Harmonization of serum 25-hydroxycalciferol assay results from high-performance liquid chromatography, enzyme immunoassay, radioimmunoassay, and immunochemiluminescence systems: A multicenter study.
BACKGROUND
Remarkable disagreement among different systems of 25-hydroxy vitamin D 25(OH)D assay makes decision making for both clinical and community interventions very difficult. This study aimed to harmonize the results obtained from different 25(OH)D assay systems.


METHODS
A total of 275 serum samples were analyzed for 25(OH)D using DIAsource-enzyme immunoassay (EIA), DIAsource-radioimmunoassay (RIA), Roche-electrochemiluminescence (ECL), Diasorin-chemiluminescent immunoassay (CLIA), and high-performance liquid chromatography (HPLC), as the reference method. Serum intact parathyroid hormone (iPTH) was also measured in all samples. Between-system agreement and harmonization were evaluated using Bland-Altman analysis, receiver operating characteristic (ROC), and regression analysis.


RESULTS
Mean serum 25(OH)D concentrations and frequency distribution of vitamin D status showed a significant difference among the studied systems (P<.001 for both). Serum 25(OH)D assay results from all systems correlated with those from HPLC. As compared with HPLC, ECL showed a positive bias (+3.8 nmol/L), whereas CLIA had a negative bias (-11.9 nmol/L). Both EIA and RIA showed a more or less similar positive bias (8.0 and 8.1 nmol/L, respectively). Using serum iPTH-based 25(OH)D cutoff points, only ECL results became comparable to and without significant difference with HPLC. However, when system-specific cutoffs were defined based on HPLC results using regression equations, mean 25(OH)D and frequency distribution of vitamin D status were more harmonized compared with the other methods.


CONCLUSIONS
Our findings showed that with adjustment of circulating 25(OH)D based on HPLC, frequency distribution of vitamin D status, as judged by different methods, can be well harmonized with no statistically significant inter-system difference.
Laboratory of Nutrition Research, National Nutrition and Food Technology Research Institute and Faculty of Nutrition Sciences and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Bahareh
B
Nikooyeh
Health Reference Laboratories (HRL), Iran Ministry of Health, Tehran, Iran.
Siamak M
SM
Samiee
Health Reference Laboratories (HRL), Iran Ministry of Health, Tehran, Iran.
Marjan R
MR
Farzami
Department of Biostatistics, Faculty of Paramedicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Hamid
H
Alavimajd
Laboratory of Nutrition Research, National Nutrition and Food Technology Research Institute and Faculty of Nutrition Sciences and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Maliheh
M
Zahedirad
Laboratory of Nutrition Research, National Nutrition and Food Technology Research Institute and Faculty of Nutrition Sciences and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Ali
A
Kalayi
Laboratory of Nutrition Research, National Nutrition and Food Technology Research Institute and Faculty of Nutrition Sciences and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Nastaran
N
Shariatzadeh
Department of Biostatistics, Faculty of Paramedicine, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Nasrin
N
Boroumand
Health Reference Laboratories (HRL), Iran Ministry of Health, Tehran, Iran.
Elham
E
Golshekan
Health Reference Laboratories (HRL), Iran Ministry of Health, Tehran, Iran.
Yalda
Y
Gholamian
Laboratory of Nutrition Research, National Nutrition and Food Technology Research Institute and Faculty of Nutrition Sciences and Food Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
Tirang R
TR
Neyestani
D015652:25-Hydroxyvitamin D 2 / Q000097:blood*; D000328:Adult; D001774:Blood Chemical Analysis / Q000592:standards*; D002851:Chromatography, High Pressure Liquid / Q000592:standards*; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000592:standards*; D008163:Luminescent Measurements; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D015203:Reproducibility of Results; D055815:Young Adult
D015652:25-Hydroxyvitamin D 2
25-hydroxycalciferol; harmonization; high-performance liquid chromatography; immunoassay; vitamin D