The Nationwide Readmissions Database (NRD) is part of a family of databases and software tools developed for the Healthcare Cost and Utilization Project (HCUP). The NRD addresses a large gap in healthcare data - the lack of nationally representative information on hospital readmissions for all patients, regardless of the expected payer for the hospital stay. The NRD is a unique and powerful database designed to support various types of analyses of national readmissions for all ages through data year 2022 and adult patients starting in data year 2023. Unweighted, the NRD contains data from approximately 13 to 17 million discharges each year. Weighted, it estimates roughly 28 to 35 million discharges. Developed through a Federal-State-Industry partnership sponsored by the Agency for Healthcare Research and Quality (AHRQ), HCUP data inform decision making at the national, State, and community levels.

This page provides an overview of the NRD. For more details, see NRD Database Documentation and the Introduction to the NRD, 2023 (PDF file, 1.12 MB) and prior years.

Contents:

• What's New in the 2023 AHRQ HCUP NRD?
• About the AHRQ HCUP NRD
• AHRQ HCUP NRD File Structure
• AHRQ HCUP NRD Data Elements
• Areas of Research and HCUP Publications
• Purchase the AHRQ HCUP NRD
• NRD Hardware and Software Requirements

Because of the limited availability of verified encrypted patient linkage numbers for pediatric patients, the NRD is limited to adult discharges (ages 18 years and older) starting in data year 2023.

Because of a change in the states available to participate in the 2023 NRD and a need to produce accurate national estimates, the following modifications have been made to the NRD:

• Limit the information released on patient characteristics:
  • Replace the data element identifying the detailed metropolitan status designation of the county of the patient’s residence (PL_NCHS) with a new consolidated data element that distinguishes only two categories: metropolitan and non-metropolitan (PL_NCHS2).
  • The data element for total hospital charge (TOTCHG) is replaced by the data element (TOTCHG_2023) that includes an adjusted total hospital charge that accounts for the hospital charges of discharges in missing states.
• Changes to the Diagnosis and Procedure Groups file:
  • Add data elements derived from the AHRQ HCUP Chronic Condition Indicator Refined (CCIR) for ICD-10-CM Diagnoses, v2024.1.
  • Use v2025.1 for all other AHRQ HCUP software tools included in the Diagnosis and Procedures Group file.

For more information on NRD data elements, see the NRD Description of Data Elements.

Please note that these modifications to the 2023 NRD may make comparisons of some estimates across years more difficult.

The NRD is a unique and powerful database designed to support various types of analyses of national readmissions for all patients, regardless of the expected payer for the hospital stay. The NRD includes discharges for patients with and without repeat hospital visits in a year and those who have died in the hospital. Repeat stays may or may not be related. The criteria to determine the relationship between hospital admissions are left to the analyst using the NRD. This database addresses a large gap in healthcare data - the lack of nationally representative information on hospital readmissions. Because of the limited availability of verified encrypted patient linkage numbers for pediatric patients, the NRD is limited to adult discharges (ages 18 years and older) starting in data year 2023.

The NRD is drawn from the HCUP State Inpatient Databases (SID) that contain verified encrypted patient linkage numbers that can be used to identify the inpatient stays for a patient across hospitals within a state, while adhering to strict privacy guidelines.

The NRD is designed to be flexible to various types of analyses of national readmissions. The criteria to determine the relationship between multiple hospital admissions for an individual patient are left to the analyst using the NRD. Outcomes of interest include national readmission rates, reasons for returning to the hospital for care, and the hospital costs for discharges with and without readmissions. The NRD is not designed to support regional, state-, or hospital-specific readmission analyses.

NRD data are available from 2010 through 2023, which allows researchers to analyze trends over time.

For more details on the 2023 NRD, see the Introduction to the NRD, 2023 (PDF file, 1.12 MB).

Information on previous years of the NRD may be found in prior years of the Introduction to the NRD at https://hcup-us.ahrq.gov/db/nation/nrd/nrdarchive.jsp.

The NRD is an annual, calendar-year file. There are three discharge-level files and one hospital-level file:

NRD Discharge-level Files

• Core File is a single discharge-level file containing commonly used data elements (e.g., age, expected primary payer, discharge status, ICD-10-CM/PCS codes, total charges).
  • The file is sorted by the NRD hospital identifier (HOSP_NRD) and the NRD unique record identifier (KEY_NRD). These two variables provide the linkage between the different discharge-level files.
• Severity File is a single discharge-level file containing additional data elements to aid in identifying the severity of the condition for a specific discharge.
  • The file is sorted by the NRD hospital identifier (HOSP_NRD) and the NRD unique record identifier (KEY_NRD).
• Diagnosis and Procedure Groups File is a single discharge-level file containing additional information on the ICD-10-CM diagnoses and ICD-10-PCS procedures created by the HCUP software tools.
  • The file is sorted by the NRD hospital identifier (HOSP_NRD) and the NRD unique record identifier (KEY_NRD).

NRD Hospital-level Files

• Hospital File is a single hospital-level file containing information on hospital characteristics.
  • The file is sorted by the NRD hospital identifier (HOSP_NRD).

Users interested in applying AHRQ HCUP software tools to the NRD for data years to produce data elements unavailable for specific data years may do so by downloading the respective tool(s) from the Research Tools section of the HCUP User Support (HCUP-US) website. Additionally, users may wish to review the AHRQ HCUP Software Tools Tutorial, which provides instructions on how to apply the software tools to HCUP or other administrative databases.

For 2015 data, because of the transition to ICD-10-CM/PCS on October 1, 2015, data elements related to diagnoses and procedures are included in files that are split into two parts. Nine months of the 2015 data with ICD-9-CM codes (discharges from January 1, 2015 - September 30, 2015) are in one set of files labeled Q1-Q3. Three months of 2015 data with ICD-10-CM/PCS codes (discharges from October 1, 2015 - December 31, 2015) are in a separate set of files labeled Q4. More information about the file structure changes for data year 2015 are included the document, 2015 Healthcare Cost and Utilization Project (HCUP) Nationwide Readmissions Database: Change in Structure and Data Elements Caused by Transition to ICD-10-CM/PCS.

The NRD contains clinical and nonclinical variables that support readmission analyses, with safeguards to protect the privacy of individual patients, physicians, and hospitals. There is no data element identifying whether sequential inpatient stays are related or unrelated. The criteria to determine the relationship between hospital admissions is left to the analyst using the NRD.

The NRD contains clinical and nonclinical data elements for each hospital stay. These include:

• Variables essential to readmission analyses
  • Verified encrypted patient linkage number that identifies discharges belonging to the same individual
  • Timing between admissions for a patient
  • Length of inpatient stay in days
  • Identification of transfers, same-day stays, and combined transfer records
  • Identification of the patient as a resident of the state in which he or she received hospital care
• Variables essential to calculating national estimates
  • Discharge weight for generating national estimates
  • Stratum used for weighting
• International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnosis, procedure, and external cause of injury codes prior to October 1, 2015
• International Classification of Diseases, Tenth Revision, Clinical Modification/Procedure Coding System (ICD-10-CM/PCS) diagnosis, procedures, and external cause of morbidity codes beginning October 1, 2015
• AHRQ HCUP software tools (with availability varying by data year)
• Patient demographic characteristics (e.g., sex, age, median household income for patient's ZIP Code, and urban-rural designation of the patient's county of residence)
• Expected primary payment source (e.g., Medicare, Medicaid, private insurance, self-pay, those billed as 'no charge', and other insurance types)
• Total hospital charges and hospital cost (cost can be calculated from total hospital charges using the Cost-to-Charge Ratio file that accompanies the NRD)

Beginning in data year 2016, the NRD includes diagnosis and procedure codes reported using only the ICD-10-CM/PCS coding system. The names of diagnosis- and procedure-related data elements under the ICD-10-CM/PCS coding system begin with the prefix "I10_" to identify the coding scheme.

Not all data elements are available for every year. For comprehensive information about the data elements and their availability by data year, see the NRD Description of Data Elements.

For information on modifications to the NRD data elements in data year 2023 due to changes in the participating states relative to prior years of the NRD, see the Introduction to the NRD, for 2023 (PDF) and the NRD Description of Data Elements.

As a uniform, multi-State weighted database, the NRD promotes comparative studies of healthcare services and supports healthcare policy and research on a variety of topics, including:

• National readmission rates by diagnosis, procedure, patient demographics, or expected payment source
• Costs associated with readmissions
• Reasons for readmissions
• Impact of health policy changes
• Readmissions by special populations.
HCUP Central Distributor. The NRD is used in a variety of publications and online tools:
• HCUP Statistical Briefs highlight a variety of health topics.
• Use the HCUP Publications Search Tool to find publications using the NRD.
• Review featured publications on the HCUP Research Spotlights page.
• HCUPnet is an online query system for identifying, tracking, analyzing, and comparing statistics on inpatient and outpatient care based on the HCUP databases.
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NRD releases data years 2010 through 2023 are available for purchase online through the AHRQ HCUP Central Distributor Online Reporting System (CDORS).

All HCUP data users, including data purchasers and collaborators, must complete the online AHRQ HCUP Data Use Agreement Training Tool, and read and sign the AHRQ HCUP Data Use Agreement for Nationwide Databases (PDF file, 260 KB; HTML).

Questions regarding the purchase or re-use of the data can be directed to the HCUP Central Distributor:

E-mail: HCUP-RequestData@ahrq.gov

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The NRD is distributed as comma-separated value (CSV) files delivered via secure digital download from the AHRQ HCUP Central Distributor Online Reporting System (CDORS). The files are compressed and encrypted with 7-Zip©. To load and analyze the NRD data on a computer, users will need the following:

• The password provided by the HCUP Central Distributor
• A hard drive with at least 205 gigabytes (GB) of space available
• A third-party zip utility such as ZIP Reader, 7-Zip© or WinZip®, SecureZIP®, WinZip®, or Stuffit Expander®. (The built-in utilities in Windows® and Macintosh® cannot decompress or decrypt these zip files and will produce an error message warning of incorrect password and/or file or folder errors.)
• SAS®, SPSS®, Stata® or similar analysis software

The data set includes weights for producing national estimates. NRD documentation and tools, including programs for loading the CSV files into SAS, SPSS, or Stata, are also available on the NRD Database Documentation page.

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