CPT 88366Laboratory

Insitu hybridization (fish)

CPT 88366 covers fluorescence in situ hybridization (FISH) testing, a specialized laboratory 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

$260.07

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

1.24

PE RVU (NF)

6.75

MP RVU

0.05

Total RVU

8.04

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

NCCI bundling edits

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Billing tips

Bill 88366 per probe set, not per specimen - if testing uses multiple different probe sets on the same specimen, each probe set may be separately billable
Impact: Can increase reimbursement from $260.07 to $520.14 or more when multiple distinct probe sets are medically necessary and properly documented
Document the specific gene or chromosome target for each FISH probe used (e.g., HER2, ALK, BCR-ABL, chromosome 17) in the pathology report
Impact: Prevents 15-20% of medical necessity denials and supports billing multiple units when applicable
Verify that diagnostic code supports medical necessity for the specific FISH test ordered - many payers have local coverage determinations limiting which diagnoses qualify
Impact: Reduces denial rate by 25-30%; common issue with screening versus diagnostic testing distinctions
For reflex FISH testing (performed automatically based on initial findings), ensure ordering physician documentation supports medical necessity before specimen analysis
Impact: Prevents $260.07 denial for tests performed without explicit order or medical indication
When billing with other pathology codes on same specimen, check NCCI edits carefully - 88366 may bundle with certain comprehensive cytogenetic codes
Impact: Avoids automatic claim rejections and reduces appeals; bundling errors cause 10-15% of initial denials
For Medicare patients, verify that FISH is performed for FDA-approved or compendia-listed indications to meet national coverage determination requirements
Impact: Ensures Medicare reimbursement eligibility; non-covered indications result in 100% payment denial ($260.07 loss)

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Frequently asked questions

What is the Medicare reimbursement rate for CPT code 88366 in 2025?

The 2025 Medicare national average payment rate for CPT 88366 is $260.07 for both facility and non-facility settings. This rate is based on 8.04 total RVUs (1.24 work RVU, 6.75 practice expense RVU, and 0.05 malpractice RVU) multiplied by the 2025 conversion factor of 32.3465.

Can you bill multiple units of 88366 on the same date of service?

Yes, you can bill multiple units of 88366 when different probe sets targeting distinct genetic markers are used on the same specimen, provided each is medically necessary and documented separately. Use modifier 59 or XU to indicate distinct services, and clearly document each specific probe and its clinical purpose to avoid bundling denials.

What is the difference between CPT 88366 and 88367 for FISH testing?

CPT 88366 covers the initial FISH probe, while 88367 is an add-on code for each additional FISH probe performed on the same specimen. Always bill 88366 first, then 88367 for subsequent probes. Both codes require distinct probe sets with separate clinical indications to justify billing.

Does CPT 88366 require a modifier 26 or TC for split billing?

Yes, modifier 26 (professional component) is used when billing only for the pathologist's interpretation, while modifier TC (technical component) is used when billing only for the laboratory work and reagents. Without a modifier, 88366 represents the global service including both components at the full $260.07 rate.

What diagnosis codes support medical necessity for CPT 88366?

Common supporting diagnoses include malignant neoplasms requiring HER2, ALK, or other biomarker testing (C50.x for breast cancer, C34.x for lung cancer), chronic myelogenous leukemia (C92.1x) for BCR-ABL testing, and specific genetic conditions. Check payer-specific LCDs as coverage varies by indication and gene target.

How many RVUs is CPT code 88366 worth in 2025?

CPT 88366 has 8.04 total RVUs in 2025, consisting of 1.24 work RVUs, 6.75 practice expense RVUs (both facility and non-facility), and 0.05 malpractice RVUs. This makes it one of the higher-valued laboratory procedure codes due to technical complexity and reagent costs.

Can CPT 88366 be billed with other cytogenetic codes like 88237 or 88261?

Billing 88366 with other cytogenetic codes requires careful NCCI edit checking. FISH (88366) is often separately billable from tissue culture (88237) and molecular cytogenetic studies (88271-88275), but may bundle with comprehensive chromosome analysis (88261-88264) unless modifier 59/XU is justified by distinct clinical purpose and documented accordingly.