename: Darryl W
authors.initials: DW
authors.lastname: Eyles
authors.forename: Dallas R
authors.initials: DR
authors.lastname: English
mesh_terms: D000328:Adult; D000368:Aged; D002138:Calibration; D002853:Chromatography, Liquid / Q000379:methods / Q000592:standards; D003920:Diabetes Mellitus / Q000097:blood / Q000453:epidemiology; D059788:Dried Blood Spot Testing / Q000379:methods* / Q000592:standards*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009369:Neoplasms / Q000097:blood / Q000453:epidemiology; D011237:Predictive Value of Tests; D011446:Prospective Studies; D012016:Reference Values; D015203:Reproducibility of Results; D012307:Risk Factors; D053719:Tandem Mass Spectrometry / Q000379:methods / Q000592:standards; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000032:analysis / Q000097:blood
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D