Which antipsychotic requires regular ANC monitoring and what is the typical threshold to start?

• A. Clozapine requires regular ANC monitoring; threshold is ANC ≥ 1,500 cells/µL to start.
• B. Olanzapine requires regular ANC monitoring; threshold is ANC ≥ 2,000 cells/µL.
• C. Haloperidol requires regular ANC monitoring; threshold is ANC ≥ 2,500 cells/µL.
• D. Risperidone requires regular ANC monitoring; threshold is ANC ≥ 1,000 cells/µL.

Answer: (A)

The main idea is that clozapine carries a unique risk of agranulocytosis, so it requires ongoing monitoring of the absolute neutrophil count. To begin clozapine safely, the ANC must be at least 1,500 cells per microliter. This threshold helps ensure the patient has a sufficient neutrophil reserve before starting a drug with a significant danger of severe neutropenia. Because of this risk, clinicians conduct regular ANC checks throughout treatment, typically with a baseline test, then weekly for the first several months, then less frequently as counts remain stable. Other antipsychotics do not require this routine ANC surveillance, which is why the specified threshold and monitoring are specific to clozapine.