Harmonization Study Between LC-MS/MS and Diasorin RIA for Measurement of 25-Hydroxyvitamin D Concentrations in a Large Population Survey.
BACKGROUND
Population-based research on vitamin D has increased dramatically in recent years. Such studies are typically reliant on assay procedures to measure reliable and comparable levels of 25-hydroxyvitamin D [25(OH)D] concentrations.


METHODS
Concentrations of 25(OH)D3and 25(OH)D2were measured using LC-MS/MS in 5,915 participants (aged 31 years) of Northern Finland Birth Cohort 1966. Blood samples were assayed in batches over a course of 18 months. As anomalies were present in the measurements, 200 samples were reassayed using Diasorin RIA. Agreement between measurements was assessed by Passing-Bablok regression and limits of agreement (LoA). To harmonize LC-MS/MS with Diasorin RIA measurements, formulae were derived from the LoA.


RESULTS
Concentrations measured by LC-MS/MS were much higher than those measured by Diasorin RIA, with a mean difference of 12.9 ng/ml. Constant variation was evident between batch measurements after log transformation. Statistical formula was applied separately for each batch of LC-MS/MS measurements, enabling us to remove both the constant and proportional bias that was evident prior to the transformation.


CONCLUSIONS
Despite the introduction of schemes/programs to improve accuracy of assays to measure 25(OH)D, significant differences can still happen. In these instances, methods to harmonize measurements based on a relatively small number of replicates can be successfully applied to establish confidence and to enable between-study comparisons.
Population, Policy and Practice, UCL Institute of Child Health, London, UK.
Diane J
DJ
Berry
Department of Clinical Biochemistry, Royal Liverpool University Hospital, Liverpool, UK.
John
J
Dutton
Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich, UK.
William D
WD
Fraser
Department of Epidemiology and Biostatistics, MRC Health Protection Agency (HPA) Centre for Environment and Health, School of Public Health, Imperial College London, London, UK.|Unit of Primary Care, Oulu University Hospital, Oulu, Finland.|Department of Children, Young People and Families, National Institute for Health and Welfare, Oulu, Finland.|Biocenter Oulu, Institute of Health Sciences, University of Oulu, Oulu, Finland.
Marjo-Riitta
MR
Järvelin
Population, Policy and Practice, UCL Institute of Child Health, London, UK.|Centre for Population Health Research, School of Health Sciences and Sansom Institute of Health Research, University of South Australia, Adelaide, Australia.|South Australian Health and Medical Research Institute, Adelaide, Australia.
Elina
E
Hyppönen
D002112:Calcifediol; D002853:Chromatography, Liquid / Q000379:methods* / Q000592:standards; D015331:Cohort Studies; D005387:Finland; D006801:Humans; D016014:Linear Models; D008403:Mass Screening / Q000379:methods / Q000592:standards; D011863:Radioimmunoassay / Q000379:methods* / Q000592:standards; D015203:Reproducibility of Results; D053719:Tandem Mass Spectrometry / Q000379:methods* / Q000592:standards; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
D014807:Vitamin D; C104450:25-hydroxyvitamin D; D002112:Calcifediol
25(OH)D; assay; limits of agreement; population study; reliability; replication; vitamin D