CPT code 84439: Free T4, unbound thyroxine2026 Medicare lab fee · Clinical Laboratory Fee Schedule
Measures free thyroxine to assess thyroid function, investigate suspected thyroid disorders, or monitor response to thyroid treatment.
Medicare pays $9.02 for 84439 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
$9.02
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 84439 covers
The free thyroxine (free T4) assay measures the unbound portion of thyroxine circulating in blood. Physicians order it to evaluate suspected hypothyroidism or hyperthyroidism and to assess thyroid status during treatment. It is commonly interpreted with thyroid-stimulating hormone (TSH), because the results provide complementary information about thyroid function. Clinical laboratories perform the assay on a blood specimen.
Report 84439 for a free T4 assay performed; report separately performed TSH or other thyroid assays under their own codes. Medicare pays the test only through the Clinical Laboratory Fee Schedule (CLFS). The 2026 national CLFS amount is $9.02 and has remained unchanged since 2020. One amount applies in every state and locality, with no geographic adjustment or office-versus-facility 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 84439
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 84439. 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 84439 with status X (excluded by statute), so the test itself is paid only from the CLFS.
84439 on the lab fee schedule since 2020
84439 · CLFS 2026 Q4 (current)
$9.02
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.
84439 compared with similar tests
- 84436Total T4Total thyroxine$6.87
- Choose 84439 when the assay measures free T4; choose 84436 when it measures total T4.
- 84443TSH testThyroid-stimulating hormone$16.80
- Code 84443 reports a TSH assay, not a thyroxine assay. TSH and free T4 may be ordered together as separate tests.
- 84481Free T3Unbound T3 measurement$16.94
- Code 84481 measures free T3. Code 84439 measures free T4, a different thyroid hormone.
84439 billing questions
When should 84439 be used instead of 84436?
Use 84439 for a free T4 assay, which measures unbound thyroxine. Code 84436 represents a total thyroxine assay.
Is TSH included in 84439?
No. A separately performed TSH assay is reported with 84443; 84439 represents the free T4 assay.
Can 84439 be reported with a TSH test?
Yes, when both assays are performed and documented. They measure different aspects of thyroid function and are commonly ordered together.
What should the record support for 84439?
Documentation should identify the free T4 test performed and support the clinical reason for evaluating thyroid function, such as a suspected thyroid disorder or treatment monitoring.
How does Medicare pay for 84439?
Medicare pays 84439 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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