CPT4 is a coding system for the reimbursement of ambulatory services in the US healthcare system provided by physicians. It represents Level I of the HCPCS system. Note: CPT4 is called Common Procedural Terminology, but it does not only contain medical procedures. CPT4 is copyright by the American Medical Association. Therefore CPT4 is licensed content and cannot be provided directly. The OHDSI vocabulary download contains only bare codes and relationships to actual OHDSI concepts. All additional information can only be retrieved by download using a UMLS account. For this purpose, a Java tool and respective instructions are provided within the vocabulary download.

All CPT4 codes are sourced from the NLM, as are maps from MeSH and relationships to LOINC. Relationships to SNOMED, such as ‘CPT-4 to SNOMED equivalent’, ‘CPT-4 to SNOMED category’, are sourced from UMLS Metathesaurus files.

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

All Concepts are assigned the longest of all available names whereas their Short Descriptions are stored as Synonyms.

All CPT4 codes are five-digits and can be either numeric or alphanumeric, depending on the category. Category I codes consist of 5 digits and Category II codes of 4 digits and a letter. Hierarchy entries come as a 7 digit code with a '10' as prefix. Modifier codes are two-digits.

By default, all CPT4 codes are standard, but in case of full semantic match they are mapped to Standard concepts in the respective domains, and become non-standard.

CPT4 section or subsection heading codes (CPT4 Hierarchy Concepts) are Classification Concepts.

Domains of CPT4 are currently assigned according to specific patterns, defined with help of regex expressions, and according to the domains of target standard concepts that the respective CPT4 concepts are mapped to. The latter approach has higher priority due to its accuracy.

Domain

Procedure

Measurement

Observation

Visit

Drug

Device

Spec Anatomic Site

Concepts are assigned a respective Concept Class as follows:

Source	Concept Class
CPT4 codes	CPT4
CPT4 modifiers	CPT4 Modifier
CPT4 section and subsection headings	CPT4 Hierarchy
CPT4 Place of Service	Visit

Relationships are defined as following:

1. There are “Is a” relationships from CPT4 Concepts and CPT4 Modifier Concepts to CPT4 Hierarchy Concepts

2. There are “Is a” relationships amongst CPT4 Hierarchy Concepts

3. There are “Is a” relationships between CPT4 Concepts that refer to other CPT4 Concepts. There are only a few relationships of this kind.

These relationships are defined as “CPT4 - LOINC eq” for various pathology and laboratory procedures. They were created by OHDSI and currently are not supported.

These relationships are defined as “CPT4 - SNOMED cat” and “CPT4 - SNOMED eq” for categorical (“uphill”) and equivalent relationships. These relationships are sourced from UMLS Metathesaurus and should be used only as reference.

By default, all valid CPT4 codes are Standard Concepts and therefore map to themselves. However, in case of full semantic match they are mapped to Standard concepts in the respective domains.

In CPT4, only vaccination procedures are recorded in sufficient detail so that the administered drug can be inferred. Other drug-related procedures, such as chemotherapies, are only mentioned as general procedures, without any specific drug product. The vaccine concepts lie between concept_codes 90281 and 90749. They are also descendants of the CPT4 hierarchical term 1012602 “Vaccines, Toxoids”.

One CPT4 vaccination code is mapped to RxNorm if it corresponds to one exact valid Drug Product in RxNorm.

The cases when CPT4 vaccine codes can’t be unambiguously mapped to RxNorm are provided below:

• More than one vaccine used for immunization against infections, but CPT4 does not distinguish them, e.g.:

concept_code	concept_name
90707	Measles, mumps and rubella virus vaccine (MMR), live, for subcutaneous use

• Influenza A viruses are very adaptable, and each year a new product is developed by the pharmaceutical industry for use during flu season. Therefore, the same CPT4 Concept may be mapped to different drugs depending on the year.
• Some CPT4 concepts are attributable to the historical vaccines that are no longer approved by FDA and no longer have a corresponding RxNorm code.
• Some vaccines against COVID-19 are not assigned RxNorm codes yet.

In these cases, we perform mapping to standard CVX codes.

CPT4 has a well-organized internal hierarchy of concepts. Meanwhile, CPT4 also contributes to the hierarchies of the Procedure, Measurement and Observation Domains. SNOMED/OMOP Extension provides the higher hierarchical concepts, while CPT4 are connected as descendants all the way down to leaf nodes. Hierarchical relationships between CPT4 and SNOMED/OMOP Extension are manually created.