CPT 88365Laboratory

Insitu hybridization (fish)

CPT code 88365 is for a specialized laboratory test called FISH (fluorescence in situ hybridization) that uses fluorescent markers to detect specific DNA sequences in tissue samples, often used to diagnose genetic abnormalities and cancers.

Showing rates for

National Average

Base Medicare rate

$168.85

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

0.88

PE RVU (NF)

4.31

MP RVU

0.03

Total RVU

5.22

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

NCCI bundling edits

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Billing tips

Bill each probe separately - each distinct FISH probe (HER2, BCR-ABL, etc.) constitutes a separate unit of 88365
Impact: Can increase reimbursement from $168.85 to $337.70+ when multiple probes medically necessary; append modifier 59 to second and subsequent probes
Document the specific probe and locus tested in pathology report (e.g., 'FISH for HER2/neu gene amplification, chromosome 17 centromere control')
Impact: Prevents 15-25% denial rate for inadequate specificity; required for medical necessity validation
Link to appropriate ICD-10 diagnosis code showing medical necessity - malignancy codes or suspected genetic abnormality codes required
Impact: Improves clean claim rate by 30%; screening codes without clinical indication result in denials
Verify LCD/NCD coverage for specific probe and indication - Medicare has specific coverage policies for FISH testing by cancer type
Impact: Prevents denials; some probe/indication combinations not covered, saving appeal costs averaging $150-300 per claim
For reflex FISH testing, document ordering physician's authorization if performed after initial pathology review
Impact: Reduces denial rate by 20% when FISH ordered as reflex test; requires ABN if Medicare may not cover
Separate date of service billing when FISH results finalized days after specimen collection - use date of interpretation
Impact: Ensures timely filing; FISH may take 3-7 days, affects claim submission deadlines

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Frequently asked questions

What is the Medicare reimbursement rate for CPT code 88365 in 2025?

The 2025 Medicare national average payment for CPT 88365 is $168.85 for both facility and non-facility settings, based on 5.22 total RVUs and the 2025 conversion factor of 32.3465.

Can I bill multiple units of 88365 for the same patient on the same day?

Yes, you can bill multiple units of 88365 when different FISH probes are used to test for distinct genetic targets (e.g., HER2 and chromosome 17 centromere). Append modifier 59 to the second and subsequent units and document each specific probe in the pathology report to avoid bundling denials.

What is the difference between CPT 88365 and 88364?

CPT 88365 is for in situ hybridization using fluorescence detection (FISH), while 88364 is for in situ hybridization using non-fluorescent methods (chromogenic detection). The methodology and detection system determine which code to use, not the clinical indication.

Does Medicare cover FISH testing for HER2 in breast cancer?

Yes, Medicare covers CPT 88365 for HER2 FISH testing in breast cancer patients when used to determine treatment eligibility for HER2-targeted therapies. Documentation must show malignancy diagnosis and clinical need for molecular characterization to guide treatment decisions.

What diagnosis codes support medical necessity for CPT 88365?

Medical necessity depends on the specific probe and clinical indication. Common supporting diagnoses include malignant neoplasms (C codes), suspected chromosomal abnormalities, abnormal tumor markers (R97.x), and specific cancer codes requiring molecular characterization. Screening codes without clinical symptoms typically result in denials.

How many RVUs is CPT code 88365 worth in 2025?

CPT 88365 has a total of 5.22 RVUs in 2025, comprising 0.88 work RVUs, 4.31 practice expense RVUs, and 0.03 malpractice RVUs. The PE RVU is the same for both facility and non-facility settings.

What are the CLIA requirements for billing CPT 88365?

CPT 88365 requires a CLIA certificate for high-complexity testing. The laboratory must meet personnel qualifications including a qualified laboratory director, and the test must be performed and interpreted under appropriate supervision. Moderate or waived CLIA certification is insufficient for FISH testing.