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NIS Description of Data Elements
The National (Nationwide) Inpatient Sample (NIS) is a set of longitudinal hospital inpatient databases included in the HCUP family. These databases are created by AHRQ through a Federal-State-Industry partnership.
 

NIS Description of Data Elements
The following links provide data elements descriptions for the National (Nationwide) Inpatient Sample (NIS). Record layouts for the NIS files are available under File Specifications.

Data element descriptions explain how the data element is coded in the HCUP databases and what are the uniform values. The descriptions are cumulative across all years of NIS data from 1988 to the current data year. Please note the following:

  • Not all data elements in the NIS are uniformly coded across States. Please check the "State Specific Notes" section for each data element before analysis.
  • Not all data elements in the NIS are available from every State.
  • Not all data elements are available each year.

For certain data elements such as, but not limited to, patient race (RACE) and total charges (TOTCHG), more than one percent of NIS records have missing values. Users are advised to review frequencies for all data elements planned for use in their analysis and to consider analytic methods for dealing with missing data. The HCUP Methods Series Report #2015-01 provides guidance on alternative approaches to handling missing data in the NIS.

As a result of the introduction of ICD-10-CM/PCS1 on October 1, 2015 (quarter 4 of 2015 and the start of fiscal year 2016), the United States transitioned from using ICD-9-CM to ICD-10-CM/PCS code sets for reporting clinical diagnoses and inpatient procedures. Beginning with the quarter 4 of 2015, the names of diagnosis- and procedure-related data elements in the NIS start with the prefix "I10_" to identify the coding scheme. The coding change in 2015 also is signaled by a change in the NIS file structure:

  • The 2015 NIS included nine months of data with ICD-9-CM coding and three months of data with ICD-10-CM/PCS coding because of the mid-year change in diagnosis and procedure coding. The 2015 NIS files had a very different structure than other years and were split into two parts based on the diagnosis and procedure coding system.
  • Beginning with data year 2016, the NIS is an annual, calendar year file with diagnosis and procedure codes reported using only the ICD-10-CM/PCS coding system. Therefore, the file structure is similar to the file structure of the NIS in data years prior to 2015.

Data elements derived from AHRQ software tools which are based on ICD-10-CM/PCS diagnosis and/or procedure codes are not available on the NIS starting in quarter 4 of 2015. For users interested in applying the AHRQ software tools to the ICD-10-CM/PCS-coded data, the AHRQ software tools are available for download on the HCUP Tools & Software section of the HCUP User Support (HCUP-US) website. The Tools Loading tutorial is available to users interested in applying the AHRQ software tools at www.hcup-us.ahrq.gov/tech_assist/tutorials.jsp.

All NIS data elements are listed in alphabetical order below, showing the NIS file location for years other than 2015 and for 2015. For descriptions of HCUP data elements uniform values, check the corresponding boxes below and then click "View Description of Data Elements".

1 ICD-9-CM: International Classification of Diseases, Ninth Revision, Clinical Modification; ICD-10-CM/PCS: International Classification of Diseases, Tenth Revision, Clinical Modification/Procedure Coding System

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Abbreviations: DX, diagnosis; PR, procedure; Q1, discharge quarter 1; Q3, discharge quarter 3; Q4, discharge quarter 4.

HCUP Data Element Descriptive Title Years File(s) for years other than 2015 File(s) in 2015
Data elements change frequently, and are only current as of the date generated.
Admission day of week 1988-1997 Core  
Age in years at admission 1988-2017 Core Core
Neonatal age (first 28 days after birth) indicator 2012-2017 Core Core
Age in days (when AGE is less than 1 year) 1988-2011 Core  
AHA hospital identifier 1988-2011 Hospital  
Admission month 1988-2017 Core Core
All Patient Refined DRG 2002-2017 Severity Q1Q3 and Q4 Severity
All Patient Refined DRG: Risk of Mortality Subclass 2002-2017 Severity Q1Q3 and Q4 Severity
All Patient Refined DRG: Severity of Illness Subclass 2002-2017 Severity Q1Q3 and Q4 Severity
All-Payer Severity-adjusted DRG 2002-2009 Severity  
All-Payer Severity-adjusted DRG: Charge Weight 2002-2009 Severity  
All-Payer Severity-adjusted DRG: Length of Stay Weight 2002-2009 Severity  
All-Payer Severity-adjusted DRG: Mortality Weight 2002-2009 Severity  
Admission source, uniform coding 1988-2011 Core  
Admission source, as received from source 1988-2011 Core  
Admission source, (UB-92 standard coding) 2003-2011 Core  
Admission type 1988-2011 Core  
Admission day is on a weekend 1998-2017 Core Core
ICD-9-CM Body system n 2014-2015 Q3 Dx_Pr_Grps Q1Q3 Dx_Pr_Grps (not in Q4)
Clinical Classification Software (CCS) for Mental Health and Substance Abuse - General 2005-2006 Dx_Pr_Grps  
Clinical Classification Software (CCS) for Mental Health and Substance Abuse - Detail 2005-2006 Dx_Pr_Grps  
ICD-9-CM Chronic Condition Indicators 2005-2015 Q3 Dx_Pr_Grps Q1Q3 Dx_Pr_Grps (not in Q4)
Chronic Condition Indicators - body system 2005-2013 Dx_Pr_Grps  
AHRQ comorbidity measure for ICD-9-CM codes: acquired immune deficiency syndrome 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: alcohol abuse 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: deficiency anemias 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: rheumatoid arthritis/collagen vascular diseases 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: chronic blood loss anemia 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: congestive heart failure 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: chronic pulmonary disease 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: coagulopathy 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: depression 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: diabetes, uncomplicated 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: diabetes with chronic complications 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: drug abuse 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: hypertension (combine uncomplicated and complicated) 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: hypothyroidism 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: liver disease 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: lymphoma 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: fluid and electrolyte disorders 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: metastatic cancer 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: other neurological disorders 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: obesity 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: paralysis 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: peripheral vascular disorders 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: psychoses 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: pulmonary circulation disorders 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: renal failure 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: solid tumor without metastasis 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: peptic ulcer disease excluding bleeding 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: valvular disease 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
AHRQ comorbidity measure for ICD-9-CM codes: weight loss 2002-2015 Q3 Severity Q1Q3 Severity (not in Q4)
10% sample weight to discharges in the universe 1988-1997 Hospital  
Clinical Classifications Software: diagnosis classification 1988-1997 Core  
Died during hospitalization 1988-2017 Core Core
Weight to discharges in the universe 1998-2017 Core, Hospital Core, Hospital
Weight to discharges in frame states 1988-1997 Hospital  
Weight to discharges in state 1988-1997 Hospital  
Weight to discharges in universe 1988-1997 Hospital  
10% sample weight to discharges in the universe 1998-2004 Subsample  
Weight to discharges in the universe for national estimates of total charge in 2000. 2000 Core, Hospital  
10% sample weight to discharges in the universe for national estimates of total charge in 2000. 2000 Subsample  
Disposition of patient 1988-1997 Core  
Disposition of patient, UB04 standard coding 2007-2011 Core  
Disposition of patient, UB92 coding 1998-2006 Core  
Disposition of patient, uniform coding 1998-2017 Core Core
Discharge quarter 1988-2017 Core Core
Discharge quarter, as received from data source 2006-2011 Core  
DRG in use on discharge date 1988-2017 Core Q1Q3 and Q4 Dx_Pr_Grps
DRG in use on discharge date, calculated without POA 2008-2017 Core Q1Q3 and Q4 Dx_Pr_Grps
DRG, Version 10 1988-1999 Core  
DRG, Version 18 1998-2005 Core  
DRG, Version 24 2006-2014 Core  
DRG or MS-DRG grouper version used on discharge date 1988-2017 Core Q1Q3 and Q4 Dx_Pr_Grps
Disease Staging: Principal Disease Category 2002-2010 Severity  
Disease Staging: Length of Stay Level 2002-2007 Severity  
Disease Staging: Length of Stay Scale 2002-2007 Severity  
Disease Staging:Mortality Level 2002-2007 Severity  
Disease Staging: Mortality Scale 2002-2007 Severity  
Disease Staging: Resource Demand Level 2002-2007 Severity  
Disease Staging: Resource Demand Scale 2002-2007 Severity  
Disease Staging: Stage of Principal Disease Category 2002-2010 Severity  
Data source hospital number 1988-2011 Core  
Maximum number of diagnoses provided by source 1988-1997 Core  
Maximum number of procedures provided by source 1988-1997 Core  
Date source identification number 1988-1997 Core  
Data source type 1988-1997 Core  
ICD-9-CM Diagnosis 1988-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Clinical Classifications Software (CCS): ICD-9-CM diagnosis classification 1998-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Multi-Level CCS for ICD-9-CM Diagnoses 2009-2015 Q3 Dx_Pr_Grps Q1Q3 Dx_Pr_Grps (not in Q4)
Diagnosis coding system 1988-1997 Core  
Diagnosis codes ICD version indicator 2014-2017 Core Q1Q3 (not in Q4)
Diagnosis validity flag: Diagnosis n 1988-1997 Core  
Clinical Classifications Software (CCS) for ICD-9-CM External Cause of Injury Code 2003-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Multi-Level CCS for ICD-9-CM External Cause of Injury Code 2009-2015 Q3 Dx_Pr_Grps Q1Q3 Dx_Pr_Grps (not in Q4)
Clinical Classification Software (CCS) for Mental Health and Substance Abuse - General 2005-2006 Dx_Pr_Grps  
ICD-9-CM External Cause of Injury Code 2003-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Elective versus non-elective admission 2002-2017 Core Core
Indicator of sex 1998-2017 Core Core
Bedsize of hospital (definition used prior to 1998) 1993-1997 Hospital  
Control/ownership of hospital 1993-1997, 2008-2017 Hospital Hospital
Location of hospital (definition used prior to 1998) 1993-1997 Hospital  
Location/teaching status of hospital (definition used prior to 1998) 1993-1997 Hospital  
Hospital census region 1993-1997 Hospital  
Hospital teaching status (definition used prior to 1998) 1993-1997 Hospital  
HCUP indicator of emergency department record 2007-2017 Core Core
Hospital FIPS State/County code 2004-2011 Hospital  
Bedsize of hospital 1998-2017 Hospital Hospital
Control/ownership of hospital 1998-2011 Hospital  
Census Division of hospital (STRATA) 2012-2017 Core, Hospital Core, Hospital
Location (urban/rural) of hospital 1998-2011 Hospital  
Location/teaching status of hospital 1998-2017 Hospital Hospital
LPN FTEs per 1000 adjusted inpatient days 2007-2011 Hospital  
Multi-hospital system cluster code 2007-2011 Hospital  
Multi-hospital system membership 2007-2011 Hospital  
Nurse aides per 1000 adjusted inpatient days 2007-2011 Hospital  
NIS hospital number 2012-2017 Core, Hospital, Severity, Dx_Pr_Grps(Dx_Pr_Grps file not available in 2017) Core, Hospital, Q1Q3 and Q4 Severity, Q1Q3 and Q4 Dx_Pr_Grps
Percentage of all surgeries performed in the outpatient setting 2007-2011 Hospital  
Region of hospital 1998-2017 Hospital Hospital
RN FTEs per 1000 adjusted inpatient days 2007-2011 Hospital  
Percentage of RNs among all nurses (RNs and LPNs) 2007-2011 Hospital  
Teaching status of hospital 1998-2011 Hospital  
Hospital address from AHA Annual Survey 1993-2011 Hospital  
ICD-9-CM diagnosis indicates in-hospital birth 2006-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Hospital city from AHA Annual Survey 1993-2011 Hospital  
HCUP hospital identification number 1998-2011 Core, Hospital, Severity, Dx_Pr_Grps  
Hospital name from AHA Annual Survey 1993-2011 Hospital  
Hospital State postal code 1988-2011 Core, Hospital  
Hospital modified FIPS state/county code 1988-2011 Core (1988-2002), Hospital (2002-2011)  
Weight to hospitals in the universe 1998-2011 Hospital  
Weight to hospitals in the frame states 1988-1997 Hospital  
Weight to hospitals in the state 1988-1997 Hospital  
Weight to hospitals in the universe 1988-1997 Hospital  
Hospital zip code from AHA Annual Survey 1993-2011 Hospital  
ICD-10-CM Diagnosis 2015 Q4, 2016-2017 Core Q4 Dx_Pr_Grps
ICD-10-CM External Cause of Morbidity Code 2015 Q4, 2016 Core Q4 Dx_Pr_Grps
Number of ICD-10-CM diagnoses on this discharge 2015 Q4, 2016-2017 Core Q4 Dx_Pr_Grps
Number of ICD-10-CM External Cause of Morbidity codes on this record 2015 Q4, 2016 Core Q4 Dx_Pr_Grps
Number of ICD-10-PCS procedures on this discharge 2015 Q4, 2016-2017 Core Q4 Dx_Pr_Grps
ICD-10-PCS Procedure 2015 Q4, 2016-2017 Core Q4 Dx_Pr_Grps
Modified AHA hospital identifier 1988-2011 Hospital  
Unique record identifier 1998-2011 Core, Severity, Dx_Pr_Grps  
NIS record number 2012-2017 Core, Severity, Dx_Pr_Grps (Dx_Pr_Grps not available in 2017) Core, Q1Q3 and Q4 Severity, Q1Q3 and Q4 Dx_Pr_Grps
Hospital location and teaching status 1988-1992 Hospital  
Length of stay, cleaned 1988-2017 Core Core
Length of stay, as received from data source 1988-2011 Core  
MDC in effect on discharge date 1988-2017 Core Q1Q3 and Q4 Dx_Pr_Grps
MDC in use on discharge date, calculated without POA 2009-2017 Core Q1Q3 and Q4 Dx_Pr_Grps
MDC, Version 10 1988-1999 Core  
MDC, Version 18 1998-2005 Core  
MDC, Version 24 2006-2014 Core  
Synthetic attending physician number 1988-2000 Core  
Physician 1 number (re-identified) 2003-2009 Core  
Physician 1 number (synthetic) 2001-2002 Core  
Physician 2 number (re-identified) 2003-2009 Core  
Physician 2 number (synthetic) 2001-2002 Core  
Number of frame state discharges in STRATUM 1988-1997 Hospital  
Number of state's discharges in STRAT_ST 1988-1997 Hospital  
Number of discharges in the universe for the stratum 1988-2017 Hospital Hospital
Number of frame state hospitals in STRATUM 1988-1997 Hospital  
Number of state's hospitals in STRAT_ST 1988-1997 Hospital  
Number of hospitals in the universe for the stratum 1988-2017 Hospital Hospital
ICD-9-CM Number of chronic conditions 2008-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Number of ICD-9-CM diagnoses on this discharge 1988-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Number of ICD-9-CM External of Cause of Injury Codes on this Record 2003-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Neonatal and/or maternal ICD-9-CM DX and/or PR 1988-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Stratum used to post-stratify hospital 1998-2017 Core (2000+), Hospital Core, Hospital
Number of ICD-9-CM procedures on this discharge 1988-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Major operating room ICD-9-CM procedure indicator 2008-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Expected primary payer, uniform 1988-2017 Core Core
Expected primary payer, nonuniform 1988-1997 Core  
Expected primary payer, as received from data source 1998-2011 Core  
Expected secondary payer, uniform 1988-2011 Core  
Expected secondary payer, nonuniform 1988-1997 Core  
Expected secondary payer, as received from data source 1998-2011 Core  
Physician 1 number (synthetic) 1988-1997 Core  
ICD-9-CM Procedure class 2005-2015 Q3 Dx_Pr_Grps Q1Q3 Dx_Pr_Grps (not in Q4)
Patient Location: NCHS Urban-Rural Code 2013-2017 Core Core
Patient Location: NCHS Urban-Rural Code, 2006 2007-2012 Core  
Patient Location: Urban-Rural 4 Categories 2003-2006 Core  
Point of origin for admission or visit, UB04 standard coding 2007-2011 Core  
Point of origin for admission or visit, as received from source 2007-2011 Core  
ICD-9-CM Procedure 1988-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Clinical Classifications Software (CCS) for ICD-9-CM Procedures 1998-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Number of days from admission to procedure n 1988-2017 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Multi-Level CCS for ICD-9-CM Procedures 2009-2015 Q3 Dx_Pr_Grps Q1Q3 Dx_Pr_Grps (not in Q4)
HCUP processing identification record number 1988-1997 Core  
Procedure coding system 1988-1997 Core  
Procedure codes ICD version indicator 2015-2017 Core Not in Q4
Validity Flag: Procedure n 1988-1997 Core  
Race 1988-2017 Core Core
Number of sample discharges in STRAT_ST 1988-1997 Hospital  
Number of discharges in the sample for the stratum 1988-2017 Hospital Hospital
Number of sample hospitals in STRAT_ST 1988-1997 Hospital  
Number of hospitals in the sample for the stratum 1988-2017 Hospital Hospital
Sequence number 1988-1997 Core  
HCUP SID sequence number 1993-1997 Core  
Service line based on ICD-9 codes 2014-2015 Q3 Core Q1Q3 Dx_Pr_Grps (not in Q4)
Sex of the patient 1988-1997 Core  
Bedsize category 1988-1992 Hospital  
Ownership/control category 1988-1992 Hospital  
Hospital census region 1988-1992 Hospital  
Stratum for state-specific weights 1988-1997 Hospital  
Stratum used to post-stratify hospital 1988-1997 Hospital  
Synthetic primary surgeon number 1988-2000 Core  
Number of hospital discharges in the sample 1998-2017 Hospital Hospital
Total charges, cleaned 1988-2017 Core Core
Total charges, as received from data source 1988-2011 Core  
Total hospital discharges 1988-1997 Hospital  
Indicator of a transfer into the hospital 2008-2017 Core Core
Transfer out indicator 2010-2017 Core Core
Calendar year 1988-2017 Core, Hospital Core, Hospital
Median household income for patient's ZIP Code (based on 1999 demographics) 1998-2002 Core  
Median household income for patient's ZIP Code (based on current year) 2003-2017 Core Core
Median income for patient's ZIP Code (4 categories) 1988-1997 Core  
Median income for patient's ZIP Code (8 categories) 1988-1997 Core  

Abbreviations: DX, diagnosis; PR, procedure; Q1, discharge quarter 1; Q3, discharge quarter 3; Q4, discharge quarter 4.

*Beginning with 2017, external cause codes are at the end of the ICD-10-CM diagnosis array.

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Internet Citation: NIS Description of Data Elements. Healthcare Cost and Utilization Project (HCUP). August 2018. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/db/nation/nis/nisdde.jsp.
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Last modified 8/13/18