Supplementary Material for: Relationship between Anemia and Serum Concentrations of Calcium and Phosphorus in Advanced Non-Dialysis-Dependent Chronic Kidney Disease

Background/Aims: Different biochemical abnormalities of metabolic bone disease have been associated with anemia of chronic kidney disease (CKD), mainly in hemodialysis patients. However, all of these abnormalities are closely inter-related and their individual effect on the development of anemia is uncertain. This study was aimed to assess the relationship between anemia and a set of metabolic bone disease biomarkers in a cohort of adult patients with advanced non-dialysis-dependent CKD. Methods: The sample consisted of 382 patients submitted to a Nephrology Unit for evaluation of advanced CKD in a tertiary hospital from Gran Canaria during 3 years. Associations between anemia and serum levels of calcium (albumin-corrected), phosphorus, PTH, 25-hydroxivitamin D (25(OH)D3) and alkaline phosphatase were analyzed by using logistic regression models with adjustment for other demographic, clinical and biochemical covariates potentially related to anemia and to bone mineral metabolism. Results: Serum levels of calcium and 25(OH)D3 (negatively) and phosphorus (positively) were significantly associated with anemia in an unadjusted logistic regression model. In a fully adjusted multivariable model, the OR for anemia was 0.29 (95% CI 0.16-0.49; p < 0.0001) for every 1 mg/dl increase in serum calcium and 2.19 (95% CI 1.55-3.15; p < 0.001) for every 1 mg/dl increase in serum phosphorus. Female sex and lower serum albumin levels were also independently associated with anemia. The inclusion of albumin in the adjusted model displaced the significance of 25(OH)D3. Conclusions: Circulating levels of calcium and phosphorus are strongly linked to anemia in patients with advanced non-dialysis CKD.