Summary & Overview
CPT 86359: T‑Cell Total Count, Laboratory Test
CPT code 86359 represents a lab assay that measures the total number of T cells in a patient specimen, most commonly blood. This test informs evaluation of immune‑suppressed patients and aids differentiation between malignant and nonmalignant hematologic or bone marrow disorders. The code is nationally relevant because T‑cell enumeration supports diagnosis, staging, and monitoring across oncology, immunology, and infectious disease care pathways.
Key payers addressed in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise clinical context for the assay, expected sites of service, and what typical coverage considerations look like across major commercial plans and Medicare. The publication summarizes common billing modifiers and service line implications, plus where clinical documentation and test indication influence coverage decisions.
This overview helps clinicians, laboratory administrators, and coding staff understand the clinical role of CPT code 86359, common operational settings for testing, and the payer landscape to consult when preparing claims. Data not available in the input is noted where applicable.
Billing Code Overview
CPT code 86359 describes a laboratory test performed by a lab analyst to measure the total number of T cells in a patient specimen, typically a blood sample. The test is used when a clinician needs to evaluate immune function — for example, when there are signs of an immune‑weakening disease — or to help differentiate cancerous from noncancerous hematologic or bone marrow conditions.
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Service type: Laboratory diagnostic test measuring T‑cell total count
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Typical site of service: Hospital laboratory, independent clinical laboratory, or outpatient laboratory where blood specimens are collected and analyzed
Clinical & Coding Specifications
Clinical Context
A 52-year-old patient with a history of unexplained recurrent infections and recent weight loss presents to the hematology clinic. The ordering provider suspects an underlying immunodeficiency or hematologic malignancy and requests a T‑cell total count to quantify circulating T lymphocytes. A phlebotomy appointment is scheduled at an outpatient laboratory; a trained phlebotomist collects a peripheral blood specimen into appropriate anticoagulant tubes. The specimen is sent to the clinical immunology laboratory where a technologist performs flow cytometry or another validated assay to enumerate total T cells (CD3+). Results are reviewed by a laboratory director or pathologist and reported to the ordering provider; abnormal results prompt additional testing (for example, CD4/CD8 subset analysis, immunoglobulin levels, bone marrow biopsy) and clinical correlation with the patient’s symptoms and imaging studies.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when only the professional interpretation or report is billed separately from the technical component of the laboratory test |
TC | Technical component | Use when billing only the laboratory’s technical component (equipment, reagents, personnel) of the test |
59 | Distinct procedural service | Use when the T‑cell count is a separate service from other procedures on the same day and not typically reported together |
90 | Reference (outside) laboratory | Use when the specimen is sent to an outside reference laboratory and the ordering lab bills for the test performed elsewhere |
91 | Repeat clinical diagnostic lab test | Use when reporting an immediate repeat test on the same day for reliability or acute clinical change |
52 | Reduced services | Use when the test was partially performed or abbreviated and not performed to full protocol |
53 | Discontinued procedure | Use when specimen collection or testing was started but discontinued for valid clinical reasons |
76 | Repeat procedure by same physician (Note: not in provided list) | Data not available in the input. |
90 | Duplicate entry avoided | Data not available in the input. |
QK | Qualified nonphysician practitioner with direct supervision (when applicable) | Use when a qualified nonphysician practitioner performs aspects of specimen collection under required supervision |
| Taxonomy Code | Specialty | Notes |
|---|---|---|
| Data not available in the input. | Hematology | Hematologists commonly order and interpret T‑cell counts for suspected blood cancers and marrow disorders |
| Data not available in the input. | Allergy and Immunology | Allergy/immunology specialists evaluate immune deficiency and monitor T‑cell counts for immunologic disorders |
| Data not available in the input. | Clinical Pathology / Laboratory Medicine | Pathologists and clinical laboratory directors oversee performance and reporting of immunophenotyping tests |
| Data not available in the input. | Infectious Disease | Infectious disease physicians may order T‑cell enumeration when evaluating opportunistic infections and immune status |
Related Diagnoses
| ICD-10 Code | Description | Clinical Relevance |
|---|---|---|
D84.9 | Immunodeficiency, unspecified | T‑cell counts are ordered to evaluate suspected primary or secondary immunodeficiency |
D70.9 | Neutropenia, unspecified | Concurrent immune cell counts help assess broader hematologic dysfunction when infections occur |
C91.0 | Acute lymphoblastic leukemia | T‑cell enumeration and immunophenotyping assist in characterizing lymphoid malignancies |
C91.5 | Mature T‑cell leukemia/lymphoma | Directly relevant when diagnosing or monitoring T‑cell lineage hematologic cancers |
B20 | Human immunodeficiency virus [HIV] disease | T‑cell counts, particularly CD4, are essential for staging and guiding management in HIV infection |
Related CPT Codes
| CPT Code | Description | Relationship to This Procedure |
|---|---|---|
86359 | Immunoassay for T‑cell enumeration (total T cells) | Primary test to measure circulating T lymphocyte count via immunologic assay or flow cytometry |
86361 | Immunoassay for T‑cell subset, e.g., CD4 or CD8 | Performed after or alongside total T‑cell count to define subsets when indicated |
85241 | Flow cytometry, immunophenotyping (peripheral blood), basic panel | Often used as the technical method to enumerate and phenotype T cells alongside total count |
36415 | Collection of venous blood by venipuncture | Specimen collection code commonly billed or documented in the clinical workflow prior to performing the T‑cell test |
85025 | Complete blood count (CBC) with automated differential | Frequently ordered concurrently to provide additional hematologic context for abnormal T‑cell counts |