Abstract

Background: Albumin-corrected calcium (cCa) is recommended over ionized calcium (iCa) in hemodialysis (HD) patients per the Kidney Disease: Improving Global Outcomes position statements due to cost and feasibility. Two common albumin assays, bromocresol green (BCG) and bromocresol purple (BCP), produce differing results in uremic patients. All previous studies compared iCa to cCa from a BCG assay. This study, using the BCP assay, aimed to compare cCa and total calcium, respectively, to iCa. We also sought to assess phosphate binders and dialysis prescribing patterns following abnormal calcium measurements. Materials and methods: Retrospective review of 122 stable chronic HD patients with iCa, serum calcium, and albumin measured together throughout 6 blood work periods for a total of 338 sets of comparison values. Payne and Jain calcium correction equations were used. Prescription changes within 2 weeks of abnormal iCa values were recorded. Results: Mean iCa, cCa, and total calcium were 1.17 ± 0.08, 2.37 ± 0.16, and 2.28 ± 0.15 mmol/L, respectively. Total calcium and cCa compared to iCa had κ-coefficients of 0.19 and 0.08, respectively, for hypocalcemia, 0.19 and –0.02 for normocalcemia and 0.59 and 0.46 for hypercalcemia. 21 interventions were made in hypocalcemic patients using iCa as reference; however, if total or corrected calcium values were used, only 8 and 5 interventions, respectively, would result. Conclusion: When BCP assay is used, conventional correction equations should not be utilized in hemodialysis patients; uncorrected serum calcium has a better predictive value.


Author Details

Authors

• Wenxin Cindy Pan
• Wynnie Lau
• Andre Mattman
• Mercedeh Kiaii
• Beverly Jung

Departments

• St. Paul’s Hospital, Vancouver, BC, Canada

Address

Wynnie Lau, BSc (Pharm), ACPR, Pharm, D
St.
Paul’s Hospital
Vancouver, BC, Canada

Email: wlau@
providencehealth.bc.ca

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