Billing code 88365: In situ hybridizationMedicare rate & RVUs in Illinois
Reports a manual in situ hybridization probe stain, including FISH testing on tissue or cytology specimens to identify targeted genetic changes.
Medicare pays $157.46–$173.74 for 88365 in the office in Illinois, from Rest Of Illinois to Suburban Chicago. 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 88365 covers
This service covers laboratory staining and hybridization of a tissue or cytology specimen with a targeted nucleic acid probe. Fluorescence in situ hybridization (FISH) can help evaluate findings such as gene amplification or rearrangement in a tumor specimen. Pathology laboratories perform the technical work; a pathologist or other qualified professional may interpret the findings and report them. The code concerns the probe-staining procedure, not morphometric analysis of the resulting signals.
Select the code based on the documented probe-staining service performed on the specimen. The record should identify the specimen, probe or target, method, and findings supporting the test. CMS recognizes separately priced professional and technical components: report modifier 26 for interpretation and report, modifier TC for equipment and staff, or neither modifier when billing the global service.
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 88365 pays more and less in Illinois
The same RVUs, adjusted for each area’s costs. Open a locality for its calculation, history and nearby areas.
4 payment localities
$157.46 to $173.74
| Payment locality | Office | Facility |
|---|---|---|
| Chicago | $171.20 | Unavailable |
| East St. Louis | $158.88 | Unavailable |
| Rest Of Illinois | $157.46 | Unavailable |
| Suburban Chicago | $173.74 | Unavailable |
How the 88365 rate is calculated
Each of 88365’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 · 88365
RVUs × geographic indexes × conversion factor
Work0.86
0.86 RVUs× 1.000 GPCI
Practice expense4.17
4.17 RVUs× 1.000 GPCI
Malpractice0.03
0.03 RVUs× 1.000 GPCI
Adjusted RVUs
5.0600
Conversion factor
$33.4009
Medicare rate
$169.01
Every GPCI starts at 1.000, the national rate. Enter a ZIP or drag a slider.
Payment rules and modifiers for 88365
The CMS indicators that decide how 88365 is paid alongside other services.
CMS payment indicators · 88365
In situ hybridization
| 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
88365 without 26 · national office
$169.01
In situ hybridization
88365-26 · Professional component
$40.42
Pays only the interpretation and report.
88365 compared with similar codes
Compare codes · National
5 codes, side by side
How to choose
- 88364ISH probe stain
- 88364 is for the initial single-probe stain procedure on a specimen. Use 88365 for an additional single-probe stain procedure.
- 88366FISH interpretation
- 88366 reports the interpretation and report for in situ hybridization; 88365 represents probe-staining work.
- 88367ISH analysis
- 88367 describes manual morphometric analysis of in situ hybridization results, not the probe-staining procedure.
- 88368ISH analysis
- 88368 describes computer-assisted morphometric analysis of in situ hybridization results, rather than the stain procedure.
88365 billing questions
How does this differ from 88364?
Both codes are in the in situ hybridization family. 88364 represents the initial single-probe stain procedure; 88365 is used for an additional single-probe stain procedure on the specimen.
Can the professional and technical work be billed separately?
Yes. Modifier 26 identifies the professional interpretation and report, while modifier TC identifies the technical work, equipment, and staff. Without either modifier, the claim represents the global service.
Does this code include interpretation and reporting?
The professional component represents interpretation and reporting. Code 88366 is the separate in situ hybridization interpretation-and-report service when that code applies.
What should the laboratory document?
Document the specimen, probe or target, staining method, and the work performed. The pathology report should support the interpretation when the professional component is billed.
When would 88367 or 88368 be more appropriate?
Those codes describe morphometric analysis of in situ hybridization results, rather than the probe-staining procedure reported with 88365.
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
Fee sheets
Put 88365 and the rest of your codes on one sheet
Build a fee sheet from your own code list at your locality, put your payer contracts beside Medicare, and see what changed each quarter.
Build my fee sheetOr price your code list free →