ICD-11 Post-coordination
Build and read post-coordinated ICD-11 clusters. The inspector decomposes any cluster string in your browser; the challenges grade you against the same engine the platform's coding automation uses.
New to ICD-11? Read this first.
ICD-11 is not a new edition of ICD-10 — it is a different kind of thing, and almost nobody has used it yet. The Kosha explainer covers what it is, why it has a URI for every entity, and what post-coordination means, in about seven minutes.
Read the ICD-11 explainerICD-10 is a book that was digitised. ICD-11 is a web service that happens to have a book form — every entity has a URI, and a code can be composed from a stem plus extension codes. That makes ICD-11 competency a different skill from index-and-tabular lookup, which is why it cannot be taught from a book.
Cluster structure — separators, ordering, and whether a string round-trips — is checked in your browser, always. Whether a specific stem sanctions a specific axis is semantic: it lives in WHO's published data and is verified against the ICD-API, which the inspector will tell you it did or did not reach. Code tokens in the drills are supplied with each exercise and are not clinical guidance; the one real cluster (2C25.Z&XK8G&XA9HN5) is WHO's own worked example.
One condition, with detail added
A stem plus two extension codes. This is WHO's own published example.
Stem code
A stem code can stand on its own. It is the part you would have found in the tabular list, and every cluster begins with one. A cluster with no stem is malformed no matter what it means.
Two conditions in one cluster
Note which separator does which job — this is where most mistakes happen.
First stem
The primary condition. Stem order is meaningful — the first stem leads.
These labels describe each token's role in the grammar, not what the code means clinically. What a specific code denotes — and which axes a specific stem actually permits — lives in WHO's published data and is shown, with its title and URI, in the Cluster inspector.
Stem codes and extension codes
A stem code can stand on its own — it is what you would have found in the tabular list. Chapter X extension codes never stand alone; they add severity, anatomy, histopathology, an agent or a medicament to a stem. Post-coordination is the act of composing the two.
The two separators
"&" attaches an extension to the stem before it. "/" ends one stem group and starts the next. Stems always precede their extensions, so a cluster that opens with an X-code is malformed no matter what it means.
Why order must not matter
Two coders who pick the same extensions in a different sequence have coded the same thing. A system that compares raw strings would call them different, so clusters are normalised before they are compared — which is exactly what the inspector's canonical form shows.
Precoordination wins
Where a single category already expresses what you composed, that category must be used instead of the cluster. This is a rule about uniqueness: the same clinical meaning should not have two representations in the data.
For integrators — verifying server-side
The ICD-API's codeinfo endpoint decomposes a cluster string and returns which axes carry which values: GET /icd/release/11/{release}/mms/codeinfo/{cluster}. That is the same call that grades a learner here and that verifies an automatically-generated code — a machine-checkable correctness oracle ICD-10-CM never offered.
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Release-binding
ICD-11 ships annual releases, and a cluster valid under one may not be valid under another. Any stored code should carry the release it was built against — coded data that does not record this rots silently.
The full explainer
Foundation vs linearizations, the traditional-medicine chapters, and where ICD-11 sits next to SNOMED CT and ICD-10-CM.
Read the ICD-11 explainerICD-11 is published by the World Health Organization under CC BY-ND 3.0 IGO. Code titles are reproduced unaltered. HealthAtoms is not affiliated with, endorsed by, or acting on behalf of WHO.