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CMS & CDC GEM Files Bidirectional Mapping

ICD-9 to ICD-10 Crosswalk & GEM Mapping Tool

Translate legacy ICD-9 diagnostic codes into active ICD-10-CM codes, or convert ICD-10 back to ICD-9 for historical research, retrospective clinical studies, and payer audit reconciliations.

Popular: 401.9 → I10 (Hypertension) 250.00 → E11.9 (Type 2 Diabetes) 724.2 → M54.50 (Low Back Pain) 786.2 → R05.9 (Cough) V04.81 → Z23 (Immunization) I10 → 401.9 (Reverse)
Official GEM Crosswalk Result

Mapping for Code: 401.9

CMS GEM Source
Source Code (ICD-9) Target Code (ICD-10) Mapping Type No Map Flag Combination Flag
401.9 I10 → Exact Concept Match No (Valid Map) Single Target Code
Clinical Coding Guidance: While General Equivalence Mappings provide high accuracy baseline translations, ICD-10-CM offers vastly expanded clinical specificity (such as anatomical laterality, severity, and encounter status). Coders should always review the underlying medical record to select the most specific active ICD-10-CM code.

Understanding CMS General Equivalence Mappings (GEMs)

The Centers for Medicare & Medicaid Services (CMS) and the National Center for Health Statistics (NCHS) created the General Equivalence Mappings (GEMs) to serve as a comprehensive translation dictionary between ICD-9-CM and ICD-10-CM. GEMs are not simple crosswalk tables; they are translation matrices designed for:

  • Converting longitudinal clinical research databases across code revisions.
  • Auditing legacy claims and understanding retroactive coverage policy changes.
  • Assisting health plans in translating coverage payment policies from ICD-9 to ICD-10.

Because ICD-10 contains approximately 72,000 diagnostic codes compared to only 14,000 codes in ICD-9, many ICD-9 codes map to multiple possible ICD-10 codes depending on anatomical laterality (left, right, or bilateral) and encounter status.

Key GEM Flags Decoded

Approximate Flag (0 vs 1)

A value of 0 means the source and target codes represent the identical clinical concept. A value of 1 means the concepts are similar but not completely identical in clinical scope.

No Map Flag (0 vs 1)

A value of 1 indicates that the source code has no plausible equivalent concept in the target coding system, requiring independent medical review.

Combination Flag (0 vs 1)

A value of 1 indicates that the source code requires a combination of two or more target codes to accurately represent the complete clinical condition.