CPT 80159: Clozapine Level Measurement

CPT code 80159 describes a laboratory test that measures the clozapine level in a patient’s specimen, a therapeutic drug monitoring service typically performed by a clinical laboratory using blood samples; service type: laboratory therapeutic drug monitoring; typical site of service: clinical laboratory or hospital laboratory performing blood-based testing.

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CPT 80159: Clozapine Level Measurement

Customize your policy alerts

Sign up for cpt 80159 policy alerts

Get alerted when payer policies referencing 80159 are released or updated.

Monitor payer policy activity

Receive email alerts as soon as relevant payer policies are published or updated.

Clinical & Coding Specifications

Clinical Context

A 38-year-old patient with treatment-resistant schizophrenia is receiving clozapine therapy under a monitored program. Periodic therapeutic drug monitoring is ordered to measure plasma clozapine concentration to assess adherence, efficacy, and risk of toxicity (including agranulocytosis and seizures). A clinician orders the clozapine level test when the patient reports increased sedation, confusion, or new seizures, after dose changes, or to confirm subtherapeutic levels when symptoms recur. A blood specimen is collected in an outpatient laboratory or hospital phlebotomy service, transported to the chemistry/toxicology laboratory, and analyzed using validated immunoassay or chromatography methods. Results are reported to the prescribing psychiatrist and documented in the medical record for dose adjustment and safety monitoring.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`80159`	Clozapine; quantitative	Primary test measuring plasma clozapine concentration for therapeutic monitoring.
`80480`	Clozapine metabolite testing; quantitative (example: norclozapine)	Often performed alongside clozapine testing to assess metabolism and adherence.
`36415`	Collection of venous blood by venipuncture	Specimen collection required prior to performing `80159`.
`80307`	Drug screen, qualitative; multiple drugs, any method	May be ordered with `80159` when evaluating adherence or concomitant substance use.
`99000`	Handling and/or conveyance of specimen to outside lab (historical/unlisted)	Administrative steps related to sending specimen to a reference laboratory (use depends on payer policy).

Related Modifiers

5 rows

Modifier	Description	When to Use
90	Modifier ‑90 (Reference/Outside Laboratory) indicates that a laboratory test was performed by an entity other than the treating or reporting provider. The American Medical Association defines…	- Use CPT modifier -90 when a laboratory test is performed by an outside/reference laboratory (an entity other than the treating or reporting physician or qualified professional) and the claim needs…
26	Modifier 26 (Professional Component) identifies and bills only the professional portion of a split service — the physician’s interpretation, report, and medical judgment — when the technical…	- Use CPT Modifier -26 when you are billing only the professional component (PC) of a split‑bill eligible service—i.e., you performed the physician interpretation, medical judgment and prepared a…
91	Modifier 91 — “Repeat Clinical Diagnostic Laboratory Test” — is appended when the exact same CPT laboratory test is performed more than once for the same patient on the same day because serial,…	- Use modifier 91 when the exact same CPT laboratory test is performed more than once on the same patient on the same date because serial or repeated testing is medically necessary to monitor…
74	Modifier ‑74 indicates an outpatient hospital or ASC procedure that was discontinued after anesthesia was administered and after the procedure had begun. Use this modifier when anesthesia (local,…	- Use modifier -74 when a procedure in an outpatient hospital or ASC setting is terminated after anesthesia has been administered and after the procedure has commenced (for example, after incision,…
52	Modifier ‑52 (Reduced Services) indicates that a service or procedure was partially reduced or omitted at the provider’s discretion, allowing reporting of the basic procedure number with a qualifier…	- Use modifier -52 when a physician or qualified health professional electively reduces or omits part of a procedure or service (for example, performing fewer required views or omitting a portion of…

Related Provider Taxonomies

8 rows

Taxonomy Code	Specialty	Notes
2084P0800X	Psychiatry Physician	A Psychiatrist specializes in the prevention, diagnosis, and treatment of mental disorders, emotional disorders, psychotic disorders, mood disorders, …
207L00000X	Anesthesiology Physician	An anesthesiologist is trained to provide pain relief and maintenance, or restoration, of a stable condition during and immediately following an opera…
207K00000X	Allergy & Immunology Physician	An allergist-immunologist is trained in evaluation, physical and laboratory diagnosis, and management of disorders involving the immune system. Select…
207LP4000X	Physician Nutrition Specialist (Anesthesiology)	A physician who specializes in the diagnosis and treatment of primary nutritional diseases (e.g., undernutrition, overnutrition, and genetic or acquir…
364SP0811X	Chronically Ill Psychiatric/Mental Health Clinical Nurse Specialist	Physician Assistants & Advanced Practice Nursing Providers · Clinical Nurse Specialist
311Z00000X	Custodial Care Facility	A facility providing care that serves to assist an individual in the activities of daily living, such as assistance in walking, getting in and out of …
225XF0002X	Feeding, Eating & Swallowing Occupational Therapist	Occupational therapists provide interventions to clients of all ages with feeding, eating and swallowing difficulties. Occupational therapists provid…
103TM1700X	Deactivated - Psychologist Men & Masculinity

Related ICD-10-CM Codes

27 rows

ICD-10-CM Code	Description
D68.9	Coagulation defect, unspecified
E03.9	Hypothyroidism, unspecified
E11.9	Type 2 diabetes mellitus without complications
F06.8	Other specified mental disorders due to known physiological condition
F20.0	Paranoid schizophrenia
F20.3	Undifferentiated schizophrenia
F20.9	Schizophrenia, unspecified
F25.0	Schizoaffective disorder, bipolar type
F25.1	Schizoaffective disorder, depressive type
F29	Unspecified psychosis not due to a substance or known physiological condition

Showing 1–10 of 27

CPT 80143: Acetaminophen Quantitative Assay

CPT-80145-ADALIMUMAB-LEVEL-ASSAY-THERAPEUTIC-DRUG-MONITORING

CPT 80145: Adalimumab Quantitative Drug Level Assay

CPT-80150-AMIKACIN-QUANTITATIVE-ASSAY-THERAPEUTIC-DRUG-MONITORING

CPT 80150: Amikacin Quantitative Serum Level

CPT-80151-AMIODARONE-QUANTITATIVE-SERUM-ASSAY

CPT 80151: Amiodarone Quantitative Drug Level Assay

CPT-80155-CAFFEINE-LEVEL-TESTING

CPT 80155: Caffeine Level Quantification

CPT-80156-CARBAMAZEPINE-TOTAL-LEVEL-LAB-ASSAY

CPT 80156: Carbamazepine Total Level (Serum)

CPT-80157-FREE-CARBAMAZEPINE-ASSAY

CPT 80157: Free Carbamazepine Quantitative Assay

CPT-80158-CYCLOSPORINE-QUANTITATIVE-ASSAY-LAB

CPT 80158: Cyclosporine Quantitation, Laboratory

CPT-80161-CARBAMAZEPINE-EPOXIDE-QUANTITATIVE-ASSAY

CPT 80161: Carbamazepine 10,11-Epoxide Level, Quantitative

CPT-80162-DIGOXIN-TOTAL-THERAPEUTIC-DRUG-MONITORING

CPT 80162: Total Digoxin Level in Serum

Showing 1–10 of 87

Frequently Asked Questions

References

1.CPT® Codes and Descriptions. AAPC. Retrieved Aug 11, 2026.Maintains the CPT code set's official descriptions and guidelines, licensed from the American Medical Association, used as the definitional source for CPT codes on this page.
2.HCPCS Quarterly Update. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's quarterly release of HCPCS Level II codes and short/long descriptors, the source for HCPCS code definitions and update history.
3.ICD-10-CM Full Code List. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's complete ICD-10-CM diagnosis code list, used to cross-reference diagnosis codes associated with this procedure or service.

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Trek Health ingests and normalizes Transparency in Coverage data and payer policy updates to give provider organizations a clear view of how commercial reimbursement behaves across markets, payers, and services. Our platform transforms raw payer disclosures into structured intelligence that supports contract evaluation, payer negotiations, and service line strategy. By combining market benchmarks with ongoing policy visibility, Trek helps teams identify variability, risk, and opportunity in commercial reimbursement. The result is faster insight, stronger negotiating positions, and more informed financial decisions.

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Clinical & Coding Specifications

Clinical Context

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`80159`	Clozapine; quantitative	Primary test measuring plasma clozapine concentration for therapeutic monitoring.
`80480`	Clozapine metabolite testing; quantitative (example: norclozapine)	Often performed alongside clozapine testing to assess metabolism and adherence.
`36415`	Collection of venous blood by venipuncture	Specimen collection required prior to performing `80159`.
`80307`	Drug screen, qualitative; multiple drugs, any method	May be ordered with `80159` when evaluating adherence or concomitant substance use.
`99000`	Handling and/or conveyance of specimen to outside lab (historical/unlisted)	Administrative steps related to sending specimen to a reference laboratory (use depends on payer policy).

Related Modifiers

5 rows

Modifier	Description	When to Use
90	Modifier ‑90 (Reference/Outside Laboratory) indicates that a laboratory test was performed by an entity other than the treating or reporting provider. The American Medical Association defines…	- Use CPT modifier -90 when a laboratory test is performed by an outside/reference laboratory (an entity other than the treating or reporting physician or qualified professional) and the claim needs…
26	Modifier 26 (Professional Component) identifies and bills only the professional portion of a split service — the physician’s interpretation, report, and medical judgment — when the technical…	- Use CPT Modifier -26 when you are billing only the professional component (PC) of a split‑bill eligible service—i.e., you performed the physician interpretation, medical judgment and prepared a…
91	Modifier 91 — “Repeat Clinical Diagnostic Laboratory Test” — is appended when the exact same CPT laboratory test is performed more than once for the same patient on the same day because serial,…	- Use modifier 91 when the exact same CPT laboratory test is performed more than once on the same patient on the same date because serial or repeated testing is medically necessary to monitor…
74	Modifier ‑74 indicates an outpatient hospital or ASC procedure that was discontinued after anesthesia was administered and after the procedure had begun. Use this modifier when anesthesia (local,…	- Use modifier -74 when a procedure in an outpatient hospital or ASC setting is terminated after anesthesia has been administered and after the procedure has commenced (for example, after incision,…
52	Modifier ‑52 (Reduced Services) indicates that a service or procedure was partially reduced or omitted at the provider’s discretion, allowing reporting of the basic procedure number with a qualifier…	- Use modifier -52 when a physician or qualified health professional electively reduces or omits part of a procedure or service (for example, performing fewer required views or omitting a portion of…

Related Provider Taxonomies

8 rows

Taxonomy Code	Specialty	Notes
2084P0800X	Psychiatry Physician	A Psychiatrist specializes in the prevention, diagnosis, and treatment of mental disorders, emotional disorders, psychotic disorders, mood disorders, …
207L00000X	Anesthesiology Physician	An anesthesiologist is trained to provide pain relief and maintenance, or restoration, of a stable condition during and immediately following an opera…
207K00000X	Allergy & Immunology Physician	An allergist-immunologist is trained in evaluation, physical and laboratory diagnosis, and management of disorders involving the immune system. Select…
207LP4000X	Physician Nutrition Specialist (Anesthesiology)	A physician who specializes in the diagnosis and treatment of primary nutritional diseases (e.g., undernutrition, overnutrition, and genetic or acquir…
364SP0811X	Chronically Ill Psychiatric/Mental Health Clinical Nurse Specialist	Physician Assistants & Advanced Practice Nursing Providers · Clinical Nurse Specialist
311Z00000X	Custodial Care Facility	A facility providing care that serves to assist an individual in the activities of daily living, such as assistance in walking, getting in and out of …
225XF0002X	Feeding, Eating & Swallowing Occupational Therapist	Occupational therapists provide interventions to clients of all ages with feeding, eating and swallowing difficulties. Occupational therapists provid…
103TM1700X	Deactivated - Psychologist Men & Masculinity

Related ICD-10-CM Codes

27 rows

ICD-10-CM Code	Description
D68.9	Coagulation defect, unspecified
E03.9	Hypothyroidism, unspecified
E11.9	Type 2 diabetes mellitus without complications
F06.8	Other specified mental disorders due to known physiological condition
F20.0	Paranoid schizophrenia
F20.3	Undifferentiated schizophrenia
F20.9	Schizophrenia, unspecified
F25.0	Schizoaffective disorder, bipolar type
F25.1	Schizoaffective disorder, depressive type
F29	Unspecified psychosis not due to a substance or known physiological condition

Showing 1–10 of 27

CPT 80143: Acetaminophen Quantitative Assay

CPT-80145-ADALIMUMAB-LEVEL-ASSAY-THERAPEUTIC-DRUG-MONITORING

CPT 80145: Adalimumab Quantitative Drug Level Assay

CPT-80150-AMIKACIN-QUANTITATIVE-ASSAY-THERAPEUTIC-DRUG-MONITORING

CPT 80150: Amikacin Quantitative Serum Level

CPT-80151-AMIODARONE-QUANTITATIVE-SERUM-ASSAY

CPT 80151: Amiodarone Quantitative Drug Level Assay

CPT-80155-CAFFEINE-LEVEL-TESTING

CPT 80155: Caffeine Level Quantification

CPT-80156-CARBAMAZEPINE-TOTAL-LEVEL-LAB-ASSAY

CPT 80156: Carbamazepine Total Level (Serum)

CPT-80157-FREE-CARBAMAZEPINE-ASSAY

CPT 80157: Free Carbamazepine Quantitative Assay

CPT-80158-CYCLOSPORINE-QUANTITATIVE-ASSAY-LAB

CPT 80158: Cyclosporine Quantitation, Laboratory

CPT-80161-CARBAMAZEPINE-EPOXIDE-QUANTITATIVE-ASSAY

CPT 80161: Carbamazepine 10,11-Epoxide Level, Quantitative

CPT-80162-DIGOXIN-TOTAL-THERAPEUTIC-DRUG-MONITORING

CPT 80162: Total Digoxin Level in Serum

Showing 1–10 of 87

Frequently Asked Questions

References

1.CPT® Codes and Descriptions. AAPC. Retrieved Aug 11, 2026.Maintains the CPT code set's official descriptions and guidelines, licensed from the American Medical Association, used as the definitional source for CPT codes on this page.
2.HCPCS Quarterly Update. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's quarterly release of HCPCS Level II codes and short/long descriptors, the source for HCPCS code definitions and update history.
3.ICD-10-CM Full Code List. Centers for Medicare & Medicaid Services (CMS). Retrieved Aug 11, 2026.CMS's complete ICD-10-CM diagnosis code list, used to cross-reference diagnosis codes associated with this procedure or service.

Published by

Trek Health powers OpenPayer with a leading commercial payer intelligence platform, seamlessly converting fragmented payer data into actionable insights for provider organizations.

OpenPayer

CPT 80159: Clozapine Level Measurement

Sign up for cpt 80159 policy alerts

OpenPayer

CPT 80159: Clozapine Level Measurement

Sign up for cpt 80159 policy alerts

Clinical & Coding Specifications

Clinical Context

Related CPT Codes

Related Modifiers

Related Provider Taxonomies

Related ICD-10-CM Codes

Related Codes

References

Clinical & Coding Specifications

Clinical Context

Related CPT Codes

Related Modifiers

Related Provider Taxonomies

Related ICD-10-CM Codes

Related Codes

References

CPT 80159: Clozapine Level Measurement

Sign up for cpt 80159 policy alerts

CPT 80159: Clozapine Level Measurement

Sign up for cpt 80159 policy alerts

Clinical & Coding Specifications

Clinical Context

Related CPT Codes

Related Modifiers

Related Provider Taxonomies

Related ICD-10-CM Codes

Related Codes

What does CPT code 80159 represent and when is it used?

How are specimen collection and testing components handled for clozapine level testing?

Which billing modifiers are relevant for 80159 and when should they be used?

Are there other CPT codes commonly billed with 80159?

Which specialties order or perform clozapine level testing and which payers are noted as covered?

References

Clinical & Coding Specifications

Clinical Context

Related CPT Codes

Related Modifiers

Related Provider Taxonomies

Related ICD-10-CM Codes

Related Codes

What does CPT code 80159 represent and when is it used?

How are specimen collection and testing components handled for clozapine level testing?

Which billing modifiers are relevant for 80159 and when should they be used?

Are there other CPT codes commonly billed with 80159?

Which specialties order or perform clozapine level testing and which payers are noted as covered?

References