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Trends in Inpatient Stays

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U.S. National: Overall Number of Inpatient Stays
Year All inpatient stays
2008 38,210,889
2009 37,734,584
2010 37,352,013
2011 36,962,415
2012 36,484,846
2013 35,597,792
2014 35,358,818
2015 35,769,942
2016 35,675,421
2017 35,798,453

Transition from ICD-9-CM to ICD-10-CM/PCS Coding

On October 1, 2015, the United States transitioned from ICD-9-CM1 to ICD-10-CM/PCS2. The graphics demarcate this transition with statistics reported using ICD-9-CM coding identified as "ICD-9-CM" on the graphs and statistics reported using ICD-10-CM/PCS coding identified as "ICD-10-CM/PCS" on the graphs. The 2015 rates of stays per 100,000 population and average statistics for hospitalization type in this section of HCUP Fast Stats are based on the first three quarters of data with ICD-9-CM codes only (January 1, 2015 to September 30, 2015). The number of inpatient stays by hospitalization type in 2015 is not reported because the statistics are not based on full year data. Statistics for all other characteristics include data for the full 2015 calendar year since these statistics are non-clinical, and therefore not impacted by the transition to ICD-10-CM/PCS. More information on the impact of ICD-10-CM/PCS is available on the HCUP User Support (HCUP-US) web page for ICD-10-CM/PCS Resources.

1 International Classification of Diseases, Ninth Revision, Clinical Modification
2 International Classification of Diseases, Tenth Revision, Clinical Modification/Procedure Coding System

Inpatient Stays

The national estimates presented in this section of Fast Stats are from the HCUP National (Nationwide) Inpatient Sample (NIS). The NIS is based on data from community hospitals, which are defined as short-term, non-Federal, general, and other hospitals, excluding hospital units of other institutions (e.g., prisons). The NIS includes obstetrics and gynecology, otolaryngology, orthopedic, cancer, pediatric, public, and academic medical hospitals. Excluded are community hospitals that are also long-term care facilities such as rehabilitation, psychiatric, and alcoholism and chemical dependency hospitals. Beginning in 2012, long-term acute care hospitals (LTACs) are also excluded from the sampling frame. However, if a patient received long-term care, rehabilitation, or treatment for psychiatric or chemical dependency conditions in a community hospital, the discharge record for that stay will be included in the NIS.

The NIS is sampled from the HCUP State Inpatient Databases (SID). Beginning with the 2012 data year, the NIS is a 20 percent sample of discharges from all community hospitals participating in HCUP in that data year. For data years 1988 through 2011, the NIS was a 20 percent sample of community hospitals and included all discharges within sampled hospitals. The national estimates presented in this section of Fast Stats were developed using the NIS Trend Weight Files for consistent estimates across all data years (e.g., LTACs were removed from analysis using trend weights).

Unit of Analysis

The unit of analysis in the NIS is the hospital discharge (i.e., the inpatient stay), not a person or patient. This means that a person who is admitted to the hospital multiple times in one year is counted each time as a separate discharge from the hospital. Counts are summarized by discharge year. There were no exclusions applied to the data (e.g., transfers to another acute care hospital are included as separate hospital stays).

Rate of Stays per 100,000

Population-based rates are presented for inpatient stay trends overall and by age, sex, community-level income, and hospitalization type. Rates are not reported by expected payer because currently there is no data source for national population insurance estimates that align with HCUP's definition of expected primary payer. The rate of stays includes the HCUP number of stays in the numerator and the U.S. resident population in the denominator (with a multiplier of 100,000). For age, sex, and community-level income, the denominator is consistently defined with the numerator (i.e., rates for females use HCUP counts and population counts specific to females). For hospitalization type, the denominator represents the total U.S. resident population. Population data are obtained from Claritas, a vendor that produces population estimates and projections based on data from the U.S. Census Bureau. Claritas estimates intercensal annual household and demographic statistics for geographic areas. Because of the transition from ICD-9-CM to ICD-10-CM/PCS on October 1, 2015, the 2015 rate of stays per 100,000 population for the hospitalization type characteristic is based on the first three quarters of 2015 data (Q1-3) only.

Cost per Stay

The NIS includes information on total hospital charges for an inpatient stay. Charges represent the amount a hospital billed for the entire hospital stay, excluding professional (physician) fees. Total hospital charges are converted to costs using HCUP Cost-to-Charge Ratios (CCRs) based on hospital accounting reports from the Centers for Medicare & Medicaid Services (CMS). Costs reflect the actual expenses incurred in the production of hospital services, such as wages, supplies, and utility costs. For each hospital in the NIS, a hospital-wide cost-to-charge ratio is used. The average cost per stay is calculated using discharges with nonmissing total costs. Costs are not imputed if total charges are not reported on the discharge record. Costs are only reported from 2000 forward because HCUP Cost-to-Charge Ratios are unavailable prior to 2000.

Inflation-Adjusted Cost per Stay

The actual average cost per stay is inflation adjusted using price indexes for the Gross Domestic Product (GDP) from the U.S. Department of Commerce Bureau of Economic Analysis (BEA). We used the BEA Interactive Data query tool to request National Data, GDP & Personal Income, Section 1 Domestic Product and Income, Table 1.1.4. Price Indexes for Gross Domestic Product. Price indexes for data years 19942014 were obtained on June 23, 2015. Price indexes for subsequent data years were obtained at later dates to coincide with updates to this section of Fast Stats. The adjustment used 2010 as the index base so that updates to the trends could retain a consistent base.

Length of Stay

The length of stay (LOS) is the number of days that the patient stayed in the hospital. It is calculated by subtracting the admission date from the discharge date. Same-day stays are therefore coded with a length of stay of 0. The average LOS is calculated using discharges with nonmissing LOS.

In-Hospital Mortality

In-hospital mortality is determined by the discharge disposition of the patient from the hospital. The numerator of the mortality rate is the number of patients within a reporting category (e.g., within a specific diagnosis category) who died in the hospital. The denominator is based on the total number of discharges in the reporting category. Discharges missing discharge disposition are excluded from the numerator and denominator of the in-hospital mortality rate.

Age

Age refers to the age of the patient at admission. Discharges missing age are excluded from results reported by age.

Sex

All nonmale, nonfemale responses are set to missing. Discharges with missing values for sex are excluded from results reported by sex.

Expected Payer

The "expected payer" data element in HCUP databases provides information on the type of payer that the hospital expects to be the source of payment for the hospital bill. Information is reported by the following expected primary payers: Medicare, Medicaid, private insurance, and self-pay/no charge. Patients identified as self-pay/no charge have an expected primary payer of self-pay, no charge, charity, or no expected payment. More information on expected payer coding in HCUP data is available in HCUP Methods Series Reports by Topic "User Guide - An Examination of Expected Payer Coding in HCUP Databases" (multiple documents; updated annually). Discharges missing expected payer are excluded from results reported by expected payer.

Discharges with the following expected primary payers are not reported in Fast Stats reporting for national trends in inpatient stays: other Federal, State, and local programs; missing; or invalid. In 2016, these excluded discharges represented 3 percent of all discharges.

The total reflecting the number of discharges across all expected payers (including those groups not presented in the graphs) is provided in the underlying data tables ("Show Underlying Data Tables") by expected payer. These totals are the same as the counts obtained for the all inpatient stays characteristic selection.

For comparison against the total described above for all expected payers, the Excel download file also provides the sum of the displayed expected payers (i.e., the sum of the expected payer counts of discharges across the expected payers that are displayed in the graphs).

Community-Level Income

Community-level income is based on the median household income of the patient's ZIP Code of residence. Quartiles are defined so that the total U.S. population is evenly distributed across four groups. Over time, the data element in the NIS for community-level income has changed definitions. Starting in data year 2002, the cut-offs for the quartile designation are determined annually using ZIP Code demographic data obtained from Claritas, a vendor that produces population estimates and projections based on data from the U.S. Census Bureau. Claritas estimates intercensal annual household and demographic statistics for geographic areas. The value ranges for the national income quartiles vary by year. Information by community-level income is only reported from 2002 forward because of inconsistent definitions over time in the income-related data elements in the NIS. Income quartile is missing if the patient is homeless or foreign. Discharges missing the income quartile are excluded from results reported by community-level income.

Hospitalization Type

Each discharge is assigned to a single hospitalization type hierarchically, based on the following order: maternal, neonatal, mental health/substance use, injury, surgical, and medical. All discharges are categorized in one of the six mutually exclusive hospitalization types based on the principal diagnosis for the hospital stay.

It should be noted that previously released statistics by hospitalization type for data year 2016 have been updated to use the definitions provided below for each of the six hospitalization types. In terms of the number of inpatient stays, the difference in the currently presented 2016 statistics versus previously presented 2016 statistics by hospitalization type are as follows:

  • Maternal: 0.3 percent higher
  • Neonatal: less than 0.01 percent lower
  • Mental Health/Substance Use: 14.4 percent lower
  • Injury: 3.4 percent lower
  • Surgical: 0.6 percent higher
  • Medical: 2.0 percent higher
The largest differences between previously released statistics and current statistics by hospitalization type for data year 2016 are for mental health/substance use. The new definition is based on Major Diagnostic Category (MDC) and, as a result, there are specific ICD-10-CM diagnosis codes that are no longer included. For example, discharges with a principal diagnosis code indicating alcoholic cirrhosis of the liver, Alzheimer's disease, and poisoning by narcotics and psychodysleptics are no longer assigned to the hospitalization type for mental health/substance use. The largest difference in prior versus current statistics for mental health/substance use in 2016 is for in-hospital mortality, which is 82.7 percent lower with the current statistics.

Maternal

Maternal discharges are defined using the following Clinical Classifications Software (CCS) for ICD-9-CM categories for data years 2015 and earlier or Major Diagnostic Category (MDC) beginning with data year 2016. MDC was assigned without using "present on admission" information on the record because not all HCUP data sources provide present on admission indicators.

  • Beginning with Data Year 2016: MDC 14, Pregnancy, Childbirth and the Puerperium
  • For Data Years 1994-2015: CCS 176-196
For data years 2015 and earlier, the CCS-based definition of maternal may result in slightly different counts of discharges when compared with other ways of classifying diagnosis codes. For example, compared with using MDC from 2015 and earlier, the CCS approach assigns 0.9 percent fewer cases to "maternal" because a maternal discharge is classified into a mental health CCS or a substance use CCS when the diagnosis code includes a mental health or substance abuse condition along with a maternal condition (e.g., drug dependence in pregnancy).

Neonatal

Neonatal discharges are defined using the following Clinical Classifications Software (CCS) for ICD-9-CM categories for data years 2015 and earlier or Major Diagnostic Category (MDC) beginning with data year 2016. MDC was assigned without using "present on admission" information on the record because not all HCUP data sources provide present on admission indicators.

  • Beginning with Data Year 2016: MDC 15, Newborns and Other Neonates with Conditions Originating in the Perinatal Period
  • For Data Years 1994-2015: CCS 218-224
For data years 2015 and earlier, the CCS-based definition of neonatal may result in slightly different counts of discharges when compared with other ways of classifying diagnosis codes. For example, compared with using MDC from 2015 and earlier, the CCS approach assigns 0.1 percent fewer cases to "neonatal" because a neonatal discharge is classified into a substance use CCS when the diagnosis code refers to a drug effect on the fetus or neonatal drug withdrawal.

Mental Health/Substance Use

Mental health/substance use discharges are defined using the following Clinical Classifications Software (CCS) for ICD-9-CM categories for data years 2015 and earlier or Major Diagnostic Category (MDC) beginning with data year 2016. MDCs were assigned without using "present on admission" information on the record because not all HCUP data sources provide present on admission indicators.

  • Beginning with Data Year 2016: MDC 19 and 20
  • For Data Years 2007-2015: CCS 650-663, 670
  • For Data Years 1994-2006: CCS 65-75

Injury

Injury discharges are identified by either: a) a principal diagnosis based on ranges of ICD-9-CM codes for data years 2015 and earlier, or b) a combination of the Clinical Classifications Software Refined (CCSR) for ICD-10-CM default categorization scheme for the principal diagnosis and individual ICD-10-CM diagnosis codes, for data years 2016 and later.

  • Beginning with Data Year 2016: CCSR INJ001-INJ027, INJ032 and ICD-10-CM diagnosis codes in the T84 series (used only for discharges from 1/1/2016-9/30/2016)
  • For Data Years 1994-2015: ICD-9-CM diagnosis codes 800-909.2, 909.4, 909.9, 910-994.9, 995.50-995.59, 995.80-995.85
The above definition of injury for data years 1994-2015 includes five ICD-9-CM diagnosis codes (965.00, 965.01, 965.02, 965.09, and 980.0) that are also included under two CCS diagnosis categories (660 and 661) used for the definition of the mental health/substance use hospitalization type for ICD-9-CM. Because of the hierarchical ordering used to assign discharges to hospitalization type, discharges with one of these five principal ICD-9-CM diagnosis codes are assigned to the mental health/substance use hospitalization type and not the injury hospitalization type.

Excluded Codes

It should be noted that ICD-9-CM and ICD-10-CM diagnosis codes related to complications of surgical or medical care, or adverse events or anaphylactic shock resulting from medication, anesthesia, or food are not used in the definition of the injury hospitalization type.

Surgical

Surgical discharges are identified by a surgical diagnosis-related group (DRG). The DRG grouper first assigns the discharge to a major diagnostic category (MDC) based on the principal diagnosis. For each MDC, there is a list of procedure codes that qualify as operating room procedures. If the discharge involves an operating room procedure, it is assigned to one of the surgical DRGs within the MDC category; otherwise it is assigned to a medical DRG. If the DRG indicates the information on the record is ungroupable (i.e., not identifiable as medical or surgical), then the discharge is assumed to be medical. This rarely occurs (less than 0.1 percent of total discharges).

Medical

Medical discharges are identified by a medical DRG. The DRG grouper first assigns the discharge to an MDC based on the principal diagnosis. For each MDC there is a list of procedure codes that qualify as operating room procedures. If the discharge involves an operating room procedure, it is assigned to one of the surgical DRGs within the MDC category; otherwise it is assigned to a medical DRG. If the DRG indicates the information on the record is ungroupable (i.e., not identifiable as medical or surgical), then the discharge is assumed to be medical. This rarely occurs (less than 0.1 percent of total discharges).

Use this export feature to download all of the underlying data for national trends in inpatient stays (all measures and characteristics) in Microsoft Excel (.xls) format.

  1. Select Excel Export to request the download.
  2. You must read and agree to the terms of the Data Use Agreement for HCUP Fast Stats that is displayed on the screen in order to obtain these data.
  3. Follow the prompts to save a copy of the Excel file to your computer. Prompting will vary by browser.
  4. If you decide to use these data for publishing purposes please refer to Requirements for Publishing with HCUP Data.


Internet Citation: HCUP Fast Stats. Healthcare Cost and Utilization Project (HCUP). May 2020. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/faststats/national/inpatienttrends.jsp.
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Last modified 5/26/2020