The WHO ICD-11 classification is very different from the 10th version that the United States modified to create the ICD-10-CM code set that is used in the US today. One key difference, ICD-11 post-coordinated code clusters, provides a flexible way to represent details about a condition.
Let’s compare codes for a common condition, diabetes mellitus, to illustrate this difference.
• These code assignments reflect the closest equivalent code from each code set as of May 2023.
• Code category comparisons reflect excerpts from the ICD-11 Browser compared to a segment from the ICD-10-CM Tabular listing.
The examples in the table above illustrate both pre-coordinated and post-coordinated codes for diabetes mellitus. Type 2 diabetes mellitus, without further specificity, is fully represented in one ICD-11 “stem” code (5A11). However, the ICD-11 code for diabetic ketoacidosis is post-coordinated to create a “code cluster” that fully reflects and links both conditions (5A22.0/5A11).
In ICD-11, two stem codes (which can standalone) can be post-coordinated using the “/” symbol. An ICD-11 stem code can also be post-coordinated with an extension code (which always starts with an X and cannot standalone), using the “&” symbol. (We saw the latter in the example last month with the extension codes for left or right post-coordinated with osteoarthritis.) The purpose of post-coordination is to link concepts about a condition to provide more details. In contrast, ICD-10-CM contains only pre-coordinated codes, which means every plausible combination of code details must be pre-defined in a combination code within the code set.
Post-coordination is an entirely new feature in the 11th version of ICD that provides flexibility and simplifies the data for data aggregation and use. It may not be simple however, to determine how to store, report, and archive the resultant code clusters. Note that, as with ICD-10-CM, clinical documentation must associate a complication with diabetes to post-coordinate the stem codes in a cluster. Note also, that ICD-11 does not assume unspecified diabetes mellitus is type 2, the type must be specified.
I’ll share additional features of ICD-11 and point out clinical documentation considerations in future blogs. So, stay tuned.
You can also go to the WHO website https://icd.who.int/en and use the ICD-11 coding tool to see a variety of “stem” codes and “extension” codes that can be post-coordinated together in a cluster.
Mary H. Stanfill is Vice President of Consulting for United Audit Systems, Inc. and is the representative of IFHIMA to the WHO Family of International Classifications (FIC) Education and Implementation (EIC) and Morbidity Reference Group (MbRG) workgroups. She has over 35 years of experience in the health information profession, primarily focused on clinical classification of healthcare data. She holds a masters in biomedical informatics and is currently pursuing a doctorate in health informatics.