CPT 88364Laboratory

Insitu hybridization (fish)

CPT 88364 covers fluorescence in situ hybridization (FISH) testing, a specialized lab technique that uses fluorescent probes to detect specific DNA sequences in tissue or cell samples to diagnose genetic abnormalities, cancers, and chromosomal disorders.

Showing rates for

National Average

Base Medicare rate

$125.18

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

0.7

PE RVU (NF)

3.15

MP RVU

0.02

Total RVU

3.87

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

NCCI bundling edits

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Billing tips

Bill each probe set separately with modifier 59 when using multiple distinct FISH probes on the same specimen for different genetic targets
Impact: Can increase reimbursement by $125.18 per additional probe set when properly documented with medical necessity; HER2 plus chromosome 17 enumeration commonly billed as two units
Document specific probe catalog numbers, target genes/chromosomes, and fluorophore colors in pathology report to support medical necessity
Impact: Reduces denial rate by approximately 35-40% by providing auditable evidence of distinct testing performed
Verify LCD/NCD coverage for specific FISH applications as Medicare has specific coverage criteria for HER2, ALK, and other molecular markers
Impact: Prevents denials on tests averaging $125.18; certain FISH tests require prior authorization or have limited coverage indications
Link appropriate ICD-10 diagnosis codes indicating malignancy or genetic condition requiring molecular characterization rather than screening codes
Impact: Medical necessity denials account for 25-30% of FISH claim rejections; proper diagnosis coding essential for payment
Bill 88364 per probe set analyzed, not per cell counted or slide prepared; ensure units billed reflect distinct molecular targets evaluated
Impact: Prevents upcoding audits and recoupment; overcoding units can trigger automated reviews and potential 3.87 RVU x excess units recoupment
Separate billing for FISH (88364) from other molecular pathology codes like PCR or microarray when both performed on same specimen with distinct clinical indications

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Frequently asked questions

What is the Medicare reimbursement rate for CPT 88364 in 2025?

The 2025 Medicare national average reimbursement for CPT 88364 is $125.18 for both facility and non-facility settings, based on 3.87 total RVUs and the 2025 conversion factor of 32.3465.

How many times can you bill CPT 88364 for the same patient specimen?

You can bill 88364 multiple times for the same specimen when using different FISH probe sets targeting distinct genetic markers, each with separate medical necessity. Use modifier 59 on additional units and document each probe's unique clinical purpose in the pathology report.

What is the difference between CPT 88364 and 88365?

CPT 88364 covers the initial FISH probe set analyzed on a specimen, while 88365 represents each additional FISH probe set on the same specimen. However, verify current CPT guidelines as coding structure may vary by payer regarding single versus multiple probe billing.

Does CPT 88364 include both technical and professional components?

Yes, CPT 88364 is a global code including both the technical laboratory work (3.15 PE RVUs) and professional interpretation (0.7 work RVUs). You can split billing using modifier 26 for professional component only or TC for technical component only when services are separated.

What diagnosis codes support medical necessity for CPT 88364?

Common supporting diagnoses include breast cancer (C50.x) for HER2 testing, chronic myeloid leukemia (C92.1) for BCR-ABL, multiple myeloma (C90.0) for chromosome deletions, and lung cancer (C34.x) for ALK rearrangements. The diagnosis must justify molecular characterization for treatment decisions.

Is prior authorization required for CPT 88364 FISH testing?

Prior authorization requirements vary by payer and specific FISH application. Many Medicare MACs do not require PA for established indications like HER2 in breast cancer, but commercial payers increasingly require authorization for high-cost molecular testing. Verify payer-specific policies before performing test.

How do you bill FISH testing performed by a reference laboratory?

When sending specimens to reference laboratories, the ordering facility typically bills with modifier 90 indicating outside laboratory performance, or the reference lab bills directly to the payer. Ensure clear financial arrangements and avoid duplicate billing. The interpreting pathologist's facility bills the global service or professional component only.