A client on the inpatient psychiatric unit is taking the antipsychotic medication clozapine. Which assessment finding is most important for the nurse to report to the healthcare provider (HCP) immediately?

Clozapine is an atypical antipsychotic associated with a rare but life-threatening adverse effect: agranulocytosis, a severe reduction in white blood cells — specifically neutrophils — that dramatically impairs the body's ability to fight infection. Because of this risk, clients on clozapine require mandatory regular absolute neutrophil count (ANC) monitoring. Fatigue accompanied by fever is a classic early sign of agranulocytosis and potentially severe infection, and this combination must be reported to the healthcare provider immediately, as it may indicate that the client's white blood cell count has dropped to a dangerously low level. Delay in responding to these signs can be fatal. Recurrent insomnia is a common, non-urgent side effect of many psychiatric medications and does not require immediate reporting. Increased bruising may suggest thrombocytopenia rather than agranulocytosis and is worth monitoring but is less immediately life-threatening than signs of infection. Urinary frequency and urgency are associated with other adverse effects, such as urinary tract infections or diabetes, but are not among the most critical clozapine-specific concerns. The combination of fever and fatigue is the most alarming finding because it signals the possibility of agranulocytosis with active infection, requiring urgent laboratory evaluation and possible discontinuation of clozapine.