Ordering Recommendation

Optimize drug therapy and monitor patient adherence.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Timing of specimen collection: Predose(trough) draw - at steady -state concentration.


Plain red. Also acceptable: Lavender (K2 or K3EDTA) or pink (K2EDTA).

Specimen Preparation

Separate serum or plasma from cells within 2 hours of collection. Transfer 1 mL serum or plasma to an ARUP standard transport tube.(Min: 0.5 mL)

Storage/Transport Temperature


Unacceptable Conditions

Whole blood. Gel separator tubes, light blue (citrate), or yellow (SPS or ACD solution).


After separation from cells: Ambient: 24 hours; Refrigerated: 1 week; Frozen: 3 months


Quantitative Liquid Chromatography-Tandem Mass Spectrometry




1-5 days

Reference Interval

Therapeutic Range Not well established
Toxic Level Total Clozapine and Metabolites: Greater than or equal to 1500 ng/mL

Interpretive Data

Therapeutic ranges are not well established. Clozapine is metabolized to norclozapine and clozapine-N-oxide. Clozapine concentrations between 100 and 700 ng/mL may correlate more with clinical response; however, nonresponsiveness may also occur within this range. For refractory schizophrenia, clozapine concentrations greater than 350 ng/mL are suggested to achieve a therapeutic response.

Toxicity: Adverse effects to clozapine therapy may include tachycardia, drowsiness, hypotension, and seizures.

Therapeutic and toxic ranges are not well established in children.

Compliance Category

Laboratory Developed Test (LDT)


Hotline History


CPT Codes



Component Test Code* Component Chart Name LOINC
2013458 Clozapine, S/P, Quant 6896-5
2013459 Norclozapine, S/P, Quant 10992-6
2013460 Clozapine-N-Oxide, S/P, Quant 85497-6
2013461 Total Clozapine and Metabolites 12375-2
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


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Clozapine and Metabolites, Serum or Plasma, Quantitative