CPT code 83521: Free light chains, each light-chain type2026 Medicare lab fee · Clinical Laboratory Fee Schedule
Measures free kappa or lambda immunoglobulin light chains, commonly ordered to evaluate or monitor monoclonal plasma-cell disorders.
Medicare pays $17.27 for 83521 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
$17.27
In effect since Jan 1, 2026. The same amount in every state, payment locality and setting.
- Geographic adjustment
- None
- Office vs facility
- Same
- Since 2022
- 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 83521 covers
This assay measures free immunoglobulin kappa or lambda light chains, most commonly in a serum sample. Clinicians use the results when evaluating or monitoring monoclonal plasma-cell disorders, including multiple myeloma and monoclonal gammopathy. It is commonly ordered by hematologists and oncologists, and may be performed by a clinical laboratory serving an office or outpatient practice.
Report 83521 for each light-chain type measured; testing both kappa and lambda generally means two units. The code reports the assay measurement. Medicare pays it only through the CLFS, at one national amount regardless of locality or office versus facility setting. The 2026 national CLFS amount is $17.27, unchanged from 2022 through 2026.
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 83521
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 83521. 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 83521 with status X (excluded by statute), so the test itself is paid only from the CLFS.
83521 on the lab fee schedule since 2022
83521 · CLFS 2026 Q4 (current)
$17.27
Unchanged since Jan 1, 2022
20 quarterly CLFS releases on file, first CLFS 2022 Q1. A code missing from a quarter wasn’t on that release.
83521 compared with similar tests
- 83520Quantitative immunoassayNot otherwise specified$17.27
- 83521 is specific to free immunoglobulin light chains, each type. Use 83520 for a quantitative immunoassay when no more specific code describes the analyte.
- 84165Protein electrophoresisSerum fractionation and quantitation$10.74
- 84165 evaluates serum protein fractions by electrophoresis; 83521 measures free kappa or lambda light chains.
- 86334ImmunofixationSerum specimen$22.34
- 86334 is serum immunofixation, which identifies and characterizes immunoglobulin components. 83521 quantifies free light-chain types.
83521 billing questions
How many units are reported when both kappa and lambda are measured?
The code is for each free light-chain type measured. When both kappa and lambda are tested, report two units.
Is 83521 the same as serum protein electrophoresis?
No. 83521 measures free kappa or lambda light chains; serum protein electrophoresis separates and evaluates protein fractions under 84165.
Can immunofixation be reported with 83521?
Yes, when separately ordered and performed as part of the clinical evaluation. Immunofixation is a distinct test reported with 86334.
Does Medicare pay a separate interpretation for 83521?
Medicare pays 83521 through the CLFS; the code reports the assay measurement.
Does the CLFS amount vary by locality or setting?
No. Medicare uses one national amount for 83521 across localities, with no office-versus-facility 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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