The relationship between EPO and FGF23 metabolism. (A) Schematic overview of the EPO-FGF23 signaling pathway in the erythroid lineage in bone marrow. Phase 1 shows FGF23 production, the secretory process, and FGF receptor binding; phase 2 summarizes the effects of a decrease in the i:cFGF23 ratio. (B) Correlation between C-terminal FGF23 and EPO. Individual patient data are represented as disease and transfusion requirement. Correlation between total FGF23 and EPO in patients with various hemolytic anemias: r = +0.64; 95% CI, 0.09-0.89. The solid line represents the linear regression line; the dashed lines are the 95% CI bands. PKD, pyruvate kinase deficiency; SCD, sickle cell disease.