CPT code 80186: Phenytoin level, unbound concentration2026 Medicare lab fee · Clinical Laboratory Fee Schedule
Measures unbound phenytoin in a blood specimen, often to guide antiseizure dosing when protein binding may make the total level misleading.
Medicare pays $13.76 for 80186 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
$13.76
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
- CMS updates
- Quarterly
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 80186 covers
This assay measures the unbound, or free, phenytoin concentration in blood. Clinicians may order it to guide dosing when altered protein binding—such as with low albumin or impaired kidney function—can make total phenytoin less representative of the active drug concentration. Hospital and independent laboratories commonly perform and report the assay for patients receiving phenytoin therapy.
Report 80186 for the free phenytoin result; report 80185 separately when the total assay is also performed. Medicare pays this laboratory test through the CLFS at one national amount, with no locality or office-versus-facility adjustment. The 2026 national CLFS amount is $13.76, unchanged from 2020 through 2026. The test is paid only through the CLFS, not the physician fee schedule.
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 80186
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 80186. 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 80186 with status X (excluded by statute), so the test itself is paid only from the CLFS.
80186 on the lab fee schedule since 2020
80186 · CLFS 2026 Q4 (current)
$13.76
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.
80186 compared with similar tests
- 80185Phenytoin levelTotal drug concentration$13.25
- 80185 measures total phenytoin, including bound and unbound drug. Choose 80186 for the free concentration; both may be reported when both assays are performed.
- 80184Phenobarbital levelQuantitative drug assay$15.30
- 80184 measures phenobarbital, a different antiseizure medication, rather than phenytoin.
- 80175Lamotrigine levelQuantitative drug assay$13.25
- 80175 measures lamotrigine. Select the assay for the medication being monitored, rather than using it for phenytoin.
80186 billing questions
When should this code be used instead of 80185?
Use 80186 for the unbound phenytoin concentration and 80185 for the total concentration. A free level can help when altered protein binding makes the total level less representative of the active drug concentration.
Can free and total phenytoin be reported on the same date?
Yes, when both assays are ordered and performed. Report each assay under its own code.
What does 80186 measure?
It measures the unbound, or free, phenytoin concentration rather than the total concentration.
Does Medicare pay a different amount by location or setting?
No. The CLFS amount is national and applies across localities and office or facility settings.
Is physician interpretation paid under this code?
This code is paid through the CLFS. The test is excluded from the physician fee schedule.
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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