Vitamin K status and bone health: An analysis of methods for determination of undercarboxylated osteocalcin
Vitamin K status and bone health: An analysis of methods for determination of undercarboxylated osteocalcin
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DOI：
10.1210/jc.83.9.3258
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发表时间：
1998-09-01
影响因子：
5.8
通讯作者：
Rosen, H
中科院分区：
文献类型：
--
作者：
Gundberg, CM;Nieman, SD;Rosen, H
最近的研究表明，骨折风险与低羧基骨钙素增加有关。方法利用未完全羧化和完全羧化骨钙素与羟基磷灰石或硫酸钡结合的差异。我们评估了这些方法，发现结果随盐的量和制备而变化。此外，不能直接比较具有不同量的总骨钙素的患者样本。通过将数据表示为样品中总骨钙素的百分比，并使用来自多个结合曲线的多项式方程校正骨钙素的基础水平，来最大限度地减少羧化不足骨钙素测定中的误差。在没有这两种校正的情况下，观察到羧基化不足的骨钙素的估计误差为5-15%。当采用不同类型的测定（RIA、完整、N-末端）时，结果也会受到影响。在正常成人和儿童以及长期华法林治疗的患者中，未与羟基磷灰石结合的骨钙素百分比在用完整测定法测量时低于多克隆RIA。差异与N-末端骨钙素片段的量有关，其对羟基磷灰石的亲和力较低，并导致对未羧化骨钙素的可变高估。在一个针对未羧化骨钙素的试剂盒中，我们发现羧化和未羧化完整骨钙素之间有很好的区分。然而，该测定检测到大的骨钙素片段，并高估了它们的浓度高达350%。使用该试剂盒的患者与正常成人相比，未羧基化骨钙素的值没有差异，但当标准化为完整的骨钙素时，使用香豆素的患者未羧基化骨钙素的百分比高于对照组，正如预期。正常儿童中未羧基化骨钙素的试剂盒值高于同一受试者的完整值，因为试剂盒对儿童中升高的循环片段的反应性增加。因此，为了估计未羧基化骨钙素，必须小心标准化用于结合的羟基磷灰石或亚硫酸钡，以校正样品中骨钙素的基础水平，使用不检测小片段的免疫测定，并将结果表示为样品中总骨钙素的百分比。如果没有这些预防措施，低羧基骨钙素的评估是不可靠的。
Recent studies suggest that fracture risk is associated with increased undercarboxylated osteocalcin. Methods use differences in binding of undercarboxylated and fully carboxylated osteocalcin to hydroxyapatite or barium sulfate. We evaluated these methods and found that results varied with the amount and preparation of the salts. Furthermore, patient samples with differing amounts of total osteocalcin could not be directly compared. Errors in the determination of undercarboxylated osteocalcin were minimized by expressing data as the percent of the total osteocalcin in the sample, and correcting for the basal level of osteocalcin using a polynomial equation derived from multiple binding curves. Errors from 5-15% in estimation of undercarboxylated osteocalcin were observed without both of these corrections. When differing types of assays were employed (RIA, intact, N-terminal), results also were affected. In normal adults and children and in patients on long-term warfarin therapy, the percent osteocalcin not bound to hydroxyapatite was lower when measured with an intact assay than by a polyclonal RIA. Differences were related to the amount of N-terminal osteocalcin fragments, which had low affinity for hydroxyapatite and resulted in variable overestimation of undercarboxylated osteocalcin.In a kit specific for uncarboxylated osteocalcin, we found good discrimination between carboxylated and uncarboxylated intact osteocalcin. However, the assay detected large osteocalcin fragments and overestimated their concentration by up to 350%. Values for uncarboxylated osteocalcin were not different in patients on coumadin compared with normal adults with this kit, but when normalized to the total intact osteocalcin, percent uncarboxylated osteocalcin was greater in patients on coumadin than in controls, as would be expected. Kit values for uncarboxylated osteocalcin in normal children were higher than intact values in the same subject, because of the increased reactivity of the kit toward circulating fragments that were elevated in children.Thus, for estimation of undercarboxylated osteocalcin, care must be taken to standardize the hydroxyapatite or barium sulfite used for binding, to correct for the basal level of osteocalcin in the sample, to use immunoassays that do not detect small fragments, and to express the results as the percent of the total osteocalcin in the sample. Without these precautions, the assessment of undercarboxylated osteocalcin is not reliable.