Background Calcium can be measured as ionised (Ca-ionised) or albumin-adjusted total calcium (Ca-albumin). Current clinical guidelines predominantly utilise Ca-albumin, despite Ca-ionised being the gold standard. Discrepancies can occur between these measurement modalities and can lead to clinical dilemmas. It remains unclear how large these discrepancies are in older patients. This study investigated the discrepancies between Ca-ionised and Ca-albumin in geriatric patients. Methods This is an observational study of all geriatric patients (n = 876) in the Jeroen Bosch Hospital (January 2018 and January 2021) in whom both Ca-ionised and Ca-albumin were measured. Misclassification of calcaemic state (i.e. low, normal or high) was calculated (percentages), the measure of agreement was described using Cohen’s Kappa and for the continuous data Pearson’s correlation coefficient was used. Relevant categories of age and renal function were considered for effect modification effects and studied by interaction terms in a regression model. Results In one-third of the measurements, there was a misclassification. Ca-albumin measurements failed to identify 28% of hypocalcaemia. In 3.5%, hypercalcemia based on Ca-albumin was not confirmed by Ca-ionised. The correlation coefficient between Ca-ionised and Ca-albumin was 0.743 (P = 0.01) and measure of agreement by Kappa was 0.213 (P < 0.001). In the oldest old (≥ 85 years) and patients with eGFR <30 ml/min/1.73 m2 ,the agreement by Kappa was lower, with values of 0.192 and 0.104, respectively. Conclusion There is a discrepancy between Ca-albumin and Ca-ionised in one-third of the geriatric patients, leading to clinical dilemmas. In the oldest old and patients with renal dysfunction, this problem is most pronounced.

中文翻译：

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老年人群中校正钙与离子钙的差异：一项观察性研究

背景 钙可以以电离钙（Ca-ionized）或白蛋白调整总钙（Ca-白蛋白）的形式进行测量。尽管钙离子是金标准，但当前的临床指南主要使用钙白蛋白。这些测量方式之间可能会出现差异，并可能导致临床困境。目前尚不清楚老年患者的这些差异有多大。本研究调查了老年患者钙离子和钙白蛋白之间的差异。方法 这是一项针对 Jeroen Bosch 医院（2018 年 1 月和 2021 年 1 月）所有老年患者 (n = 876) 的观察性研究，其中测量了钙离子和钙白蛋白。计算了钙血症状态的错误分类（即低、正常或高）（百分比），使用Cohen's Kappa 描述一致性测量，并且对于连续数据使用Pearson 相关系数。年龄和肾功能的相关类别被考虑为效果修正效应，并通过回归模型中的交互项进行研究。结果 在三分之一的测量中，存在分类错误。钙白蛋白测量未能识别 28% 的低钙血症。 3.5% 的患者以钙白蛋白为基础的高钙血症未通过钙离子化得到证实。钙离子和钙白蛋白之间的相关系数为 0.743 (P = 0.01)，Kappa 一致性测量为 0.213 (P < 0.001)。在年龄最大的老年人（≥85岁）和eGFR<30ml/min/1.73m2的患者中，Kappa的一致性较低，分别为0.192和0.104。结论 三分之一的老年患者存在白蛋白钙和离子钙的差异，导致临床困境。在老年人和肾功能不全的患者中，这个问题最为明显。