Summary & Overview

CPT 84166: Protein Fraction Electrophoresis, Nonserum Specimen

CPT code 84166 denotes electrophoretic analysis of protein fractions in specimens other than serum. This laboratory procedure separates and evaluates protein bands to help characterize abnormal protein distributions, monitor disease progression, or support diagnostic workflows in hematology, immunology and related specialties. Nationally, accurate coding for such laboratory tests matters for clinical communication, claims processing and payment consistency.

Key payers addressed include Aetna, Blue Cross Blue Shield, Cigna Health, UnitedHealthcare and Medicare. Readers will find a concise review of what the code represents, typical sites of service, common payer coverage considerations and benchmarking context where available. The publication summarizes clinical context for use of protein electrophoresis on nonserum specimens and highlights operational considerations relevant to laboratory and billing teams.

The report provides practical reference material: a clear code definition and clinical purpose, payer coverage scope, and items to check when submitting claims. Data not available in the input is noted where applicable. The content is organized to support billing staff, laboratory managers and policy analysts seeking a focused national overview of CPT code 84166.

AetnaBlue Cross Blue ShieldCigna HealthUnitedHealthcareMedicare84166CPTLaboratoryProtein ElectrophoresisClinical PathologyBilling and CodingLaboratory TestingNonserum Specimen

Billing Code Overview

CPT code 84166 describes an electrophoretic laboratory test in which the analyst separates and evaluates the levels of protein fractions in a specimen other than serum. This procedure involves laboratory processing and interpretation to identify and quantify distinct protein bands or fractions present in the submitted specimen.

Service type: Clinical laboratory electrophoresis of protein fractions
Typical site of service: Clinical laboratory or hospital laboratory setting

Clinical & Coding Specifications

Clinical Context

A 62-year-old patient with a history of chronic kidney disease and unexplained proteinuria is referred to the clinical laboratory for protein fractionation by electrophoresis on urine. The clinician orders 84166 to separate and quantify protein fractions in a non-serum specimen to evaluate for monoclonal gammopathy, tubular protein loss patterns, or other dysproteinemias. Specimen collection is performed in the outpatient phlebotomy/collection area or clinic restroom (for urine); the sample is labeled and transported to the clinical laboratory. A medical laboratory scientist performs electrophoresis, documents fractionation patterns, and generates a report including qualitative and quantitative interpretation for the ordering provider. Results are reviewed by the laboratory director when required and transmitted to the provider; the provider integrates findings with serum studies (if available), immunofixation, and clinical data to guide further testing or referral to hematology or nephrology.

Coding Specifications

Modifier	Description	When to Use
`26`	Professional component	When billing only the interpretive/professional component separate from the technical lab work, if applicable.
`TC`	Technical component	When billing only the technical component (laboratory processing) without the professional interpretation.
`90`	Reference (outside) laboratory	When the test is performed by an outside or reference laboratory under arrangement.
`91`	Repeat clinical diagnostic laboratory test	When a repeat test is performed on the same day to obtain subsequent results.
`52`	Reduced services	When the laboratory performs a reduced version of the test or limited portion of the procedure.
`59`	Distinct procedural service	When this electrophoresis is a distinct service from another lab procedure performed the same day on the same patient.
`76`	Repeat procedure by same physician or other qualified health care professional	When the same test is repeated by the performing laboratory (Note: `76` is not in the provided modifiers list; use `91` for repeats as provided.)
`22`	Increased procedural services	When the test requires substantially greater resources or time than usual, documented in the lab record.
`90`	Technical component performed by outside lab	When the specimen is sent out and only the ordering laboratory bills as an intermediary.
`95`	Synchronous telemedicine service rendered via a real-time interactive audio and video telecommunications system	Rarely applicable; use only if interpretation/consultation occurred via telehealth and billing rules permit.
`QW`	CLIA-waived test	Not typical for electrophoresis; include only if the method qualifies under CLIA waiver (unlikely).

Taxonomy Code	Specialty	Notes
207Q00000X	Clinical Pathology	Pathologists oversee and interpret electrophoresis results.
207L00000X	Clinical Laboratory	Medical laboratory scientists and directors perform and validate testing.
208M00000X	Hematology	Hematologists order and interpret electrophoresis in evaluation of gammopathies.
1835S0202X	Nephrology	Nephrologists order urine or other non-serum protein electrophoresis for kidney disease evaluation.

Related Diagnoses

ICD-10 Code	Description	Clinical Relevance
`N39.0`	Urinary tract infection, site not specified	UTI can cause proteinuria and may prompt urine protein fractionation to evaluate tubular vs glomerular loss.
`N18.9`	Chronic kidney disease, unspecified	CKD with proteinuria commonly leads to non-serum protein electrophoresis to characterize protein losses.
`R80.9`	Proteinuria, unspecified	Direct indication for urine protein electrophoresis to identify types and sources of proteinuria.
`D47.2`	Monoclonal gammopathy of undetermined significance (MGUS)	Electrophoresis on non-serum specimens may support evaluation when extramedullary or urinary monoclonal proteins are suspected.
`C90.00`	Multiple myeloma not having achieved remission	Used when evaluating for light-chain excretion or non-serum monoclonal proteins.

Related CPT Codes

CPT Code	Description	Relationship to This Procedure
`84166`	Electrophoresis; performed on specimen other than serum, separation and evaluation of protein fractions	The primary test for protein fractionation in non-serum specimens (urine, CSF, other body fluids).
`83036`	Protein; total, urine (e.g., 24-hour)	Often performed alongside `84166` to quantify total protein excretion prior to fractionation.
`82728`	Protein, electrophoresis, serum (e.g., SPEP)	Serum protein electrophoresis is commonly ordered in parallel to compare serum and non-serum profiles.
`83970`	Immunoglobulin, quantitative (IgG, IgA, IgM)	Performed when electrophoresis suggests monoclonal gammopathy to quantify immunoglobulin levels.
`86336`	Immunofixation; serum/urine, protein electrophoresis with immunofixation, any method	Used to identify specific monoclonal proteins following abnormal electrophoresis patterns.