Summary & Overview
CPT 85305: Total Protein S Level in Plasma
CPT code 85305 represents a laboratory diagnostic assay that quantifies total protein S levels in patient plasma. Protein S testing is clinically important for evaluating inherited or acquired thrombophilia and for guiding anticoagulation-related clinical decisions. Nationally, accurate coding and coverage determinations for protein S testing affect laboratory reimbursement, utilization monitoring, and access to targeted coagulation diagnostics.
Key payers in this analysis include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise clinical context for the assay, standard sites of service, and an overview of typical billing considerations. The publication also summarizes benchmarking approaches and payer coverage patterns where available, highlights relevant coding relationships, and outlines common modifiers and service-line implications for laboratories and hospital billing teams. Where payer-specific policy or reimbursement details are not provided in input data, the report indicates that such data are not available. The content is organized to help laboratory managers, billing professionals, and policy analysts understand how CPT code 85305 is used in clinical and administrative workflows and what documentation elements commonly accompany this diagnostic test.
Billing Code Overview
CPT code 85305 describes a laboratory assay in which the lab analyst measures the total protein S level in the patient’s plasma. This test evaluates the amount of protein S, a vitamin K–dependent plasma protein that plays a role in anticoagulation and thrombotic risk assessment.
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Service type: Laboratory diagnostic test (quantitative plasma protein assay)
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Typical site of service: Clinical laboratory or hospital laboratory setting
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Clinical & Coding Specifications
Clinical Context
A 42-year-old male with a history of unprovoked deep vein thrombosis (DVT) is referred to the outpatient hematology laboratory for thrombophilia evaluation. The ordering clinician requests a total protein S level to determine whether protein S deficiency may be contributing to the patient’s hypercoagulable state. The patient presents to a phlebotomy station at a hospital outpatient lab or independent clinical laboratory. A trained phlebotomist collects a citrated plasma sample, labels it with patient identifiers and collection time, and forwards the specimen to the laboratory. The laboratory analyst performs the 85305 assay to measure total protein S antigen concentration in plasma using an immunoassay or nephelometric method. Results are reviewed by the laboratory director and transmitted to the ordering hematologist. The typical site of service is an outpatient hospital laboratory, independent clinical laboratory, or hospital-based pathology lab. Turnaround time is usually 24–72 hours depending on batching and confirmatory testing.
Coding Specifications
| Modifier | Description | When to Use |
|---|---|---|
26 | Professional component | Use when billing only the professional interpretation or review portion if applicable for lab interpretation by a pathologist on separate claim. |