ICD10PCS, often spelled “ICD-10-PCS”, is a vocabulary in the USA for coding hospital-based medical procedures. It is currently implemented as a standard vocabulary, with OMOP-generated hierarchical relations to Procedure concepts from SNOMED CT vocabulary and other relationships mimicking SNOMED CT's internal model.
ICD10PCS concepts have up to 7 levels of hierarchy with the transition to each next level being represented by addition of one alphanumeric character to the parent concept's code. Only leaf-level concepts are billable and are allowed to be used in clinical setting and therefore are Standard concepts. Hierarchical levels 1 through 6 are always Classification concepts.
Classes for concepts in the ICD10PCS vocabulary are either 'ICD10PCS' for leaf-level concepts or 'ICD10PCS hierarchy' for preceding hierarchical levels.
Currently all concepts from the ICD10PCS Vocabulary belong to the Procedure domain. Some of them may relate to taking Measurements or administering Drugs in a clinical setting, but rely on other coding systems to specify important details (results of measurements or exact drug and dose that was administered). ICD10PCS concepts themselves still represent only the nature of actions performed by provider.
Leaf-level ICD10PCS concepts have custom relationships to SNOMED CT concepts. ICD10PCS procedures have attribute-value relationships built following SNOMED CT conventions to various SNOMED CT concepts that serve as attributes for concepts in procedure subhierarchy. Following the attribute assignment, hierarchical relationships are built to multiple SNOMED concepts, closest in meaning to ICD10PCS concepts themselves.
Due to differences in concept building between two vocabularies, complete match on attributes and meaning is never guaranteed even when concept names sound alike. Because of this, equivalence mappings are never built and all concepts remain Standard.
Internal ICD10PCS hierarchy is straightforward with each concept always having only one immediate ancestor. Leaf-level concepts also have multiple hierarchical relations to SNOMED CT concepts from procedure subhierarchy as terminal descendants. Both hierarchical trees exist in parallel.
Source files and coding guides at official CMS website;
Unified Medical Language System Primary data source for updates
SNOMED CT editorial guide: used to create attribute extensions and manage hierarchy