ICD-10 Code Converter¶

The ICD-10 converter maps diagnosis and procedure codes between fiscal year versions using CMS conversion tables. This lets you group claims coded in one year's ICD-10 version through a different year's MS-DRG grouper.

Why convert codes?¶

CMS updates ICD-10-CM and ICD-10-PCS codes every October 1 (the start of each federal fiscal year). Codes are added, deleted, split, and renamed. A claim coded with FY 2025 codes may not be recognized by the V43 (FY 2026) grouper, and vice versa.

Common scenarios:

• Backward mapping — a claim coded in FY 2026 that needs to be grouped with the V42 (FY 2025) grouper
• Forward mapping — a claim coded in FY 2025 that needs to be grouped with the V43 (FY 2026) grouper
• Cross-year analytics — comparing DRG assignments across fiscal years using consistent codes

How it works¶

graph LR
    A[Claim Codes<br>FY 2025] --> B[ICD Converter]
    B -->|"CMS conversion<br>table lookup"| C[Mapped Codes<br>FY 2026]
    C --> D[MS-DRG Grouper<br>V43]
    D --> E[DRG Assignment]

The converter uses CMS ICD-10 conversion tables which map each "current" code to its "previous" equivalent (and vice versa). At compile time, both directions are generated:

• Forward (newer → older): e.g., B8801 → B880
• Backward (older → newer): e.g., B880 → B8801

When a code has no mapping (most codes don't change year to year), the original code is returned unchanged.

Two ways to use it¶

1. Standalone converter¶

Call IcdConverter directly to map codes without grouping:

import msdrg

with msdrg.IcdConverter() as conv:
    new_code = conv.convert_dx("B880", source_year=2025, target_year=2026)
    # "B8801"

See Usage for full examples.

2. Automatic in the grouper¶

Set source_icd_version on a claim and the grouper converts codes before grouping:

with msdrg.MsdrgGrouper() as g:
    result = g.group({
        "version": 431,
        "source_icd_version": 2025,  # FY2025 codes → FY2026
        "pdx": {"code": "B880"},      # auto-converted to B8801
    })

result["conversions"]
# [{"original": "B880", "converted": "B8801", "code_type": "dx", "field": "pdx"}]

See Usage for full examples.

Data source¶

Conversion data comes from the CMS ICD-10-CM and ICD-10-PCS Conversion Tables, published annually at cms.gov. The tables are compiled into a single binary file per code type:

To regenerate the binary files from the latest CMS tables:

python scripts/compile_icd_conversions.py

Version to year mapping¶