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.

Table 1

Number of hospital stays and stays per 10,000 population by the most frequent principal diagnoses, 2011.

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.

Table 2

Number of hospital stays, stays per 10,000 population, and percentage change in rate, by selected principal diagnoses, 1997 and 2011.

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.

Table 3

Number of hospital stays, stays per 10,000 population, and percentage change in rate, by most frequent principal diagnoses and patient age, 1997 and 2011.

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).

Table 4

Number of hospital stays, stays per 10,000 population, and percentage change in rate of selected principal diagnoses for septicemia among adults aged 45–64 years, 65–84 years, and 85 years and older, 1997 and 2011.

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.

Table 5

Number of hospital stays, percentage distribution, and percentage change in stays by the most frequent principal diagnoses and payer, 1997 and 2011.

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.

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:

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Medicare: includes patients covered by fee-for-service and managed care Medicare

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Medicaid: includes patients covered by fee-for-service and managed care Medicaid

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Private Insurance: includes Blue Cross, commercial carriers, and private health maintenance organizations (HMOs) and preferred provider organizations (PPOs)

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Other: includes Worker's Compensation, TRICARE/CHAMPUS, CHAMPVA, Title V, and other government programs

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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.