CPT 84166Laboratory

Protein e-phoresis/urine/csf

CPT code 84166 covers laboratory testing that separates and measures different proteins in urine or cerebrospinal fluid (the fluid around your brain and spine) using an electrical current technique called electrophoresis.

Showing rates for

National Average

Base Medicare rate

$17.14

This calculator gives a typical-case estimate using standard Medicare modifier rules. Actual payment depends on payer policies, documentation, code-specific CMS status indicators, and locality. Verify before billing.

RVU breakdown

Work RVU

0.37

PE RVU (NF)

0.15

MP RVU

0.01

Total RVU

0.53

Conversion factor: 32.3465 · Source: CMS MPFS RVU25A · Confidence: High

NCCI bundling edits

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Billing tips

Clearly document specimen type (urine vs. CSF) in the requisition and medical record, as payers may require this distinction for medical necessity review
Impact: Prevents denials for lack of specificity; CSF specimens typically have stronger medical necessity support for neurological conditions
Link to specific ICD-10 codes indicating abnormal protein findings, multiple myeloma, kidney disease, or MS to establish medical necessity per LCD requirements
Impact: Proper diagnosis linkage can prevent 15-30% of medical necessity denials, protecting the full $17.14 reimbursement
Do not bill 84166 on the same date as serum protein electrophoresis (84165) without clear documentation justifying both specimen types
Impact: Concurrent billing may trigger audits or denials; document separate clinical indications to support both tests
Verify frequency limitations in your MAC's LCD - many payers limit urine protein electrophoresis to specific intervals unless disease progression is documented
Impact: Frequency edits can deny claims; typical limit is once per 3-6 months for monitoring established diagnoses
For CSF protein electrophoresis, ensure documentation includes lumbar puncture or CSF collection procedure code (62270, 62328) to support specimen availability
Impact: Missing procedure documentation may trigger denials questioning specimen source validity
Use modifier 91 appropriately when repeat testing is medically necessary same day, and document the clinical reason in the medical record
Impact: Allows recovery of additional $17.14 for medically necessary repeat; without modifier, second test will be denied as duplicate

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Frequently asked questions

What is the Medicare reimbursement rate for CPT code 84166 in 2025?

The 2025 Medicare national average reimbursement rate for CPT 84166 is $17.14 for both facility and non-facility settings. This rate is calculated using a total RVU of 0.53 multiplied by the 2025 conversion factor of 32.3465. Actual payment may vary by geographic location based on locality adjustments.

What is the difference between CPT 84165 and 84166?

CPT 84165 is for serum protein electrophoresis (blood), while CPT 84166 is for protein electrophoresis of urine or cerebrospinal fluid. The specimen type determines which code to use. They can be billed together on the same date if both specimen types are medically necessary and properly documented with distinct clinical indications.

How often can CPT 84166 be billed for the same patient?

Frequency limitations vary by Medicare Administrative Contractor (MAC) Local Coverage Determination (LCD). Typical limits allow urine protein electrophoresis every 3-6 months for established diagnoses like multiple myeloma monitoring. More frequent testing requires documentation of disease progression, treatment changes, or new clinical findings. CSF testing frequency depends on specific neurological diagnosis protocols.

What diagnosis codes support medical necessity for CPT 84166?

Common supporting ICD-10 codes include C90.00 (multiple myeloma), C90.10 (plasma cell leukemia), R80.9 (proteinuria unspecified), N00-N07 series (glomerular diseases), G35 (multiple sclerosis), G37.9 (demyelinating disease), and R77.2 (abnormal protein findings). The diagnosis must clearly indicate why urine or CSF protein analysis is medically necessary.

Can CPT 84166 be billed with immunofixation on the same day?

Yes, CPT 84166 (protein electrophoresis) and CPT 86334 or 86335 (immunofixation) are commonly billed together as they are complementary tests. Protein electrophoresis identifies abnormal protein patterns, while immunofixation characterizes the specific type of abnormal immunoglobulin. Both are typically medically necessary when investigating monoclonal gammopathies.

What RVU values are assigned to CPT 84166 for 2025?

For 2025, CPT 84166 has a Work RVU of 0.37, Practice Expense RVU of 0.15 (both facility and non-facility), and Malpractice RVU of 0.01, totaling 0.53 RVUs. These values are from the CMS Medicare Physician Fee Schedule RVU25A released December 23, 2024.

Does CPT 84166 require a CLIA waiver to perform?

No, CPT 84166 cannot be performed under a CLIA waiver. Protein electrophoresis is classified as high-complexity testing under CLIA regulations and requires a CLIA certificate for high-complexity testing. The laboratory must have appropriate quality control, proficiency testing, and qualified personnel supervision as mandated for high-complexity procedures.