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NASS Description of Data Elements

The following links provide data elements descriptions for the Nationwide Ambulatory Surgery Sample (NASS).

Data element descriptions explain how the data element is coded in the HCUP databases, what the uniform values are, and State-specific coding practices. The descriptions are cumulative across all States and years of NASS data from 2016 to the current data year. Please note the following:
  • Not all data elements in the NASS are uniformly coded across States. State-Specific notes are not available at this time.
  • Not all data elements in the NASS are available from every State.
The NASS is a calendar year file. All NASS data elements are listed in alphabetical order below, along with the file location for each data element.

For a description of how HCUP data elements are coded, and uniform values, check the corresponding boxes below and then click the "View Description of Data Elements".
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HCUP Data Element Descriptive Title Years File(s)
Data elements change frequently, and are only current as of the date generated.
Age in years at admission 2016-2019 Encounter
Admission month 2016-2019 Encounter
Admission day is on a weekend 2016-2019 Encounter
CMR_aaa Elixhauser Comorbidity Measure Refined for ICD-10-CM diagnosis codes 2019 DX_PR_GRPS
CMR_VERSION Version of the Elixhauser Comorbidity Measure Refined for ICD-10-CM diagnosis codes 2019 DX_PR_GRPS
CPT-4/HCPCS procedures 2016-2019 Encounter, Supplemental
Clinical Classifications Software (CCS): services and procedures classification 2016-2019 Encounter, Supplemental
Weight to discharges in the universe 2016-2019 Encounter, Hospital
Disposition of patient, uniform coding 2016-2018 Encounter
Discharge quarter 2016-2019 Encounter
Clinical Classifications Software Refined (CCSR): ICD-10-CM Diagnosis Classification within Body System AAA 2018-2019 DX_PR_GRPS
Default Clinical Classifications Software Refined (CCSR) for principal/first-listed ICD-10-CM diagnosis 2018-2019 DX_PR_GRPS
Version of the Clinical Classifications Software Refined (CCSR) for ICD-10-CM diagnosis codes 2018-2019 DX_PR_GRPS
Indicator of sex 2016-2019 Encounter
Hospital bedsize category 2016-2019 Hospital
Control/ownership of hospital 2016-2019 Hospital
Location (urban/rural) of hospital 2016-2019 Hospital
Location/teaching status of hospital 2016-2019 Hospital
NASS hospital number 2016-2019 Enncounter, Hospital, Supplemental, DX_PR_GRPS
Region of hospital 2016-2019 Hospital
Teaching status of hospital 2016-2019 Hospital
ICD-10-CM Diagnosis 2016-2018 Encounter
Injury ICD-10-CM diagnosis reported on record 2019 Encounter
Multiple ICD-10-CM injuries reported on record 2019 Encounter
Number of ICD-10-CM diagnoses on this discharge 2016-2019 Encounter
HCUP NASS record identifier 2016-2019 Encounter, Supplemental, DX_PR_GRPS
Number of universe discharges in the stratum 2016-2019 Hospital
Number of universe hospitals in the stratum 2016-2019 Hospital
NASS sample stratum 2016-2019 Hospital
Number of in-scope surgeries for this encounter 2016-2019 Encounter
Number of out-of-scope surgeries for this encounter 2016-2019 Supplemental
Expected primary payer, uniform 2016-2019 Encounter
Patient Location: NCHS Urban-Rural Code 2016-2019 Encounter
Race/ethnicity of patient 2019 Encounter
Number of discharges in the sample for the stratum 2016-2019 Hospital
Number of hospitals in the sample for the stratum 2016-2019 Hospital
AS encounters with at least one narrow surgery 2016-2019 Hospital
Total charges, cleaned 2016-2019 Encounter
Calendar year 2016-2019 Encounter, Hospital, Supplemental
Median household income for patient's ZIP Code (based on current year) 2016-2019 Encounter
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Internet Citation: NASS Description of Data Elements. Healthcare Cost and Utilization Project (HCUP). October 2021. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/db/nation/nass/nassdde.jsp.
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Last modified 10/14/21