CPT 84181Laboratory

Western blot test

CPT code 84181 covers the Western blot test, a laboratory procedure that detects specific proteins in a blood or tissue sample. It's commonly used to confirm diagnoses of certain infections or diseases after initial screening tests.

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

Always link to a specific diagnosis code indicating the reason for confirmatory testing (e.g., positive screening result, suspected Lyme disease, HIV exposure)
Impact: Prevents medical necessity denials which account for approximately 35% of 84181 rejections; ensures full $17.14 reimbursement
Verify that initial screening test results are documented in the medical record before ordering Western blot
Impact: Payers frequently deny Western blot as first-line testing; documentation of prior screening can reduce denial rate by 40-50%
Bill only one unit per specimen per antigen tested; if testing for multiple distinct antigens, use modifier 59 and bill separately
Impact: Prevents downcoding from multiple units to single unit, protecting potential revenue of $17.14 per distinct antigen tested
Check LCD/NCD policies for specific conditions as many payers have coverage limitations on Western blot frequency (typically one confirmation per diagnosis episode)
Impact: Prevents denials for repeat testing; advance ABN collection when medically necessary repeat testing may not be covered
Ensure CLIA certificate number is current and high-complexity testing certification is active for the performing laboratory
Impact: Invalid CLIA certification results in 100% payment denial; verification prevents loss of entire $17.14 reimbursement
Submit claims within timely filing limits (typically 90-365 days depending on payer) and include ordering provider NPI
Impact: Late filing results in automatic denial regardless of medical necessity; ordering provider documentation required for most commercial payers

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Frequently asked questions

What is the Medicare reimbursement rate for CPT code 84181 in 2025?

The 2025 Medicare national average reimbursement rate for CPT code 84181 (Western blot test) is $17.14 for both facility and non-facility settings, based on 0.53 total RVUs and a conversion factor of 32.3465.

Can CPT 84181 be billed as a first-line screening test?

No, CPT 84181 should generally not be billed as a first-line screening test. Western blot is a confirmatory test typically performed after an initial screening test (like ELISA) yields positive or equivocal results. Billing as first-line testing often results in medical necessity denials.

How many RVUs is CPT code 84181 worth?

CPT code 84181 has a total RVU value of 0.53 for 2025, consisting of 0.37 work RVU, 0.15 practice expense RVU (both facility and non-facility), and 0.01 malpractice RVU.

What diagnosis codes support medical necessity for CPT 84181?

Common diagnosis codes supporting 84181 include those for suspected or confirmed Lyme disease (A69.20-A69.23), HIV exposure or positive screening (Z20.6, R75), autoimmune conditions requiring protein identification, and positive results from initial screening tests. The specific diagnosis must justify confirmatory testing.

Can multiple units of CPT 84181 be billed on the same day?

Yes, but only when testing for distinctly different antigens or proteins, requiring modifier 59 to indicate separate procedures. Multiple units for the same antigen on the same specimen are typically not separately reimbursable unless modifier 91 applies for medically necessary repeat testing.

What CLIA certification level is required to perform CPT 84181?

Western blot testing (CPT 84181) requires high-complexity CLIA certification. The laboratory must hold a valid CLIA certificate with high-complexity testing approval, and the test must be performed under the supervision of a qualified laboratory director.

Is CPT 84181 covered for Lyme disease confirmation?

Yes, CPT 84181 is widely covered for Lyme disease confirmation following a positive or equivocal ELISA or IFA screening test, consistent with CDC two-tiered testing recommendations. However, coverage requires documentation of the initial screening result and appropriate clinical indication.