Which laboratory test must be monitored frequently in patients taking clozapine?

In patients taking clozapine, it is crucial to frequently monitor the white blood cell count (WBC) due to the risk of agranulocytosis, a potentially life-threatening reduction in the number of white blood cells. Clozapine is an atypical antipsychotic that has been associated with this serious adverse effect, which can increase the risk of infections.

To ensure patient safety, monitoring the WBC count allows healthcare providers to detect any decrease in white blood cells early on. This monitoring is mandated in clozapine treatment protocols, and the frequency of testing is often determined by the patient's current WBC count and absolute neutrophil count (ANC). If the WBC or ANC falls below specified thresholds, clozapine treatment may need to be adjusted or discontinued.

Other tests, such as liver function tests or thyroid function tests, may be relevant in the context of clozapine therapy, but they do not carry the same urgency and necessity for frequent monitoring as the WBC count, which directly relates to the risk of agranulocytosis associated with clozapine.