CPT code 88366: FISH interpretation, interpretation and report2026 Medicare rate & RVUs

Medicare pays $265.20 for 88366 nationally in the office. Local office rates run $233.05–$367.79.

Medicare allowed amount for participating (non-QP) physicians, before deductible, coinsurance and claim adjustments. Not a patient’s bill or a hospital charge.

What 88366 covers

A pathologist evaluates in situ hybridization findings, including fluorescent in situ hybridization (FISH) signals in tissue or cytology specimens, and prepares a diagnostic interpretation and report. Oncology specimens may be assessed for gene or chromosome changes relevant to tumor classification or treatment decisions. The report connects the probe findings with the specimen and clinical question; this service is distinct from performing the probe-staining procedure itself.

Report 88366 for the interpretation and report associated with an in situ hybridization study, supported by documentation identifying the specimen, test findings, and diagnostic conclusion. CMS recognizes professional and technical components: modifier 26 identifies the professional interpretation, modifier TC identifies the technical service, and billing without either modifier represents the global service. The professional component reflects the physician’s interpretation; the technical component covers equipment and staff involved in the test.

This summary was written with AI assistance from CMS physician fee schedule data and checked against the CMS billing rules shown here. Rates on this page come directly from CMS files.

Where 88366 pays more and less

The same RVUs, adjusted for each area’s costs. Open a locality for its calculation, history and nearby areas.

109 of 109 payment localities

88366 rates by state

Office rate range in each state. Select a state to see its payment localities.

How the 88366 rate is calculated

Each of 88366’s three RVUs is multiplied by a geographic index (GPCI) for the payment locality, added up, and multiplied by the conversion factor. Drag the indexes or enter a ZIP to see what moves the rate.

Payment rules and modifiers for 88366

The CMS indicators that decide how 88366 is paid alongside other services.

What modifiers do to the payment

When to use modifier 26

88366 compared with similar codes

How to choose

88364ISH probe stainEach additional probe

Use 88364 for the initial single-probe staining procedure. Use 88366 for interpretation and reporting of in situ hybridization findings.

88365In situ hybridizationManual probe stain

88365 describes an additional single-probe staining procedure; 88366 describes interpretation and reporting, not an additional stain.

88367ISH analysisAutomated morphometric analysis

88367 describes an automated in situ hybridization staining procedure. 88366 is the interpretation-and-report service.

88368ISH analysisManual, initial probe

88368 describes a manual in situ hybridization staining procedure. Choose 88366 for interpretation and reporting of the findings.

Codes related to 88366

Related codes aren’t interchangeable: bill the code that matches the service performed.

Where these rates come from

FeeBase calculates base physician payments from CMS work, practice-expense and malpractice RVUs, adjusted by each locality’s geographic indexes and the conversion factor. Services without a published rate are labeled, never given a made-up amount. Amounts are Medicare allowed amounts before claim adjustments: not a patient’s bill or a commercial rate.

CMS RVU26D · effective Oct 1, 2026 through the day before Jan 1, 2027

Open CMS sourceHow we calculate rates