Office of Dietary Supplements, National Institutes of Health, Bethesda, MD, 20892, USA.
Vitamin D Standardization Program, LLC, Havre de Grace, MD, 21078, USA.
Anal Bioanal Chem. 2022 Nov;414(27):7793-7803. doi: 10.1007/s00216-022-04313-y. Epub 2022 Sep 16.
The majority of circulating 25-hydroxyvitamin D (25(OH)D) is protein bound and perhaps less available than the free fraction of 25(OH)D; therefore, researchers have proposed that the measurement of free 25(OH)D in human serum may be a better indicator of vitamin D health status than total 25(OH)D. The availability of a new enzyme-linked immunosorbent assay (ELISA) for the determination of free 25(OH)D provides a method for direct measurement of the low levels of non-protein bound 25(OH)D. As an initial step towards harmonization of measurements of free 25(OH)D, the ELISA was used to measure free 25(OH)D in three existing Standard Reference Materials (SRMs): SRM 972a Vitamin D Metabolites in Frozen Human Serum, SRM 2973 Vitamin D Metabolites in Frozen Human Serum (High Level), and SRM 1949 Frozen Prenatal Human Serum. Target values for free 25(OH)D in the nine SRM serum pools, obtained by combining the results from two laboratories, ranged from 3.76 ± 0.36 to 10.0 ± 0.58 pg/mL. Of particular significance is the assignment of free 25(OH)D target values to SRM 1949, which consists of four serum pools from non-pregnant female donors of reproductive age and pregnant women in each of the three trimesters and which also has values assigned for vitamin D binding protein, which increases during pregnancy. The availability of target values for free 25(OH)D in these SRMs will allow researchers to validate new analytical methods and to compare their results with other researchers as an initial step towards harmonization of measurements among different studies and laboratories.
循环中的大多数 25-羟维生素 D（25(OH)D）与蛋白质结合，可能不如游离 25(OH)D 部分可用；因此，研究人员提出，测量人血清中的游离 25(OH)D 可能比总 25(OH)D 更能反映维生素 D 的健康状况。一种新的酶联免疫吸附测定法（ELISA）可用于测定游离 25(OH)D，为直接测量非蛋白结合的低水平 25(OH)D 提供了一种方法。作为使游离 25(OH)D 测量标准化的初始步骤，该 ELISA 用于测量三个现有标准参考物质（SRM）中的游离 25(OH)D：冷冻人血清中的维生素 D 代谢物 SRM 972a、冷冻人血清中的维生素 D 代谢物 SRM 2973（高水平）和冷冻产前人血清 SRM 1949。通过合并两个实验室的结果，得到了 9 个 SRM 血清池中的游离 25(OH)D 目标值，范围为 3.76±0.36 至 10.0±0.58 pg/mL。特别重要的是，为 SRM 1949 分配了游离 25(OH)D 的目标值，该 SRM 由来自生育年龄的非妊娠女性供体和妊娠早期、中期和晚期的孕妇的四个血清池组成，并且还为维生素 D 结合蛋白赋值，后者在妊娠期间增加。这些 SRM 中游离 25(OH)D 的目标值的可用性将使研究人员能够验证新的分析方法，并将其结果与其他研究人员进行比较，作为在不同研究和实验室之间实现测量标准化的初始步骤。
