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ICD-11 Post-Coordinated Code Clusters

ICD-11 introduces some great new features, including post-coordinated codes. Though you may not use these terms, we’re all familiar with pre-coordinated codes since all of the codes in the code sets we use today (including ICD-10-CM, ICD-10-PCS and CPT for example) are pre-coordinated. Pre-coordinated codes contain the pertinent information about a clinical concept in a pre-combined fashion.

For the first time in ICD, the World Health Organization’s eleventh version for mortality and morbidity statistics (ICD-11 MMS) includes a mechanism to post-coordinate codes. Post-coordination is used to create “code clusters,” made up of codes linked together to fully describe a clinical condition. Codes are linked together in a cluster to add details and specificity. Post-coordination is used for example to specify anatomical location or additional manifestations or complications.

The table below presents two examples of post-coordinated code clusters in ICD-11 MMS compared to the single pre-coordinated ICD-10-CM code that reflects the same/similar level of detail.

Code assignment for: Osteoarthritis, right knee

ICD-11 MMS Post-Coordinated CodesICD-10-CM Pre-Coordinated Codes
FA01.Z Osteoarthritis of knee, unspecified
XK9K: Right
Code Cluster = FA01.Z & XK9K
M17.11: Unilateral primary osteoarthritis, right knee

Code assignment for: Diabetic ketoacidosis; Type 1 DM

ICD-11 MMS Post-Coordinated CodesICD-10-CM Pre-Coordinated Codes
5A22.0: Diabetic ketoacidosis without coma
5A10: [Has causing condition] Type 1 diabetes mellitus
Code Cluster = 5A22.0/5A10
E10.10: Type 1 diabetes mellitus with ketoacidosis without coma

In the first example, post-coordination in ICD-11 is used to link the extension code for “right” (XK9K) with the stem code for osteoarthritis of the knee (FA01.Z). Rather than creating an ICD-11 code for osteoarthritis of the knee with every possible laterality option (like we did in ICD-10-CM), ICD-11 has separate codes for laterality that are simply linked to the condition. So the ability to post-coordinate in ICD-11 provides a lot of flexibility without having to explode the code set with unique codes for all the possible combination codes.

The second example in the table demonstrates how post-coordination provides a mechanism to code diabetic manifestations. The ICD-10-CM code set includes over 300 codes for diabetes mellitus in order to specify combination codes for diabetes with all the various complications. In contrast, ICD-11 has one code for diabetes mellitus Type 1 and one code for Type 2. These two diabetes mellitus codes can be post-coordinated with the code for another condition to show diabetes as the cause of that condition.

The ability to post-coordinate codes helps keep the code set organized and provides a way to capture all the detail we need without exploding the code set with sometimes hundreds of additional codes to include every combination.