Comorbidity measures are assigned using the AHRQ Elixhauser Comorbidity Software Refined for ICD-10-CM. The comorbidity measures identify pre-existing conditions (i.e., comorbidities) that are not directly related to the reason for the inpatient stay or the outpatient encounter. The 38 comorbidity measures are assigned using secondary ICD-10-CM diagnoses as follows:

• For 18 of the comorbidity measures, the assignment is based on whether the secondary diagnosis was present on admission (POA). The use of POA is necessary for conditions that could have arisen either prior to or during the hospital stay.
  • Some ICD-10-CM diagnosis codes are exempt from POA reporting because they are for circumstances regarding the healthcare encounter or factors influencing health status that do not represent a current disease or injury or that describe conditions that are always present on admission. When exempt codes are included in clinical criteria for a comorbidity measure that uses POA, the POA value of the code is not considered.
  • These 18 comorbidity measures are missing (.) on the HCUP databases that do not include POA information (HCUP data element DXPOAn). This includes all HCUP Nationwide databases and those HCUP State databases for which POA is unavailable.
• For the remaining 20 comorbidity measures do not use POA indicators because the condition can be assumed to be pre-existing and not the result of hospital care (e.g., diabetes, AIDS).

For more information, please refer to the Elixhauser Comorbidity Software Refined for ICD-10-CM page of the HCUP User Support website.

The availability of the comorbidity measures on the HCUP databases varies across data years:

• Starting in data year 2020, the measures from the Elixhauser Comorbidity Software Refined for ICD-10-CM are available on all HCUP databases, except the KID.
• For data year 2019, the measures from the Elixhauser Comorbidity Software Refined for ICD-10-CM are only available on the HCUP nationwide databases (except the KID).
• From data years 2016-2018, the comorbidity measures were not included on the HCUP databases because the ICD-10-CM version of the tool was considered in beta status.
• For data in the fourth quarter of 2015, the comorbidity measures (assigned by a preliminary beta version of the software) are stored in the data element I10_CM_aaa to indicate the implementation of the ICD-10-CM/PCS coding system.
• For data prior to the fourth quarter of 2015, the comorbidity measures are stored in the data element CM_ and are based on the ICD-9-CM coding system.