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Comparison of two methods for measurement of 25-hydroxyvitamin D

Background Measurement of circulating 25-hydroxyvitamin D (25(OH)D) in blood is the most reliable indicator of vitamin D status in organism. There are currently two main types of measurement used routinely for measuring the main circulating metabolites of vitamin D, 25(OH)D2 and 25(OH)D3. These are competitive immunoassay and methods based on chromatographic separation followed by non-immunological direct detection. With increasing clinical demand for 25(OH)D assays, fast automated platform with immunoassays are attractive. We evaluated an automated immunoassay for the quantitative determination of total serum 25(OH)D and compared it with a selective and sensitive HPLC method with UV detection. Methods 25(OH)D from human sera (routine serum samples, N=48) was measured using two methods: fully automated competitive electrochemiluminescence immunoassay (Roche Elecsys Vitamin D total assay) and Chromsystems HPLC method for 25(OH) D3/D2. The evaluation protocol for immunoassay consisted of within-run imprecision (10 sequential runs, two samples) and between-run imprecision (10 consecutive working days, 2 sequential runs) with commercial controls PreciControl Bone 1 and PreciControl Bone 2, inaccuracy (N=20), and method comparison. Methods were compared by Passing and Bablok regression and Bland-Altman analyses. Results Within-run imprecision for Roche Elecsys Vitamin D total assay was 2.56%, and between-run imprecision was 2.99% and 3.79%. Quality requirement for inaccuracy was fulfilled. The comparison with HPLC method demonstrated strong correlation (r =0.9581 ; y=0.918x-4.5082) and good agreement (bias = ±1.96 SD). Conclusion Roche Elecsys Vitamin D total assay showed good correlation and agreement with HPLC-UV method and represents an accurate and precise automated tool for serum total 25(OH)D determinations. Measurement of 25(OH)D by immunoassay is also the method of choice for reasons of convenience, speed, turnaround, and cost.

25-hydroxyvitamin D; methods comparison

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