Observational Health Data Sciences and Informatics

ICD9CM, usually spelled “ICD-9-CM”, is a coding system in the USA, which is based on the WHO ICD9 coding system but has multiple additions and modifications.

The procedures for transforming Concepts from the source to the OMOP Standard Vocabularies can be found here.

All Concepts are assigned the longest of all available names.

All ICD9CM codes are represented in the format containing the dot. For example, the Concept for “Eating disorder, unspecified” is stored under the concept_code “307.50”.

All ICD9CM codes are non-Standard.

ICD9CM Concept Classes identify each Concept as part of the general coding scheme of diagnoses and disorders, the codes for health status and contact with health services (V codes, starting with the letter “V”) and those for external causes of injury (E codes, starting with the letter “E”). In addition, the Concept Classes distinguish between billing and non-billing codes. These are defined according to the Health Care Services Coding System of the Centers of Medicare and Medicaid Services (CMS). Billing codes are those that are used for reimbursement of services, while non-billing codes are Chapter, Category or Sub Category codes.

For each ICD9CM Concept, the Domain is inferred from the SNOMED Concept it is mapped to. If a ICD9CM Source Concept is mapped to more than one target SNOMED Concept, a combination Domain is assigned.

Please refer to Concepts of ICD-9-CM for details of the composition of this vocabulary.

There are types of relationships for ICD9CM: Mapping and hieararchical relationships.

These are recorded as “Maps to” relationships. These are manually curated based on input from UMLS (connection through common CUIs) and through MedDRA through ICD9CM to MedDRA maps in combination to MedDRA to SNOMED maps (see there).

For example, Concepts for history of, family history of, need for vaccination, etc. refer to observations that are recorded at a certain time, but the medical entity they are referring to, such as the disease for which family history is recorded, occurred at a different unspecified time earlier. These codes are mapped to SNOMED Observation Concepts using the “Maps to” relationship, and to the relevant medical entity to the “Maps to value” relationship. For example, ICD9CM 249.21 “Secondary diabetes mellitus with hyperosmolarity, uncontrolled” is mapped to Concept 195771 “Secondary diabetes mellitus” as well as 444369 “Hyperosmolality”. These multiple mappings can sometimes involve target Concepts of different domains. For example, ICD9CM 679.10 “Fetal complications from in utero procedure” is mapped to the Procedure 4043197 “Procedure on uterus” as well as the Condition 436489 “Complication of obstetrical surgery AND/OR procedure”.

These are constructed for those Concepts where the shorter code is entirely subsumed by longer one. Note that these relationships also exist between 3 and 5-digit codes according to these rules, which deviates from the preferred convention that “Subsumes” and “Is a” relationships only exist between directly related Concepts.

ICD9CM Concepts are non-Standard Concepts and therefore do not participate in the hierarchy of the OMOP Standardized Vocabularies CONCEPT_ANCESTOR table. However, the relationships between corresponding 3, 4 and 5-character Concepts exist as Concept Relationships in the CONCEPT_RELATIONSHIP table (see above).