Prior to initiating erythropoietin therapy in CKD patients, which laboratory parameter should be checked?

• A. Iron levels
• B. Vitamin B12
• C. Calcium
• D. Sodium

Answer: (B)

Before starting erythropoietin in CKD, the most important thing to confirm is that there is enough iron available for red blood cell production. EPO can stimulate the marrow to make more cells, but without iron the response is poor and iron deficiency can blunt or negate the treatment’s effectiveness. So checking iron status is essential.

The practical way to do this is to look at iron studies, especially ferritin and transferrin saturation (TSAT). Ferritin reflects stored iron, while TSAT reflects the iron currently available for erythropoiesis. In CKD, ferritin can be misleadingly elevated due to inflammation, so TSAT becomes particularly helpful to gauge true iron availability. If iron stores are low or TSAT is low, iron supplementation—often intravenous iron for those on dialysis—is typically needed to enable a good response to erythropoietin.

Vitamin B12 deficiency can cause anemia, but it is not the primary determinant of erythropoietin responsiveness in CKD. You’d consider B12 if there are signs suggesting a macrocytic pattern or neuropathy, not as the default prerequisite for starting EPO. Calcium and sodium aren’t directly involved in enabling or predicting the response to erythropoietin.