Cross-reactivity of 25-hydroxy vitamin D2 from different commercial immunoassays for 25-hydroxy vitamin D: an evaluation without spiked samples.

摘要

Although there is still no consensus on 25-hydroxy vitamin D [25(OH)D] serum concentration below which vitamin D insufficiency is define.d, there is agreement that it should be somewhere between 20 and 40 ng/mL, with a clear preference for a value around 30-32 ng/mL (1-3). Many physicians evaluate serum 25(OH)D concentrations in vitamin D-treated patients to adjust the vitamin D dosage. While vitamin D synthesized in the skin during UVB exposure is vitamin D3, and the (rare) dietary sources of vitamin D are primarily vitamin D3, vitamin D2 is often provided as a vitamin D supplement in many countries. In these countries, measuring 25(OH)D in patients treated with vitamin D2 using a 25(OH)D assay that measures 25(OH)D2 poorly may lead to an incorrect diagnosis of vitamin D insufficiency, with potential harm (4). However, evaluating the cross-reactivity for 25(OH)D2 of a 25(OH)D assay is not easy. Due to the hydrophobic nature of 25(OH)D and the presence of large concentrations of vitamin D binding protein, matrix effects may be a problem when evaluating the recovery of a known amount of 25(OH)D2. For example, the percent recovery using the 25-hydroxy vitamin D2 was much better according to the manufacturer (75%) compared to that found by the DEQAS in 2005 (29%) (5) or by Hollis (21%-29%) (6). However, samples spiked with 25(OH)D2 are not suitable for evaluating the cross-reactivity of most immunoas-says for this compound (5), and serum from patients taking vitamin D2 supplements are necessary for this purpose. Thus, we propose a simple method to evaluate the ability of several commercial 25(OH)D assays to measure both 25(OH)D2 and 25(OH)D3 concentrations in serum from subjects treated with vitamin D2 in whom 25(OH)D2 and 25(OH)D3 were also measured separately using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method.