What are the required blood work tests prior to starting Clozapine (clozapine) therapy?

From the Guidelines

Before starting clozapine, patients need comprehensive baseline blood work including a complete blood count (CBC) with differential to assess white blood cell (WBC) count and absolute neutrophil count (ANC), with a baseline WBC count of at least 3,500/mm3 1. The baseline blood work is crucial to assess the risk of agranulocytosis, a potentially fatal side effect of clozapine.

• The ANC must be assessed as part of the baseline CBC with differential.
• Additional baseline tests may include metabolic panel, liver function tests, lipid panel, hemoglobin A1c, and electrocardiogram to assess QTc interval, although these are not explicitly mentioned in the context of pre-clozapine workup in the provided evidence 1.
• The evidence emphasizes the importance of monitoring blood cell counts during clozapine treatment, with weekly blood cell counts obtained during the first 6 months of treatment, then every 2 weeks thereafter, including testing during the 4 weeks after the medication is stopped 1.
• It is also important to note that the use of concurrent medications that also have the potential to lower blood cell counts should be avoided 1.
• The patient's medical history, including any history of myeloproliferative disorder or a history of agranulocytosis or granulocytopenia on clozapine, should be carefully evaluated before starting therapy 1.

From the FDA Drug Label

Prior to initiating treatment with clozapine tablets, a baseline ANC must be obtained. The baseline ANC must be at least 1500/μL for the general population, and at least 1000/μL for patients with documented Benign Ethnic Neutropenia (BEN). The required blood work prior to starting clozapine includes a baseline Absolute Neutrophil Count (ANC) of at least 1500/μL for the general population and at least 1000/μL for patients with documented Benign Ethnic Neutropenia (BEN) 2.

From the Research

Clozapine Workup Blood Work Prior to Start

The blood work required prior to starting clozapine includes:

• Mandatory white blood cell monitoring, specifically absolute neutrophil count (ANC) monitoring, due to the risk of clozapine-associated agranulocytosis 3, 4, 5, 6
• Monitoring of ANC is crucial, especially during the first 18 weeks of treatment, as the risk of agranulocytosis is concentrated in this period 3
• The thresholds for discontinuing clozapine treatment are typically set at an ANC below 1.0 × 10^9/L 3
• The frequency of blood monitoring may vary, but it is generally recommended to monitor ANC weekly for the first 18 weeks, and then the frequency can be adjusted based on the patient's risk factors and medical history 3, 5

Key Blood Parameters to Monitor

• Absolute Neutrophil Count (ANC): This is the primary parameter to monitor, as agranulocytosis is a significant risk associated with clozapine treatment 3, 4, 5, 6
• White Blood Cell Count (WBC): This is also an important parameter to monitor, as it can indicate the overall health of the patient's immune system 3, 5

Special Considerations

• Benign ethnic neutropenia: This is a condition that can affect certain ethnic groups, particularly those of African descent, and may impact the interpretation of blood test results 4
• Genetic risk factors: Certain genetic variations may increase the risk of agranulocytosis, and genetic testing may be recommended for some patients 4, 6