Summary & Overview

CPT 85610: Prothrombin Time (PT) Test

CPT code 85610 denotes the prothrombin time (PT) laboratory assay, a widely used coagulation test that measures plasma clotting time and monitors anticoagulant therapy such as warfarin. Nationally, PT testing is a routine component of anticoagulation management, perioperative assessment, and workups for bleeding or clotting disorders, making it a high-volume laboratory service with implications for clinical quality and utilization oversight.

Key payers included in the discussion are Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare, and Medicare. Readers will find a concise explanation of the clinical purpose of CPT code 85610, typical sites of service, and the common contexts in which the test is ordered. The publication summarizes benchmark considerations, common billing practices, and policy-relevant issues affecting laboratory reimbursement and prior authorization trends at a national level.

This analysis provides clinicians, laboratory managers, and billing professionals with context on clinical utility, payer coverage patterns, and practical documentation points relevant to CPT code 85610. Data not available in the input will be identified where applicable.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicareCPT 85610prothrombin timelaboratorycoagulationanticoagulation monitoringPT testclinical diagnosticslaboratory billing

Billing Code Overview

CPT code 85610 describes a prothrombin time (PT) test, a laboratory assay that measures the time it takes plasma to clot after adding reagents such as calcium and tissue factor. The test is commonly used to assess the coagulation cascade and to monitor the effect of oral anticoagulant therapy (for example, warfarin/Coumadin) by detecting delays in clotting time.

Service Type: Laboratory diagnostic test — coagulation assay

Typical Site of Service: Clinical laboratory or hospital laboratory; specimen collection may occur in outpatient clinic, physician office, or inpatient setting

Data not available in the input.

Clinical & Coding Specifications

Clinical Context

A typical patient is an adult on chronic warfarin (Coumadin) therapy for atrial fibrillation presenting for routine anticoagulation monitoring. The patient arrives at an outpatient laboratory or hospital phlebotomy station where blood is drawn into citrate anticoagulated tubes. The specimen is processed to produce plasma, and reagents (calcium and tissue factor) are added to measure prothrombin time; results are reported as seconds and often converted to an International Normalized Ratio (INR) to assess anticoagulant effect. Results influence dosing adjustments by the ordering clinician and may prompt phone or portal communication, medication changes, or urgent evaluation if values are supratherapeutic or subtherapeutic. Typical sites of service include outpatient laboratory, physician office with phlebotomy, hospital inpatient laboratory, and emergency department laboratory. Typical clinical workflow: order placed by prescribing clinician; specimen collected by phlebotomist or nurse; testing performed in a clinical laboratory by medical technologists; result verified and routed to the ordering clinician; clinician documents interpretation and any medication changes in the medical record.

Coding Specifications

Modifier	Description	When to Use
`26`	Professional component	Use when billing only the professional component of laboratory interpretation when applicable (rare for automated PT but applicable if physician performs interpretation service separately).
`59`	Distinct procedural service	Use when PT is billed with another service on the same day that is separate and distinct.
`76`	Repeat procedure or service by same physician	Use when the PT test is repeated by the same provider within the same encounter due to an invalid specimen or technical issue.
`77`	Repeat procedure by another physician	Use when another qualified provider repeats the PT test.
`90`	Reference (outside) laboratory	Use when the specimen is sent to an outside or reference laboratory for the PT.
`91`	Repeat clinical diagnostic laboratory test	Use when a subsequent PT is performed on the same day to obtain a separate valid result.
`95`	Synchronous telemedicine service rendered via real-time interactive audio and video	Use when laboratory results are reviewed and discussed with the patient via telemedicine visit and payer allows modifier use.
`QW`	CLIA waived test	Use when PT is performed using a CLIA-waived point-of-care device (if the device/test is CLIA-waived).
`XU`	Unusual non-overlapping service	Use when billing PT in combination with other services where documentation supports that the PT was distinct and separate in an unusual way.
`XE`	Separate encounter	Use when PT is performed during a distinct encounter from other billed services.

Taxonomy Code	Specialty	Notes
`207Q00000X`	Hematology	Hematologists interpret coagulation testing and manage anticoagulation in complex patients.
`207L00000X`	Pathology	Clinical pathologists oversee laboratory methods, quality control, and result validation for coagulation testing.
`207R00000X`	Internal Medicine	Primary care and internists commonly order and act on PT/INR results for chronic anticoagulation management.
`207RH0000X`	Cardiology	Cardiologists manage anticoagulation for atrial fibrillation and mechanical valves and frequently order PT testing.
`217V00000X`	Clinical Laboratory Scientist	Laboratory professionals perform the assay and ensure analytic quality control.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`I48.91`	Unspecified atrial fibrillation	A common indication for warfarin therapy; PT/INR monitoring assesses anticoagulation efficacy.
`Z79.01`	Long term (current) use of anticoagulants	Describes patients on chronic oral anticoagulant therapy who require periodic PT/INR testing.
`D68.9`	Coagulation defect, unspecified	PT is used in the evaluation of suspected coagulation disorders.
`I82.401`	Acute embolism and thrombosis of unspecified deep veins of right lower extremity	Patients with venous thromboembolism are often anticoagulated and require PT monitoring.
`Z51.89`	Encounter for other specified aftercare	Follow-up care for anticoagulation management may include PT testing.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`36415`	Collection of venous blood by venipuncture	Performed immediately before `85610` to obtain the plasma specimen for PT testing.
`85613`	Prothrombin time; paradoxical — factor studies (if applicable)	Performed when additional coagulation factor analysis is needed beyond routine PT.
`85025`	Blood count; automated (CBC) with automated differential	Often ordered alongside PT to assess bleeding risk, hemoglobin, and platelets when evaluating anticoagulation status.
`99212`	Office or other outpatient visit, established patient (low complexity)	Clinician encounter code used when reviewing PT/INR results and adjusting anticoagulant dosing in the outpatient setting.
`96360`	Intravenous hydration, simple infusion (example supportive care)	Occasionally used in inpatient settings when coagulopathy requires supportive IV therapy; may occur in the clinical workflow following abnormal PT results.