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ICD-11 Monthly – September 2023

Comparing Codes Across ICD Versions: Pneumonia, present on admission

By: Mary H. Stanfill, MBI, ACHIP, RHIA, CCS, CCS-P, FAHIMA

As the US has started exploring ICD-11 adoption, UASI is dedicated to looking for ways to make it’s adoption less intimidating. 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 for reporting healthcare services on claims in the US today.

In monthly code comparisons, we’ve looked at codes that are pre-coordinated or post-coordinated in ICD-11 and compared them with the most closely associated pre-coordinated ICD-10-CM codes. We’ve post-coordinated for example, complications or anatomical specificity with various conditions. This month we look at post-coordinating with ICD-11 extension codes that provide additional description about a diagnosis.

Let’s compare the codes for pneumonia, present on admission (POA), in both ICD-11 and ICD-10-CM.


  • These code assignments reflect the closest equivalent code from each code set as of August 2023.
  • Code category comparisons reflect excerpts from the ICD-11 MMS Browser compared to segments from the ICD-10-CM Tabular listing.
  • Only the codes in bold are complete (valid) codes. Nonbolded codes require additional characters.
  • The ICD-11 extension codes cannot be used alone, they must be post-coordinated with a stem code.

The table above shows various extension codes that can be post-coordinated with a pneumonia stem code in ICD-11. Much of the detail in these extension codes are not included in an ICD-10-CM pre-coordinated code. In the ICD-11 code assignment in this table, I only post-coordinated with the one extension code for POA, as that is the only additional detail I had. However, if I had more detail, the ICD-11 code cluster could be quite lengthy. For example, the code assignment for “bilateral idiopathic streptococcal pneumonia in an adult that is present on admission” in ICD-11 MMS is the following code cluster:

CA40.07 &XB5F&XK9J&XT65&XY6M

Does this lengthy code cluster look overwhelming? Production coders may be thinking “How will I find time to code all these details about every condition?” (At least, that’s what I’m thinking.) But then I remember that ICD-11 is a fully automated system. So, perhaps we don’t have to manually select an extension code for all of these details. Time in life could easily be automated based on the date of birth and date of encounter, for example. We don’t capture bilateral versus unilateral pneumonia now (in ICD-10-CM, “double” is a nonessential modifier). Perhaps that could be auto coded from the chest x-ray (it seems that would better reflect patient acuity). Those are just some ideas. But one thing is for sure, a move to ICD-11 will require not only integrating ICD-11 features and functions in encoder tools, but we’ll also need to consider EHR documentation practices, claims transaction standards, and data storage practices.

You can go to the WHO ICD-11 website to browse ICD-11 codes or review the WHO’s ICD-11 Implementation Guide. The Implementation Guide includes information on the digital format and advantages of ICD-11 for interoperability as well as implementation considerations.

Mary H. Stanfill is Vice President of Consulting for United Audit Systems, Inc. and is the official representative of the IFHIMA to the WHO Family of International Classifications 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.

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