Quantitative immunoassay for a non-antibody substance that has no analyte-specific CPT code, reported once per analyte measured.
- Medicare
- $0.00
- Work RVU
- 0
- Global, days
- Region
- General
Documentation requirements
What must appear in the operative or office note to support the claim.
Source · Editorial brief grounded in 3 cited references ↓
- Order identifying the exact analyte measured
- Clinical indication tied to the analyte
- Lab report with a quantitative result and immunoassay method
- Count of distinct analytes when billing more than one unit
- Note on why no specific CPT or PLA code applies
Applicable modifiers
Modifiers commonly billed with this code.
Source · AMA CPT modifier descriptors · CMS NCCI Policy Manual
What this code covers
Source · Editorial summary grounded in 3 cited references ↓
83520 is the general quantitative immunoassay code for analytes that are not antibodies and do not have their own CPT code. It is a fallback, and payers treat it that way. Expect more scrutiny than a named test gets.
In orthopedics it comes up with specialty biomarkers: certain synovial fluid or serum markers sent out during a painful arthroplasty workup, or bone metabolism markers ordered in a fragility fracture clinic. Before you code it, check whether the test now has a specific CPT code or a Proprietary Laboratory Analyses (U) code. Many branded tests do, and billing 83520 instead gets denied or downcoded.
Each distinct analyte is one unit. If the lab runs two different analytes this way, two units are fine with documentation of both. Repeat runs of the same analyte on the same day need modifier 91 and a clinical reason. Payment comes from the Clinical Laboratory Fee Schedule, and because the code is so open-ended, payers often ask for records before paying.
RVU & reimbursement
Component RVUs and Medicare national rate. Actual payment varies by GPCI locality.
Source · CMS Physician Fee Schedule, RVU26A · January 2026
| Work RVU | 0 |
| Practice expense RVU | 0 |
| Malpractice RVU | 0 |
| Total RVU | 0 |
| Medicare national rate | $0.00 |
| Global period | days |
Payment by site of service
Medicare pays different rates by setting. HOPD typically pays substantially more than ASC for the same procedure.
Source · CMS OPPS Addendum B·ASC HCPCS payment rates·2026
| Setting | Medicare rate (national) |
|---|---|
Office (PFS non-facility) Procedure performed in physician's office | $0.00 |
Common denial reasons
The recurring reasons claims for CPT 83520 get rejected.
Source · Editorial brief grounded in CMS NCCI edits, AAOS coding appeals, and cited references ↓
- Test has a specific CPT or PLA code
- Analyte considered investigational by the payer
- Units exceed the number of distinct analytes documented
- Diagnosis does not support the test
- Records request unanswered for an unlisted-style lab code
Frequently asked questions
Source · Generated from the editorial pipeline, verified against 3 cited references ↓
01Can I bill 83520 for a branded synovial fluid test?
02How many units of 83520 can I bill?
03Why do payers ask for records on 83520?
Sources & references
Editorial content was developed using the following public sources.
Mira Scribe
Mira Scribe captures the specific marker ordered and why, such as a suspected periprosthetic infection, giving the biller the detail a payer asks for on a records request.
See how Mira captures CPT 83520 documentation