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ICD-10 R99 Conversion to ICD-9 798.0

ICD-10 to ICD-9 Crossover Result

ICD-10 Code R99 representing "Ill-defined and unknown cause of mortality" can be backward-mapped to its ICD-9 equivalent 798.0: "Sudden infant death synd". This conversion was generated using the latest General Equivalence Mappings (GEMs). While these mappings provide a standardized reference, not all ICD-10 codes have an exact ICD-9 match. Review the table below carefully and consider the clinical context when interpreting the mapped codes.

ICD‑10 Code

R99

Ill-defined and unknown cause of mortality

ICD‑9 Code

798.0

Sudden infant death synd

Approximate Flag – This ICD-10 code does not have an exact ICD-9 equivalent. The matched code is the closest available option and may not fully capture the original diagnosis.
ICD‑10 Code

R99

Ill-defined and unknown cause of mortality

ICD‑9 Code

799.9

Unkn cause morb/mort NEC

Approximate Flag – This ICD-10 code does not have an exact ICD-9 equivalent. The matched code is the closest available option and may not fully capture the original diagnosis.

About the General Equivalence Mappings Crossover Tool

The General Equivalence Mappings tool is a standardized crossover resource developed by the Centers for Medicare & Medicaid Services (CMS) and the National Center for Health Statistics (NCHS). It was created to help healthcare providers, coders, payers, and software vendors accurately transition between ICD-9 and ICD-10 diagnosis codes.

This ICD-10 to ICD-9 crosswalk tool supports both forward and backward mapping, making it valuable for converting legacy data, conducting audits, updating medical coding systems, and ensuring compliance with ICD-10 standards. GEMs are especially helpful when analyzing historical claims, aligning reimbursement logic, or migrating between systems.

Because not all ICD codes have a direct match, users should interpret each mapping carefully. Some ICD-10 to ICD-9 conversions may require clinical judgment or additional documentation to ensure coding accuracy. Not all ICD-10 to ICD-9 code conversions result in a single, exact match. In some cases, an ICD-10 code may map to multiple ICD-9 codes, especially when the original diagnosis requires more than one code to fully capture its meaning in the older coding system.