CPT code 80185: Phenytoin level, total drug concentration2026 Medicare lab fee · Clinical Laboratory Fee Schedule
Measures total phenytoin concentration to monitor treatment, assess possible toxicity, or guide dose adjustment in patients receiving phenytoin.
Medicare pays $13.25 for 80185 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
$13.25
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 80185 covers
80185 measures total phenytoin concentration, including protein-bound and unbound drug. It is used to monitor phenytoin exposure in patients treated for seizure control, investigate possible toxicity, and inform dose adjustment. Neurologists, primary care clinicians, and other prescribers managing antiseizure treatment may order it; clinical laboratories perform and report the result. Because the total concentration includes bound and unbound drug, it differs from a free phenytoin assay, which measures the unbound portion.
Report 80185 for a total phenytoin assay; 80186 identifies a separately performed free-level assay. Medicare pays 80185 only through the CLFS, at one national amount across states and localities, with no office or facility payment difference. The 2026 national CLFS amount is $13.25, unchanged since 2020. The test is excluded from the physician fee schedule by statute.
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 80185
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 80185. 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 80185 with status X (excluded by statute), so the test itself is paid only from the CLFS.
80185 on the lab fee schedule since 2020
80185 · CLFS 2026 Q4 (current)
$13.25
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.
80185 compared with similar tests
- 80186Phenytoin levelUnbound concentration$13.76
- 80185 measures total phenytoin; 80186 measures only the unbound, free portion.
- 80184Phenobarbital levelQuantitative drug assay$15.30
- 80184 measures phenobarbital, a different antiseizure medication; it is not a phenytoin assay.
- 80175Lamotrigine levelQuantitative drug assay$13.25
- 80175 measures lamotrigine rather than phenytoin. Select the code for the drug actually assayed.
80185 billing questions
When should 80185 be used instead of 80186?
Use 80185 for the total phenytoin concentration. Use 80186 when the laboratory measures the free, unbound concentration.
Does the total phenytoin result include the free portion?
Yes. Total phenytoin includes both protein-bound and unbound drug; 80186 measures only the unbound portion.
Can total and free phenytoin assays both be reported?
The codes identify distinct measurements: total phenytoin and unbound phenytoin. Select the code or codes that match the assays performed.
How many units should be reported?
Report one unit for each total phenytoin assay performed. The code represents the total-level test, not a panel of drug assays.
How does Medicare pay for 80185?
Medicare pays 80185 through the CLFS at one national amount across localities, with no office or facility payment difference.
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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