Final answer:
The nurse should monitor for thromboembolus when clients are receiving hematopoietic agents.
Step-by-step explanation:
When monitoring clients receiving hematopoietic agents, the most important thing for the nurse to monitor for is thromboembolus. Thromboembolus refers to a blood clot that has formed within a blood vessel and can potentially cause a blockage in the vessel, leading to serious complications such as stroke, heart attack, or pulmonary embolism. These complications can be life-threatening, so it is crucial for the nurse to closely monitor for any signs or symptoms of a developing blood clot.