In preterm babies ESAs may help reduce the need for red blood cell transfusions.The 2020 Cochrane Anaesthesia Review Group review of Erythropoietin plus iron versus control treatment including placebo or iron for preoperative anaemic adults undergoing non‐cardiac surgery  demonstrated that patients were much less likely to require red cell transfusion and in those transfused, the volumes were unchanged (mean difference -0.09, 95% CI -0.23 to 0.05). Pre-op Hb concentration was increased in those receiving high dose EPO, but not low dose.There is no evidence that one agent is better than another in the setting of CKD. Failure
ESAs may fail to achieve an adequate therapeutic response when one or more of the following is present:
Occult blood loss and/or iron deficiency
Vitamin B12 or folate deficiency
Infection and inflammation
Inadequate dialysis
Hyperparathyroidism
Aluminum toxicity
Patient adherence
Hypothyroidism
Primary disease activity
Transplant rejection
Malignancy
Pure red cell aplasia

Types
The following types of ESAs are available:
Erythropoietin (Epo)
Epoetin alfa (Procrit, Epogen)
Epoetin beta (NeoRecormon)
Epoetin zeta (Silapo, Retacrit)
Darbepoetin alfa (Aranesp)
Methoxy polyethylene glycol-epoetin beta (Mircera)

Available forms
Recombinant erythropoietin has a variety of glycosylation patterns giving rise to alpha, beta, delta, and omega forms:

Darbepoetin alfa, which early literature during its development often termed as novel erythropoiesis-stimulating protein (NESP), is a form created by five substitutions (Asn-30, Thr-32, Val-87, Asn-88 and Thr-90) that create two new N-glycosylation sites. This glycoprotein has a longer terminal half-life, meaning it is possible to administer it less frequently. Misuse
Erythropoiesis-stimulating agents have a history of use as blood doping agents in endurance sports, such as horseracing, boxing, cycling, rowing, distance running, race walking, snowshoeing, cross country skiing, biathlon, mixed martial arts, and triathlon.
Drug Information Portal. U.S. National Library of Medicine.