Efficacy of the Measurement of 25-Hydroxyvitamin D2 and D3 Levels by Using PerkinElmer Liquid Chromatography-Tandem Mass Spectrometry Vitamin D Kit Compared With DiaSorin Radioimmunoassay Kit and Elecsys Vitamin D Total Assay

Vitamin D2 (ergocalciferol) and D3 (cholecalciferol) can be procured from exogenous sources. These are then metabolized to 25-hydroxyvitamin D (25OHD2 and 25OHD3) in the liver. Measuring the levels of both 25OHD2 and 25OHD3 is imperative in assessing clinical nutritional status [1]. Vitamin D2 or D3 is provided as a vitamin D supplement in many countries. Serum 25OHD levels can be measured by competitive binding assay, RIA, automated immunoassay, HPLC, and by the recently developed liquid chromatography-tandem mass spectrometry (LC-MS/MS) technique. LC-MS/MS is considered as the “gold standard” for the detection and quantification of 25OHD2 and 25OHD3. The MS/MS Vitamin D kit from PerkinElmer (PerkinElmer, Waltham, MA, USA) is a commercial reagent kit, intended for the quantitative determination of 25OHD2 and 25OHD3. The MS/MS Vitamin D kit protocol was compared with the following assays: RIA from DiaSorin (DiaSorin, Stillwater, MN, USA) and automated electro-chemiluminescence immunoassay (ECLIA) from Roche (Roche Diagnostics GmbH, Mannheim, Germany). After receiving approval by the Ethics Review Board of the Cheil General Hospital and Women’s Healthcare Centre (Seoul, Korea), consecutive samples (n=50) sent for routine 25OHD analysis were used. The MS/MS Vitamin D kit was used along with the MS/MS Vitamin D Derivatization Box (PerkinElmer) on an LC-MS/MS system that included ACQUITY TQD tandem mass spectrometer (Waters, Milford, MA, USA). The MS/MS Vitamin D kit was compared with 25OHD 125I-based RIA kit and Elecsys Vitamin D Total assay. The MS/MS Vitamin D kit, RIA kit, and Elecsys Vitamin D Total assay were run according to the manufacturers’ specifications. All three assays were compared by linear regression and Bland-Altman plot. The correlation between the methods was compared by using Pearson’s correlation coefficient. Agreement in the assessment of the vitamin D status between methods was evaluated by using Cohen’s kappa [2]. Statistical analysis was performed by SPSS software (version 18.0.0, SPSS Inc. Chicago, IL, USA).