CHU Lille, UF 8832 Biochimie automatisée, Lille, France.
Centre de Biologie Pathologie, Laboratoire d'Hormonologie, Métabolisme-Nutrition, Oncologie, rue du Pr J. Leclercq, CHU Lille, F-59000 Lille, France.
Clin Chem Lab Med. 2020 Jan 28;58(2):222-231. doi: 10.1515/cclm-2019-0568.
Background Total blood calcium (TCa) is routinely used to diagnose and manage mineral and bone metabolism disorders. Numerous laboratories adjust TCa by albumin, though literature suggests there are some limits to this approach. Here we report a large retrospective study on agreement rate between ionized calcium (iCa) measurement and TCa or albumin-adjusted calcium measurements. Methods We retrospectively selected 5055 samples with simultaneous measurements of iCa, TCa, albumin and pH. We subgrouped our patients according to their estimated glomerular filtration rate (eGFR), albumin levels and pH. We analyzed each patient's calcium state with iCa as reference to determine agreement rate with TCa and albumin-adjusted calcium using Payne, Clase, Jain and Ridefelt formulas. Results The Payne formula performed poorly in patients with abnormal albumin, eGFR or pH levels. In patients with low albumin levels or blood pH disorders, Payne-adjusted calcium may overestimate the calcium state in up to 80% of cases. Similarly, TCa has better agreement with iCa in the case of hypoalbuminemia, but performed similarly to the Payne formula in patients with physiological albumin levels. The global agreement rate for Clase, Jain and Ridefelt formulas suggests significant improvement compared to Payne calcium adjustment but no significant improvement compared to TCa. Conclusions Total and albumin-adjusted calcium measurement leads to a misclassification of calcium status. Moreover, accurate calcium state determination depends on blood pH levels, whose measurement requires the same pre-analytical restrictions as iCa measurement. We propose that iCa should instead become the reference method to determine the real calcium state.
背景 总血钙（TCa）常用于诊断和管理矿物质和骨代谢紊乱。许多实验室通过白蛋白校正 TCa，但文献表明这种方法存在一些局限性。在此，我们报告了一项关于离子钙（iCa）测量与 TCa 或白蛋白校正钙测量之间一致性的大型回顾性研究。
方法 我们回顾性选择了 5055 例同时测量 iCa、TCa、白蛋白和 pH 的样本。根据估计肾小球滤过率（eGFR）、白蛋白水平和 pH 值对患者进行亚组分组。我们以 iCa 为参考，分析每个患者的钙状态，使用 Payne、Clase、Jain 和 Ridefelt 公式来确定与 TCa 和白蛋白校正钙的一致性。
结果 Payne 公式在白蛋白、eGFR 或 pH 值异常的患者中表现不佳。在白蛋白水平低或血液 pH 值异常的患者中，Payne 校正钙可能会高估钙状态，高达 80%的情况如此。同样，在低白蛋白血症的情况下，TCa 与 iCa 的一致性更好，但在生理白蛋白水平的患者中，其表现与 Payne 公式相似。Clase、Jain 和 Ridefelt 公式的总体一致性率表明与 Payne 钙校正相比有显著改善，但与 TCa 相比无显著改善。
结论 TCa 和白蛋白校正钙的测量会导致钙状态的错误分类。此外，准确的钙状态测定取决于血液 pH 值，其测定需要与 iCa 测量相同的预分析限制。我们建议 iCa 应成为确定真实钙状态的参考方法。
