Eisa Osama, Dafaalla Mohammed, Wright Mark, Faisal Muhammad, Stuart Kevin, Jassam Nuthar
Clinical Biochemistry Department, Leeds Teaching Hospitals NHS Trust, Leeds, UK.
Renal Department, Leeds Teaching Hospitals NHS Trust, Leeds, UK.
Clin Chem Lab Med. 2024 Dec 13;63(5):952-961. doi: 10.1515/cclm-2024-1030. Print 2025 Apr 28.
Accurate assessment of calcium levels is crucial for optimal management of regular Haemodialysis (HD) patients. Different calcium adjustment equations and albumin methods; including bromocresol purple (BCP) and bromocresol green (BCG) assays are employed by laboratories, which cause considerable discrepancies between reported results. The aim of this study is to assess the influence of albumin assays on calcium status in stable haemodialysis patients against free calcium (fCa) as a gold standard test.
A total of 103 paired serum and fCa samples were collected from a cohort of stable HD patients. Albumin levels were measured by either the BCP or BCG method, and samples were also analysed for the total calcium (T.Ca), phosphate, bicarbonate, and pH levels. The performance of BCG-based and BCP-based adjusted calcium equations was compared using Z-scores scatter plots, intraclass correlation coefficient and Cohen Kappa statistic, with fCa being the reference standard.
Unadjusted T.Ca achieved a 70 % overall classification agreement with fCa and identified 61 % of the "true" hypocalcaemic samples. Adjusted calcium concentrations, calculated by either BCP- or BCG-based equation, were poor predictors of fCa; with more than 50 % of the hypocalcaemic samples being misclassified as normocalcaemic. Notably, both equations misclassified the calcium status in 5 (4.9 %) patients with severe hypocalcaemia (i.e., potentially requiring calcium infusion) as mild hypocalcaemia.
Our study showed evidence of hidden hypocalcaemia being missed by the current practice of using adjusted calcium in HD patients. Therefore, we recommend abandoning the adjustment procedure in samples from stable HD patients in favour of fCa measurement.
准确评估钙水平对于规律血液透析（HD）患者的优化管理至关重要。不同的钙调整方程和白蛋白检测方法，包括溴甲酚紫（BCP）法和溴甲酚绿（BCG）法，被实验室采用，这导致报告结果之间存在相当大的差异。本研究的目的是以游离钙（fCa）作为金标准检测，评估白蛋白检测方法对稳定血液透析患者钙状态的影响。
从一组稳定的HD患者中总共收集了103对血清和fCa样本。采用BCP法或BCG法测量白蛋白水平，并且还对样本进行总钙（T.Ca）、磷酸盐、碳酸氢盐和pH水平的分析。以fCa作为参考标准，使用Z分数散点图、组内相关系数和科恩kappa统计量比较基于BCG和基于BCP的调整钙方程的性能。
未调整的T.Ca与fCa的总体分类一致性达到70%，并识别出61%的“真正”低钙血症样本。通过基于BCP或BCG的方程计算的调整钙浓度对fCa的预测效果较差；超过50%的低钙血症样本被误分类为正常钙血症。值得注意的是，两个方程都将5例（4.9%）严重低钙血症（即可能需要输注钙）患者的钙状态误分类为轻度低钙血症。
我们的研究表明，目前在HD患者中使用调整钙的做法存在遗漏隐匿性低钙血症的证据。因此，我们建议放弃对稳定HD患者样本的调整程序，而采用fCa测量。
