Billing code 88366: FISH interpretationMedicare rate & RVUs in Washington
Reports the diagnostic interpretation of in situ hybridization findings, such as fluorescent probe results in tumor tissue, for a specific clinical question.
Medicare pays $277.25–$317.70 for 88366 in the office in Washington, from Rest Of Washington to Seattle (King Cnty). Which amount applies depends on the service address.
Medicare allowed amount for participating (non-QP) physicians, before deductible, coinsurance and claim adjustments. Not a patient’s bill or a hospital charge.
On this page 9 sections
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 in Washington
| Payment locality | Office | Facility |
|---|---|---|
| Rest Of Washington | $277.25 | Unavailable |
| Seattle (King Cnty) | $317.70 | Unavailable |
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.
How the rate is built · 88366
RVUs × geographic indexes × conversion factor
Work1.21
1.21 RVUs× 1.000 GPCI
Practice expense6.69
6.69 RVUs× 1.000 GPCI
Malpractice0.04
0.04 RVUs× 1.000 GPCI
Adjusted RVUs
7.9400
Conversion factor
$33.4009
Medicare rate
$265.20
Every GPCI starts at 1.000, the national rate. Enter a ZIP or drag a slider.
Payment rules and modifiers for 88366
The CMS indicators that decide how 88366 is paid alongside other services.
CMS payment indicators · 88366
FISH interpretation
| Rule | CMS value | What it means |
|---|---|---|
| Global period | XXX | The global surgery concept doesn’t apply. |
| Multiple procedures | 0 | No multiple-procedure reduction. |
| Bilateral (modifier 50) | 0 | The 150% bilateral adjustment doesn’t apply. |
| Assistant at surgery (80/81/82/AS) | 0 | Not paid without supporting documentation. |
| Co-surgeons (62) | 0 | Not permitted. |
| Team surgery (66) | 0 | Not permitted. |
| Professional/technical | 1 | Diagnostic test with separate professional (26) and technical (TC) components. |
What modifiers do to the payment
Modifier 26 · payment effect
With and without the modifier
88366 without 26 · national office
$265.20
FISH interpretation
88366-26 · Professional component
$57.78
Pays only the interpretation and report.
88366 compared with similar codes
Compare codes · National
5 codes, side by side
How to choose
- 88364ISH probe stain
- Use 88364 for the initial single-probe staining procedure. Use 88366 for interpretation and reporting of in situ hybridization findings.
- 88365In situ hybridization
- 88365 describes an additional single-probe staining procedure; 88366 describes interpretation and reporting, not an additional stain.
- 88367ISH analysis
- 88367 describes an automated in situ hybridization staining procedure. 88366 is the interpretation-and-report service.
- 88368ISH analysis
- 88368 describes a manual in situ hybridization staining procedure. Choose 88366 for interpretation and reporting of the findings.
88366 billing questions
How does 88366 differ from the probe-staining codes?
88366 represents interpretation and reporting of in situ hybridization findings. Codes such as 88364 and 88367 describe probe-staining procedures, including whether the procedure is automated.
Can the professional and technical portions be billed separately?
Yes. Modifier 26 identifies the professional interpretation and modifier TC identifies the technical service. Without either modifier, the claim represents the global service.
What documentation supports 88366?
The record should identify the specimen and in situ hybridization findings and include the diagnostic interpretation and report. The report should make clear the clinical conclusion drawn from the probe results.
Is 88366 reported for each probe?
The supplied CMS facts do not specify unit or probe-count instructions. Follow the applicable code-set unit guidance and document the interpreted study.
Is 88366 an add-on code?
The CMS facts supplied for this code do not identify add-on status or a required primary-code pairing.
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
Show the CMS file lines behind this rate
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