CPT code 85610: Prothrombin time, routine coagulation test2026 Medicare lab fee · Clinical Laboratory Fee Schedule
Measures how long citrated plasma takes to clot, commonly for warfarin monitoring and evaluation of bleeding or abnormal coagulation.
Medicare pays $4.29 for 85610 under the 2026 Clinical Laboratory Fee Schedule: one national amount, the same in every state and setting.
Medicare lab fee · CLFS 2026 Q4
National CLFS amount
$4.29
In effect since Jan 1, 2026. The same amount in every state, payment locality and setting.
- Geographic adjustment
- None
- Office vs facility
- Same
- Since 2020
- Unchanged
- QW · CLIA-waived test
- $4.29
Medicare pays the lesser of the lab’s charge and this amount. Patients usually owe no Part B deductible or coinsurance for covered clinical lab tests.
On this page 8 sections
What 85610 covers
The prothrombin time (PT) measures clot formation in a blood sample after reagents trigger the coagulation pathway. Laboratories generally test citrated plasma and report the PT in seconds; an international normalized ratio (INR) is commonly reported with it, particularly for monitoring warfarin therapy. Clinicians also order PT to assess unexplained bleeding or bruising, liver-related coagulation changes, and other suspected clotting abnormalities. Hospital and independent laboratories, as well as eligible office laboratories, perform the test.
Report 85610 for the routine PT test. CMS also lists a CLIA-waived version with modifier QW for eligible sites holding a CLIA certificate of waiver. Medicare pays the test through the CLFS, not the physician fee schedule. The 2026 national CLFS amount is $4.29; the same amount has applied each year from 2020 through 2026. The amount is the same across states and localities, with no office or facility payment difference.
This summary was written with AI assistance from CMS Clinical Laboratory Fee Schedule data. Amounts on this page come directly from CMS files.
How Medicare pays 85610
Clinical lab tests aren’t priced like physician services. They’re paid from their own fee schedule, with its own rules. See the whole lab fee schedule.
One national amount
CMS sets a single Clinical Laboratory Fee Schedule amount for 85610. There’s no geographic (GPCI) adjustment, so it pays the same in every state and payment locality.
No office or facility rate
Lab tests aren’t built from relative value units, so there’s no office and facility split: the place of service doesn’t change the CLFS amount.
Updated every quarter
CMS republishes the CLFS each quarter. New tests, often proprietary laboratory analyses (PLA codes), join during the year; existing amounts are updated each January.
Excluded from the physician fee schedule
The physician fee schedule lists 85610 with status X (excluded by statute), so the test itself is paid only from the CLFS.
CLIA-waived version (QW)
CMS also lists 85610 with modifier QW, the version labs holding a CLIA certificate of waiver bill. It pays $4.29.
85610 on the lab fee schedule since 2020
85610 · CLFS 2026 Q4 (current)
$4.29
Unchanged since Jan 1, 2020
27 quarterly CLFS releases on file, first CLFS 2020 Q1. A code missing from a quarter wasn’t on that release.
85610 compared with similar tests
- 85611PT substitutionPlasma fractions, each$3.94
- 85610 is the routine PT. Use 85611 for the specialized substitution test rather than a standard prothrombin time.
- 85730Partial thromboplastin timePTT, plasma or whole blood$6.01
- 85730 reports a partial thromboplastin time, not the prothrombin time measured by 85610. The two tests may be ordered together to assess different parts of coagulation.
- 85612Viper venom timeUndiluted assay$17.49
- 85612 is a venom-based coagulation test, not the routine PT reported with 85610.
- 85613Viper venom testDiluted clotting assay$9.58
- 85613 reports dilute Russell viper venom testing. It is distinct from the routine prothrombin time reported with 85610.
85610 billing questions
When should 85610 be reported instead of 85611?
Use 85610 for the routine prothrombin time. Code 85611 describes a specialized PT substitution test, rather than the standard clotting-time test.
Is the INR a separate test from the PT?
The INR is commonly calculated from the PT result, especially for warfarin monitoring. Reporting an INR with the PT does not by itself make it a separate laboratory test.
When is modifier QW appropriate?
Use QW for the CLIA-waived version when the testing site holds a CLIA certificate of waiver and performs the waived test.
How does Medicare pay 85610?
Medicare pays it under the CLFS at one national amount, without locality or office-versus-facility variation. The test is excluded from the physician fee schedule.
How is 85610 different from a PTT?
85610 measures prothrombin time and is commonly used for warfarin monitoring. Code 85730 reports a partial thromboplastin time, a different coagulation test.
Where this amount comes from
FeeBase reads lab amounts directly from the CMS Clinical Laboratory Fee Schedule file for the quarter: one row per code, with its payment indicator and national amount. Contractor-priced tests are labeled, never given a made-up amount. Amounts are Medicare payment limits, not a patient’s bill or a commercial rate.
CMS CLFS 2026 Q4 · effective Oct 1, 2026 through the day before Jan 1, 2027
Show the CMS file line behind this amount
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