Influence of the Assay for Measuring Serum Albumin on Corrected Total Calcium in Chronic Hemodialysis Patients

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The Japanese Society for Dialysis Therapy guideline for secondary hyperparathyroidism recommends the use of albumin-corrected serum Ca as a therapeutic target in chronic hemodialysis patients; however, the assay used for albumin measurement may affect the corrected Ca level. In this study, we examined the impact of the albumin assay on corrected Ca levels in hemodialysis patients. We measured serum albumin using bromocresol green (BCG) and modified bromocresol purple (BCP) assays, and corrected Ca for albumin using Payne's formula in 422 hemodialysis patients (age 66 ± 13 years; time on hemodialysis 116 ± 111 months). Serum albumin values were 3.7 ± 0.4 (1.4–4.6) g/dL by BCG and 3.3 ± 0.4 (1.0–4.3) g/dL by modified BCP, with the differences between the two assays ranging from 0.0 to 0.6 with a mean of 0.35 ± 0.09 g/dL. Serum C-reactive protein and globulin values were significantly higher in patients with differences in albumin greater than 0.5 g/dL (P < 0.01). Based on the BCG method, 71 patients (16.8%) were classified with hypocalcemia, 51 (12.1%) with hypercalcemia, and 300 (70.0%) as normocalcemic. In contrast, when using modified BCP, 33 patients (7.9%) were labeled as hypocalcemic, while 92 (21.8%) were hypercalcemic. Depending on the use of either BCG or modified BCP, a discrepancy of classification was observed in 79 patients (18.7%): 41 patients were re-classified from normocalcemic to hypercalcemic, and 38 patients were re-classified from hypocalcemic to normocalcemic by selecting the modified BCP assay. These findings suggest that the type of assay used for albumin measurement has an impact on albumin-corrected Ca levels.

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