EPO and chronic kidney disease: The etiology of anemia in CKD is multifactorial, including an inadequate production of erythropoietin (EPO), as well as iron deficiency (absolute or functional), inflammation, increased levels of uremic toxins (most of them derived from the gut microbiota), reduced red blood cell lifespan, or nutritional deficiencies (vitamin B12 and folic acid), among others [5].