# Practical Guide to Postcoordination

SNOMED CT is a global clinical terminology that represents medical concepts with unique identifiers. These concepts can be combined into expressions to capture complex clinical meanings.

A precoordinated expression includes a single concept. A postcoordinated expression combines multiple concepts based on SNOMED CT rules, allowing detailed clinical information to be recorded without creating a new concept for every possible detail.

Postcoordination enables richer EHR documentation, supports data sharing, natural language processing, and interoperability with other code systems. However, it requires careful implementation, skilled staff, and specialized tools.

To support postcoordination, EHR systems need to handle expressions just like standard SNOMED CT content. This also requires a terminology server that can store and process both regular SNOMED CT concepts and user-created expressions, linked to a specific SNOMED CT edition.

Terminology servers can offer different levels of support. At Level 0, only fully valid expressions are accepted. Level 1 allows slightly more flexibility. Currently, it’s advised to stick to Level 0 or 1 to ensure data quality, as higher-level support still needs further development.

<table data-view="cards"><thead><tr><th></th></tr></thead><tbody><tr><td><a href="introduction">Introduction</a></td></tr><tr><td><a href="https://github.com/SNOMED-Documents/snomed-postcoordination-guide/blob/main/broken-reference/README.md">SNOMED CT Expressions</a></td></tr><tr><td><a href="https://github.com/SNOMED-Documents/snomed-postcoordination-guide/blob/main/broken-reference/README.md">System Components</a></td></tr><tr><td><a href="https://github.com/SNOMED-Documents/snomed-postcoordination-guide/blob/main/broken-reference/README.md">Expressions in the EHR</a></td></tr><tr><td><a href="https://github.com/SNOMED-Documents/snomed-postcoordination-guide/blob/main/broken-reference/README.md">Expressions in a Terminology Server</a></td></tr><tr><td><a href="appendixes">Appendixes</a></td></tr></tbody></table>

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