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BETA v.3.0

2025 CPT code 80159

Clozapine therapeutic drug assay.

The code includes the measurement of norclozapine, a metabolite of clozapine. This assay is typically performed using methods such as liquid chromatography-tandem mass spectrometry (LC-MS/MS).

Modifiers may be applicable, such as 91 (repeat clinical diagnostic laboratory test) if the test is repeated on the same day, or 90 (reference outside laboratory) if sent to another lab for processing.

Medical necessity is established by the clinical need to monitor clozapine levels for therapeutic management or to evaluate potential toxicity. The documentation must support the reason for the assay being performed.

A laboratory professional performs the assay, analyzes the results, and reports the findings to the ordering physician.

In simple words: This test measures the amount of clozapine, an antipsychotic medication, in your blood to ensure the correct dosage and effectiveness.

This code represents a quantitative therapeutic drug assay for clozapine, including its metabolite norclozapine, used to monitor medication levels in serum, plasma, or whole blood.

Example 1: A patient with schizophrenia exhibiting worsening symptoms has their clozapine levels checked to assess medication adherence and adjust dosage if necessary., A patient starting clozapine therapy requires regular monitoring of drug levels to ensure therapeutic range and minimize adverse effects., A patient experiencing potential clozapine toxicity has their blood levels tested to guide treatment decisions.

The documentation should include the reason for testing, the date and time of sample collection, the type of specimen collected, and any relevant clinical information.

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