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Updated: Jun 5, 2025
A Semi-Automated and Reproducible Biological-Based Method to Quantify Calcium Deposition In Vitro
Published on: June 2, 2022
The different serum albumin assays influence calcium status in haemodialysis patients: a comparative study against
Osama Eisa1, Mohammed Dafaalla2, Mark Wright2
1Clinical Biochemistry Department, Leeds Teaching Hospitals NHS Trust, Leeds, UK.
Insights
Adjusted calcium measurements often miss hypocalcemia in hemodialysis patients. Measuring free calcium (fCa) is recommended for accurate assessment in stable hemodialysis patients, avoiding misclassification of calcium status.
Area of Science:
- Nephrology
- Clinical Chemistry
- Biochemistry
Background:
- Accurate calcium assessment is vital for managing hemodialysis (HD) patients.
- Discrepancies arise from various laboratory methods for albumin and calcium adjustment equations.
- Free calcium (fCa) serves as a gold standard for calcium status evaluation.
Purpose of the Study:
- To evaluate the impact of albumin assay methods (BCP vs. BCG) on calcium status determination.
- To compare the accuracy of adjusted calcium equations against free calcium (fCa) in stable HD patients.
Main Methods:
- Collected 103 paired serum and fCa samples from stable HD patients.
- Measured albumin using bromocresol purple (BCP) and bromocresol green (BCG) assays.
- Analyzed total calcium (T.Ca), phosphate, bicarbonate, and pH.
- Compared BCP- and BCG-based adjusted calcium equations against fCa using statistical methods.
Main Results:
- Unadjusted T.Ca showed 70% agreement with fCa, identifying 61% of hypocalcemic samples.
- Adjusted calcium equations (BCP/BCG-based) poorly predicted fCa, misclassifying over 50% of hypocalcemic samples.
- Both equations misclassified severe hypocalcemia as mild in 4.9% of patients.
Conclusions:
- Current practice using adjusted calcium may miss significant hypocalcemia in HD patients.
- The study recommends discontinuing calcium adjustment procedures for stable HD patients.
- Direct measurement of free calcium (fCa) is advised for accurate calcium status assessment.
Objectives:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
