What labs should be obtained before starting clozapine (Clozaril)?

Required Laboratory Tests Before Starting Clozapine

Before initiating clozapine therapy, a comprehensive set of baseline laboratory tests must be obtained, including complete blood count with absolute neutrophil count (ANC), metabolic panel, and cardiovascular assessment. 1, 2

Mandatory Baseline Laboratory Tests

Hematological Monitoring

• Complete Blood Count (CBC) with differential 1, 2
  • Absolute Neutrophil Count (ANC) must be ≥1500/μL for general population
  • ANC must be ≥1000/μL for patients with documented Benign Ethnic Neutropenia (BEN)
  • This is critical due to the risk of severe neutropenia/agranulocytosis

Metabolic Parameters

• Fasting glucose or HbA1c 3
• Lipid panel (total cholesterol, LDL, HDL, triglycerides) 3
• Liver function tests (AST, ALT, bilirubin) 3, 1
• Renal function tests (BUN, creatinine) 3, 1
• Electrolytes 3

Cardiovascular Assessment

• Electrocardiogram (ECG) 3, 1
  • Essential to establish baseline QT interval
  • Helps identify pre-existing cardiac abnormalities
• Blood pressure measurement 3
  • Both standing and supine to assess for orthostatic changes

Anthropometric Measurements

• Body Mass Index (BMI) 3
• Waist circumference 3

Additional Considerations

Timing of Blood Draws

• Blood samples for CBC should ideally be drawn 12 hours after the last dose (trough level) 1
• Consider drawing blood after the patient has been awake for at least 2 hours, as early morning samples may show lower WBC/ANC values 4

Special Populations

• Women of childbearing age: Pregnancy test 3
• Patients with seizure history: Consider EEG baseline 2

Monitoring Schedule After Initiation

Once clozapine is initiated, regular monitoring is required:

• Weekly ANC monitoring for the first 6 months 1
• Biweekly monitoring for months 7-12 1
• Monthly monitoring after 12 months if ANC remains stable 1

Common Pitfalls to Avoid

1. Failing to establish proper baseline: Without baseline values, it's impossible to accurately assess changes that may occur during treatment

2. Overlooking cardiovascular assessment: Clozapine can cause myocarditis, cardiomyopathy, and orthostatic hypotension 2

3. Inadequate metabolic screening: Clozapine is associated with significant metabolic side effects including weight gain, hyperglycemia, and dyslipidemia 3

4. Morning blood draws: Early morning CBC samples may show artificially lower WBC/ANC values that could lead to unnecessary treatment interruption 4

By following these comprehensive baseline laboratory requirements, clinicians can minimize risks and establish appropriate monitoring parameters for safe clozapine therapy.