User Support

September 2013

Anne Pfuntner, Lauren M. Wier, M.P.H., and Carol Stocks, R.N., M.H.S.A.



Introduction

A patient can be admitted to the hospital with more than one medical condition. The principal diagnosis is the condition primarily responsible for the patient's admission. Hospitals need to know the most common principal diagnoses so that they can appropriately plan for and provide the resources required to treat patients with these more frequent conditions.

The Agency for Healthcare Research and Quality has provided an annual overview of national statistics on inpatient hospital stays, including principal diagnoses, since 2005. The statistics are based on data from the Healthcare Cost and Utilization Project (HCUP). The results from 2005 through 2009 are presented in a series of HCUP Facts and Figures reports.¹

The analysis of 2010 data on principal diagnoses was published in HCUP Statistical Brief #148, titled Most Frequent Conditions in U.S. Hospitals, 2010.² The present Statistical Brief analyzes 2011 data on the most common principal diagnoses for all hospital stays in the United States and covers stays by age and primary payer. The change in the number of stays and the rates of hospitalization in the population between 1997 and 2011 are also presented for the most common conditions. All differences between estimates noted in the text are statistically significant at the .001 level or better.

Findings

Most frequent principal diagnoses during hospital stays, 2011
Table 1 shows that there were 38.6 million hospital stays in 2011 in the United States (1,239 stays per 10,000 population). The 10 most frequent principal diagnoses listed in Table 1 accounted for 30 percent of all hospital stays.

The most common reason for hospitalization was liveborn (newborn infant), which accounted for 3.8 million stays in 2011 (10 percent of all stays).

Respiratory and circulatory conditions were among the 10 most common principal diagnoses in 2011. Two respiratory conditions—pneumonia and chronic obstructive pulmonary disease (COPD)—together accounted for 5 percent of all hospitalizations. Two circulatory conditions—congestive heart failure (CHF) and cardiac dysrhythmias—together accounted for another 5 percent of stays.

Osteoarthritis and spondylosis, both musculoskeletal conditions, were the fifth and tenth most frequent principal diagnoses, respectively, in 2011. A diagnosis of mood disorders, the only mental health diagnosis on the list, was the sixth most common condition and accounted for 896,000 stays in 2011.

Principal diagnoses with the most rapid growth, 1997–2011
Although the overall hospitalization rate in 2011 changed little from what it was in 1997, the rate increased sharply for some principal diagnoses (Table 2). Among the most common conditions for hospitalization, stays for acute renal failure experienced the most growth between 1997 and 2011, with the hospitalization rate increasing 346 percent (from 4 to 16 stays per 10,000 population). The hospitalization rate for five conditions—prolonged pregnancy, septicemia, pulmonary heart disease, osteoarthritis, and anemia—at least doubled during this period.

Most frequent principal diagnoses by age for hospital stays, 2011
Table 3 displays the five most frequent reasons for hospitalization by age group in 2011, as well as the change in the hospitalization rate for these diagnoses since 1997. The overall hospitalization rate increased with age with the exception of infants, whose high hospitalization rate (10,665 stays per 10,000 population) was driven largely by newborn births; these births accounted for 89 percent of stays for children who were younger than 1 year.

Among children aged 1–17 years, the diagnosis of mood disorders was the most common reason for hospitalization in 2011 (16 stays per 10,000 population). Asthma was the third most common condition among children aged 1–17 years in 2011, but the rate of hospitalization fell by nearly half since 1997 (from 24 to 13 stays per 10,000 population).

For adults aged 18–44 years, conditions related to pregnancy and childbirth accounted for four of the top five diagnoses in 2011: trauma to the perineum and vulva due to childbirth, delivery following a Cesarean section, prolonged pregnancy, and hypertension complicating pregnancy and childbirth. Together, these diagnoses accounted for 18 percent of stays among adults aged 18–44 years. Between 1997 and 2011, the hospitalization rate for delivery following a Cesarean section nearly doubled, and the rate for prolonged pregnancy nearly tripled. The hospitalization rate for normal pregnancy and/or delivery, however, fell 58 percent during this period (data not shown).

Among adults aged 45–64 years, musculoskeletal conditions—osteoarthritis and back problems (including spondylosis and disc disorders)—accounted for two of the five most frequent diagnoses in 2011. The hospitalization rate for osteoarthritis, the most common reason for hospitalization, grew by 160 percent between 1997 and 2011 (from 19 to 49 stays per 10,000 population). Osteoarthritis was also the most frequent principal diagnosis for adults aged 65–84 years, with the hospitalization rate increasing 54 percent since 1997.

Adults aged 65–84 years and aged 85 years and older shared four of the top five principal diagnoses: congestive heart failure (CHF), septicemia, pneumonia, and cardiac dysrhythmias. CHF was the most common reason for hospitalization for adults aged 85 years and older and the second most common reason for adults aged 65–84 years, but the hospitalization rate decreased for each of these age groups between 1997 and 2011 (18 percent and 31 percent, respectively).

Several principal diagnoses were common among multiple age groups in 2011. Pneumonia was a frequent condition among the youngest and oldest patients—children aged 17 years and younger and adults aged 65 years and older. The rate of hospitalization for pneumonia decreased in each of these age groups between 1997 and 2011. Septicemia was a common reason for hospitalization among adults aged 45 years and older. The overall hospitalization rate for septicemia increased rapidly between 1997 and 2011: 180 percent for adults aged 45–64 years, 104 percent for adults aged 65–84 years, and 74 percent for adults aged 85 years and older.

Hospital stays for septicemia among adults aged 45–64 years, 65–84 years, and 85 years and older, 1997 and 2011
One age-related finding of particular interest warranted additional analysis: septicemia had the most rapid growth in hospital stays per population between 1997 and 2011 among adults aged 45 years and older. Table 4 shows the number of stays and rate of hospitalization for the principal diagnoses that constitute septicemia, as listed in the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM).

Unspecified septicemia (septicemia NOS) accounted for the majority of septicemia hospitalizations (65–71 percent) within each of the age groups in 2011. The rate of hospitalization for unspecified septicemia increased six fold for adults aged 45–64 years, more than tripled for adults aged 65–84 years, and more than doubled for adults aged 85 years and older between 1997 and 2011.

Most frequent principal diagnoses by payer during hospital stays, 2011
Table 5 shows the five most frequent principal diagnoses for hospital stays by primary payer. Some of the most frequent diagnoses were specific to individual payers; however, other diagnoses were common among several primary payers.

Medicare was the primary payer for 15.3 million stays in 2011—an increase of 22 percent from 1997. Congestive heart failure (CHF) and septicemia were the most common principal diagnoses, each accounting for 5 percent of Medicare stays. The number of Medicare stays for septicemia more than doubled between 1997 and 2011. There was also an increase in the number of stays for cardiac dysrhythmias (41 percent) and osteoarthritis (88 percent) during this time period.

There were 7.6 million stays with Medicaid as the primary payer in 2011—a 34-percent increase since 1997. Conditions related to pregnancy and childbirth were three of the top five reasons for Medicaid stays: liveborn (newborn infant), trauma to the perineum and vulva caused by childbirth, and delivery following a Cesarean section. Together, these diagnoses accounted for 29 percent of Medicaid stays. The number of stays for delivery following a Cesarean section more than doubled between 1997 and 2011.

Private insurance was the primary payer for 12.2 million stays in 2011. The two most common reasons for stays billed to private insurance were related to pregnancy and childbirth: liveborn (newborn infant; 15 percent of stays) and trauma to the perineum and vulva caused by childbirth (3 percent of stays). The number of private insurance stays with osteoarthritis more than tripled since 1997.

The uninsured accounted for 2.1 million stays in 2011—an increase of 23 percent from 1997. Three of the most common conditions among uninsured hospital stays increased sharply between 1997 and 2011: mood disorders grew by 88 percent, diabetes mellitus with complications doubled, and stays for skin and subcutaneous tissue infections more than doubled.

Several principal diagnoses were common in stays across multiple primary payers. Liveborn (newborn infant) was the most common diagnosis for stays billed to Medicaid, private insurance, and the uninsured. The number of liveborn stays with Medicaid as the primary payer increased 39 percent between 1997 and 2011, but remained relatively stable for private insurance and uninsured stays. The diagnosis of mood disorders was also common for stays with a primary payer of Medicaid, private insurance, or the uninsured. Stays for mood disorders increased between 1997 and 2011 by 66 percent for Medicaid and 88 percent for the uninsured.

Data Source

The estimates in this Statistical Brief are based upon data from the Healthcare Cost and Utilization Project (HCUP) 2011 Nationwide Inpatient Sample (NIS). Historical data were drawn from the 1997 Nationwide Inpatient Sample (NIS). The statistics were generated from HCUPnet, a free, online query system that provides users with immediate access to the largest set of publicly available, all-payer national, regional, and State-level hospital care databases from HCUP. The Clinical Classifications Software (CCS) diagnosis categories for behavioral health (CCS 650–663 and 670), including Mood Disorders (CCS 657) and Alcohol-Related Disorders (CCS 660), were not available in HCUPnet for 1997; these statistics were separately calculated using the HCUP 1997 NIS. Supplemental sources included population denominator data for use with HCUP databases. ³

Many hypothesis tests were conducted for this Statistical Brief. Thus, to decrease the number of false-positive results, we reduced the significance level to .001 for individual tests.

Definitions

Diagnoses, ICD-9-CM, and Clinical Classifications Software (CCS)
The principal diagnosis is that condition established after study to be chiefly responsible for the patient's admission to the hospital. Secondary diagnoses are concomitant conditions that coexist at the time of admission or develop during the stay.

ICD-9-CM is the International Classification of Diseases, Ninth Revision, Clinical Modification, which assigns numeric codes to diagnoses. There are approximately 14,000 ICD-9-CM diagnosis codes.

CCS categorizes ICD-9-CM diagnoses into a manageable number of clinically meaningful categories.⁴ This "clinical grouper" makes it easier to quickly understand patterns of diagnoses. CCS categories identified as "Other" typically are not reported; these categories include miscellaneous, otherwise unclassifiable diagnoses that may be difficult to interpret as a group.

Case definition
The ICD-9-CM codes defining septicemia (except in labor) include diagnosis codes in the following range: 003.1, 036.2, 038.xx, 054.5, 449, 771.81, 790.7, 995.91, or 995.92.

Types of hospitals included in HCUP
HCUP 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). HCUP data include obstetrics and gynecology, otolaryngology, orthopedic, cancer, pediatric, public, and academic medical hospitals. Excluded are long-term care, rehabilitation, psychiatric, and alcoholism and chemical dependency hospitals. 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 Nationwide Inpatient Sample (NIS).

Unit of analysis
The unit of analysis is the hospital discharge (i.e., the hospital 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.

Payer
Payer is the expected primary payer for the hospital stay. To make coding uniform across all HCUP data sources, payer combines detailed categories into general groups:

• Medicare: includes patients covered by fee-for-service and managed care Medicare
• Medicaid: includes patients covered by fee-for-service and managed care Medicaid
• Private Insurance: includes Blue Cross, commercial carriers, and private health maintenance organizations (HMOs) and preferred provider organizations (PPOs)
• Other: includes Worker's Compensation, TRICARE/CHAMPUS, CHAMPVA, Title V, and other government programs
• Uninsured: includes an insurance status of "self-pay" and "no charge."

Encounters billed to the State Children's Health Insurance Program (SCHIP) may be classified as Medicaid, Private Insurance, or Other, depending on the structure of the State program. Because most State data do not identify SCHIP patients specifically, it is not possible to present this information separately.

When more than one payer is listed for a hospital discharge, the first-listed payer is used.

About HCUP

HCUP is a family of powerful healthcare databases, software tools, and products for advancing research. Sponsored by the Agency for Healthcare Research and Quality (AHRQ), HCUP includes the largest all-payer encounter-level collection of longitudinal healthcare data (inpatient, ambulatory surgery, and emergency department) in the United States, beginning in 1988. HCUP is a Federal-State-Industry Partnership that brings together the data collection efforts of many organizations—such as State data organizations, hospital associations, private data organizations, and the Federal government—to create a national information resource.

HCUP would not be possible without the contributions of the following data collection Partners from across the United States:

Alaska State Hospital and Nursing Home Association
Arizona Department of Health Services
Arkansas Department of Health
California Office of Statewide Health Planning and Development
Colorado Hospital Association
Connecticut Hospital Association
Florida Agency for Health Care Administration
Georgia Hospital Association
Hawaii Health Information Corporation
Illinois Department of Public Health
Indiana Hospital Association
Iowa Hospital Association
Kansas Hospital Association
Kentucky Cabinet for Health and Family Services
Louisiana Department of Health and Hospitals
Maine Health Data Organization
Maryland Health Services Cost Review Commission
Massachusetts Center for Health Information and Analysis
Michigan Health & Hospital Association
Minnesota Hospital Association
Mississippi Department of Health
Missouri Hospital Industry Data Institute
Montana MHA - An Association of Montana Health Care Providers
Nebraska Hospital Association
Nevada Department of Health and Human Services
New Hampshire Department of Health & Human Services
New Jersey Department of Health
New Mexico Department of Health
New York State Department of Health
North Carolina Department of Health and Human Services
North Dakota (data provided by the Minnesota Hospital Association)
Ohio Hospital Association
Oklahoma State Department of Health
Oregon Association of Hospitals and Health Systems
Oregon Health Policy and Research
Pennsylvania Health Care Cost Containment Council
Rhode Island Department of Health
South Carolina Budget & Control Board
South Dakota Association of Healthcare Organizations
Tennessee Hospital Association
Texas Department of State Health Services
Utah Department of Health
Vermont Association of Hospitals and Health Systems
Virginia Health Information
Washington State Department of Health
West Virginia Health Care Authority
Wisconsin Department of Health Services
Wyoming Hospital Association

About the NIS

The HCUP Nationwide Inpatient Sample (NIS) is a nationwide database of hospital inpatient stays. The NIS is nationally representative of all community hospitals (i.e., short-term, non-Federal, nonrehabilitation hospitals). The NIS is a sample of hospitals and includes all patients from each hospital, regardless of payer. It is drawn from a sampling frame that contains hospitals comprising more than 95 percent of all discharges in the United States. The vast size of the NIS allows the study of topics at both the national and regional levels for specific subgroups of patients. In addition, NIS data are standardized across years to facilitate ease of use.

About HCUPnet

HCUPnet is an online query system that offers instant access to the largest set of all-payer healthcare databases publicly available. HCUPnet has an easy step-by-step query system, allowing for tables and graphs to be generated on national and regional statistics as well as trends for community hospitals in the United States. HCUPnet generates statistics using data from HCUP's Nationwide Inpatient Sample (NIS), the Kids' Inpatient Database (KID), the Nationwide Emergency Department Sample (NEDS), the State Inpatient Databases (SID), and the State Emergency Department Databases (SEDD).

For More Information

For more information about HCUP, visit http://www.hcup-us.ahrq.gov/.

For additional HCUP statistics, visit HCUPnet, our interactive query system, at https://datatools.ahrq.gov/hcupnet.

For information on other hospitalizations in the United States, download HCUP Facts and Figures: Statistics on Hospital-Based Care in the United States in 2009, located at http://www.hcup-us.ahrq.gov/reports.jsp.

For a detailed description of HCUP, more information on the design of the Nationwide Inpatient Sample (NIS), and methods to calculate estimates, please refer to the following publications:

Introduction to the HCUP Nationwide Inpatient Sample, 2011. Online. June 2013. U.S. Agency for Healthcare Research and Quality. https://www.hcup-us.ahrq.gov/db/nation/nis/NIS_Introduction_2011.pdf. Accessed August 19, 2013.

Houchens R, Elixhauser A. Final Report on Calculating Nationwide Inpatient Sample (NIS) Variances, 2001. HCUP Methods Series Report #2003-2. Online. June 2005 (revised June 6, 2005). U.S. Agency for Healthcare Research and Quality. http://www.hcup-us.ahrq.gov/reports/methods/2003_02.pdf. Accessed August 19, 2013.

Houchens RL, Elixhauser A. Using the HCUP Nationwide Inpatient Sample to Estimate Trends. (Updated for 1988-2004). HCUP Methods Series Report #2006-05. Online. August 18, 2006. U.S. Agency for Healthcare Research and Quality. http://www.hcup-us.ahrq.gov/reports/methods/2006_05_NISTrendsReport_1988-2004.pdf. Accessed August 19, 2013.

Suggested Citation

Pfuntner A (Truven Health Analytics), Wier LM (Truven Health Analytics), Stocks C (AHRQ). Most Frequent Conditions in U.S. Hospitals, 2011. HCUP Statistical Brief #162. September 2013. Agency for Healthcare Research and Quality, Rockville, MD. http://www.hcup-us.ahrq.gov/reports/statbriefs/sb162.pdf.

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AHRQ welcomes questions and comments from readers of this publication who are interested in obtaining more information about access, cost, use, financing, and quality of healthcare in the United States. We also invite you to tell us how you are using this Statistical Brief and other HCUP data and tools, and to share suggestions on how HCUP products might be enhanced to further meet your needs. Please e-mail us at hcup@ahrq.gov or send a letter to the address below:

Irene Fraser, Ph.D., Director
Center for Delivery, Organization, and Markets
Agency for Healthcare Research and Quality
540 Gaither Road
Rockville, MD 20850



¹ Healthcare Cost and Utilization Project (HCUP). HCUP Facts and Figures. June 2013. Agency for Healthcare Research and Quality, Rockville, MD. http://www.hcup-us.ahrq.gov/reports/factsandfigures.jsp. Accessed August 19, 2013.
² Pfuntner A, Wier LM, Stocks C. Most Frequent Conditions in U.S. Hospitals, 2010. HCUP Statistical Brief #148. January 2013. Agency for Healthcare Research and Quality, Rockville, MD. http://www.hcup-us.ahrq.gov/reports/statbriefs/sb148.pdf. Accessed August 19, 2013.
³ Barrett M, Lopez-Gonzalez L, Coffey R, Levit K. Population Denominator Data for use with the HCUP Databases (Updated with 2012 Population data). HCUP Methods Series Report #2013-01. Online. March 8, 2013. U.S. Agency for Healthcare Research and Quality. http://www.hcup-us.ahrq.gov/reports/methods/2013_01.pdf. Accessed August 19, 2013.
⁴ HCUP Clinical Classifications Software (CCS). Healthcare Cost and Utilization Project (HCUP). U.S. Agency for Healthcare Research and Quality, Rockville, MD. Updated March 2013. http://www.hcup-us.ahrq.gov/toolssoftware/ccs/ccs.jsp. Accessed August 19, 2013.