The cross-harvest decrease in EPO concentrations and haemoglobin among those with IKI may reflect erythropoiesis limited by restricted EPO synthesis in kidney fibroblasts, as EPO increases in response to anaemia in individuals without CKD.37 Low ferritin levels (typically <30 μg/L) indicate iron deficiency, although concentrations increase with systemic inflammation. This evidence concerns the gene EPO and anemia (phenotype).