B-029 Analytical Performance Evaluation of the Double-Antibody Sandwich Mindray Total-Vitamin D Assay and Comparison Versus Liquid Chromatography Tandem Mass Spectrometry and Commercial Immunoassays

Abstract

Vitamin D plays an important role in maintaining calcium and phosphorus homeostasis. Vitamin D deficiency may lead to skeletal problems such as rickets, osteomalacia, progressive bone loss, and osteoporosis. As it has recently been implicated also in several non-skeletal diseases, requests for its measurement have increased exponentially. Assessment of vitamin D status by measurement of 25-hydroxyvitamin-D in most clinical laboratories is performed by immunoassays. In this study we provide analytical evaluation of the new sandwich chemiluminescent immunoassay from Mindray (Mindray total-Vitamin D-II) that is based on anti-metatype antibodies. Its clinical performance was compared with two commercial chemiluminescent immunoassays one competitive and one non-competitive and against a Vitamin D standardization Program Traceable liquid chromatography-tandem mass spectrometry (LC-MSMS) using clinical samples from Greek volunteer donors Mindray Vitamin D-II assay stability of calibration, precision, linearity, recovery, carry-over, limits of blank, detection and quantification were assessed by standard protocols. For the method comparison 163 (serum and K3-EDTA plasma) samples were obtained from healthy Greek donors. Correlation between methods was evaluated using Passing-Bablok and Bland-Altman analysis. Concordance correlation coefficient (CCC) was calculated in order to evaluate the agreement between methods Calibration proved to be stable for at lest 30 days, precision measured with kit controls as well as with in-lab prepared serum pools was excellent excellent showing CV’s at all levels <4.00%. The assay is linear at least up to 83 ng/mL. The limit of quantification was found to be 2.49 ng/mL and mean recovery was found to be 105.07% (95%CI 102.74-177.40). No carry-over was observed (Êrryover=0.03). Comparisons between serum and K3EDTA plasma exhibited excellent corelation K3EDTA=0.983*Serum+0.248 (r=0.990, p<0.0001) proving that both media can be used interchangeably with this assay (CCC=0.989). Comparison with the LC-MSMS showed excellent linear correlation Mindray=0.982*LC-MSMS-2.303 (r=0.986, p<0.0001) and only a small negative bias was observed (intercept=-2.303, 95%CI -2.908 to -1.785) that could be corrected with calibration as no proportional bias was detected. In our comparisons slope includes 1(0.982, 95%CI: 0.960-1.009). CCC was excellent (0.936) suggesting a good agreement between the two methods. Comparisons with the two commercial immunoassays showed also excellent correlations (r=0.966, p<0.0001 with the non-competitive immunoassay and r=0.968, p<0.0001 with the competitive immunoassay) The Mindray total-vitamin D-II assay demonstrated very good analytical performance correlated well with LC-MSMS and compared well with other immunoassays supporting its use in routine clinical practice