Test Overview

Test Methodology

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Test Usage

Therapeutic Drug Monitoring

Reference Range*

Clozapine: >350 ng/mL; Clozapine & Norclozapine: >450 ng/mL.

* Reference ranges may change over time. Please refer to the original patient report when evaluating results.

Test Details

Days Test Performed

Monday - Friday

Analytic Time

3 - 5 days

Soft Order Code


MiChart Code

Clozapine (Clozaril), Level

Test Updated

Update Type: Reference range changed

Updated Date: 06/03/2020



Clozapine, Plasma/Serum

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Laboratory Reference

Mayo CLZ (61657)

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Specimen Requirements

Offsite Collection Instructions

Collect specimen in a red top tube; do not use SST tube. Centrifuge, aliquot serum into a plastic container and refrigerate.

Rejection Criteria

SST tube not acceptable.


Yellow Top Tube
Red Top Tube

Normal Volume

1.0 mL serum

Minimum Volume

0.6 mL serum

Additional Information

Clozapine is an antipsychotic agent. Peak clozapine concentrations are reached in 1-6 hours following oral dosage. Elimination half-life is 4-16 hours once steady state levels have been reached. Norclozapine has minimal therapeutic activity. Test sent to Mayo Medical Laboratories; performed by Mayo New England.

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