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Background: Resistance to erythropoiesis-stimulating agents (ESAs) has been observed in patients with chronic kidney disease (CKD) and it is associated with clinical outcomes. The presence of ESA resistance cannot always be explained by the known risk factors of the condition, suggesting that additional factors may be involved. We wanted to test the hypothesis that vitamin D insufficiency is associated with lower hemoglobin (Hb) and ESA resistance in patients on maintenance hemodialysis (HD). Methods: Data from patients receiving maintenance HD in a single dialysis center were extracted from the medical records in a retrospective chart review. Basic patient characteristics and laboratory data including Hb, serum albumin, intact parathyroid hormone and serum 25(OH)-cholecalciferol (25(OH)D₃) levels were collected. ESA dose and Kt/V were extracted from the dialysis charts. Correlation analysis and multivariate linear regression analysis were used to reveal potential independent associations between clinical and laboratory parameters and ESA resistance. Results: Data from 142 patients were analyzed. Serum 25(OH)D₃ concentration was significantly correlated with Hb (ρ = 0.186, p < 0.05) and also with ESA dose/Hb index (ρ = 0.230, p < 0.01). In multivariable regression analyses, serum 25(OH)D₃ concentration remained significantly associated with both Hb and ESA dose/Hb index after controlling for potentially important confounders. Conclusion: Serum 25(OH)D₃ concentration is independently associated with erythropoietin responsiveness in CKD patients on maintenance HD. If this association will be confirmed, treatment trials looking at the effect of vitamin D supplementation on anemia treatment in CKD patients may be warranted.

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Increased bone fragility in dialysis patients is associated with vitamin D deficiency and relative hypoparathyroidism in addition to reduced BMD at the radius. Further studies are needed to determine whether patients with vitamin D deficiency benefit from vitamin D supplementation to reduce fracture risk.

Low PTH levels are not associated with low BMD in patients with end-stage kidney disease. Furthermore, bone metabolism seems to be independent of iPTH in patients with relative hypoparathyroidism likely reflecting skeletal resistance to PTH.