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HCUP Fast Stats - Most Common Diagnoses for Inpatient Stays
HCUP Fast Stats provides easy access to the latest HCUP-based statistics for healthcare information topics. This section examines the most common conditions listed as the principal diagnosis for hospital inpatient stays by year, across a variety of patient characteristics.

Most Common Diagnoses for Inpatient Stays

Initial Selection:

Compare to:

2015* U.S. National Inpatient Stays: Age 0-17 Years
Maternal/Neonatal Stays Excluded
Rank Principal diagnosis Total number of stays Rate of stays per 100,000
1 Mood disorders * 157
2 Acute bronchitis * 131
3 Pneumonia (except that caused by tuberculosis or sexually transmitted disease) * 116
4 Asthma * 110
5 Epilepsy; convulsions * 89
6 Appendicitis and other appendiceal conditions * 68
7 Skin and subcutaneous tissue infections * 60
8 Fluid and electrolyte disorders * 57
9 Maintenance chemotherapy; radiotherapy * 52
10 Urinary tract infections * 42
Source: Agency for Healthcare Research and Quality (AHRQ), Healthcare Cost and Utilization Project (HCUP), National Inpatient Sample (NIS), 2015
*2015 Caution: Limited Reporting. See Data Notes & Methods.

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

2015 Caution: Limited Reporting

On October 1, 2015, the United States transitioned from ICD-9-CM1 to ICD-10-CM/PCS2. The 2015 rates of stays per 100,000 population 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 diagnosis in 2015 is not reported because the statistics are not based on full year data. 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.

2016 Data Not Available for Most Common Diagnoses

National statistics after 2015 are unavailable in this section of Fast Stats. The statistics for data prior to and including 2015 are based on the Clinical Classifications Software (CCS) for ICD-9-CM. The HCUP databases starting in 2016 only include diagnosis and procedure codes based on the ICD-10-CM/PCS coding scheme. The ICD-10-CM/PCS versions of the CCS are still under development. Users interested in obtaining similar statistics for 2016 data are encouraged to visit HCUPnet, our free online query tool.

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

Data Source

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).

Inpatient Stays

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 will be 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).


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


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 the uninsured. Uninsured discharges include records in which the expected primary payer was self-pay, charity, and no charge. Discharges for other types of payers (e.g., Workers' compensation, Indian Health Service, State and local programs) are not reported. 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.

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 compiles and adds value to 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.

Principal Diagnosis

The principal diagnosis is that condition established after study to be chiefly responsible for the patient's admission to the hospital. Diagnoses in the NIS are reported using ICD-9-CM codes through September 30, 2015 and ICD-10-CM codes beginning October 1, 2015. There are approximately 14,000 ICD-9-CM diagnosis codes and nearly 70,000 ICD-10-CM diagnosis codes. The Clinical Classifications Software (CCS) for ICD-9-CM and for ICD-10-CM categorizes ICD-9-CM and ICD-10-CM diagnosis codes into a manageable number of clinically meaningful categories, which may be more useful for presenting descriptive statistics and understanding patterns of diagnoses.

Results are reported by the CCS code of the principal diagnosis and list the top 10 most common principal diagnoses for each data year. The top 10 ranking is based on the weighted number of stays. Because of the transition from ICD-9-CM to ICD-10-CM/PCS on October 1, 2015, the total number of inpatient stays in 2015 is not reported. The 2015 rate of stays per 100,000 population is based on the first three quarters of 2015 data (Q1-3) only.

Results can be displayed with maternal and neonatal stays included or excluded from the ranking. This option is provided because maternal and neonatal discharges account for nearly a fourth of all hospital discharges in a year and the majority are low complexity, low cost stays. Maternal and neonatal stays are defined using the principal diagnosis CCS 176 through 196 for maternal and CCS 218 through 224 for neonatal.

Rate of Stays per 100,000

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). The denominator is consistently defined with the numerator (i.e., rates for females use HCUP counts and population counts specific to females). Population data are obtained from Claritas, a vendor that compiles and adds value to data from the U.S. Census Bureau. Claritas estimates intercensal annual household and demographic statistics for geographic areas. Rates are not reported by expected payer because payer-specific population denominators are not consistently available for the study period. Because of the transition from ICD-9-CM to ICD-10-CM/PCS on October 1, 2015, the rate of stays per 100,000 population is based on the first three quarters of 2015 data (Q1-3) only.

Use this export feature to download all of the underlying data for the most common diagnoses for national inpatient stays (for all characteristics every year) 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). December 2019. Agency for Healthcare Research and Quality, Rockville, MD.
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Last modified 12/12/2019