Final answer:
The nurse should monitor the client's hemoglobin level to determine the therapeutic effect of epoetin.
Step-by-step explanation:
The nurse should monitor the client's hemoglobin level to determine the therapeutic effect of epoetin. Epoetin is a medication that stimulates the production of red blood cells, which contain hemoglobin. An increased hemoglobin level indicates that the medication is working as intended by promoting the production of red blood cells and improving oxygen-carrying capacity in the body.