Most Frequent Principal Diagnoses for Inpatient Stays in U.S. Hospitals, 2018

STATISTICAL BRIEF #277
July 2021

Kimberly W. McDermott, Ph.D., and Marc Roemer, M.S.


Introduction

Identifying the most frequent primary conditions for which patients are admitted to the hospital is important to the implementation and improvement of healthcare delivery, quality initiatives, and health policy. For example, this information can help establish national health priorities, initiatives, and action plans. Additionally, alternative payment models, such as hospital value-based purchasing programs, often focus on condition-specific metrics.1 At the hospital level, administrators can use diagnosis-related information to inform planning and resource allocation, such as optimizing subspecialty services or units for the care of high-priority conditions.

This Healthcare Cost and Utilization Project (HCUP) Statistical Brief presents statistics on the most frequent principal diagnoses among nonmaternal, nonneonatal inpatient stays using the 2018 National Inpatient Sample (NIS). First, the number of stays, mean cost per stay, and aggregate costs are presented for the most frequent principal diagnoses. Second, the distribution of stays for the most common diagnoses by select patient and hospital characteristics is shown. Finally, the top principal diagnoses by sex-age group are identified. Because of the large sample size of the NIS data, small differences can be statistically significant. Thus, only differences greater than or equal to 10 percent are discussed in the text.

Findings

Most frequent principal diagnoses among nonmaternal, nonneonatal inpatient stays, 2018
Figure 1 displays the aggregate cost of nonmaternal, nonneonatal inpatient stays for the 10 most frequent principal diagnoses in 2018, as indicated by the size of each circle. The mean cost per stay and total number of stays are shown on the y-axis and x-axis, respectively. Estimates of costs and number of stays are also reported in Table 1.
Highlights

Figure 1. Aggregate cost of nonmaternal, nonneonatal hospital inpatient stays, by mean cost and number of stays, 10 most frequent principal diagnoses, 2018

Figure 1 is a bubble chart that shows the aggregate cost of nonmaternal, nonneonatal inpatient stays for the 10 most frequent principal diagnoses in 2018, by mean cost and number of stays.

Abbreviation: B, billion; COPD, chronic obstructive pulmonary disease; ICD-10-CM, International Classification of Diseases, Tenth Revision, Clinical Modification
Notes: Diagnoses were identified using the Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. The pneumonia diagnosis group excludes pneumonia caused by tuberculosis.
Source: Agency for Healthcare Research and Quality (AHRQ), Healthcare Cost and Utilization Project (HCUP), National Inpatient Sample (NIS), 2018

Bubble chart that shows the aggregate cost of nonmaternal, nonneonatal inpatient stays for the 10 most frequent principal diagnoses in 2018, by mean cost and number of stays. Septicemia: no. of stays = 2,218,800; mean cost per stay = $18,700; aggregate costs =$41.5 billion. Heart failure: no. of stays = 1,135,900; mean cost per stay = $12,800; aggregate costs = $14.5 billion. Osteoarthritis: no. of stays = 1,128,100; mean cost per stay = $16,000; aggregate costs = $18.0 billion. Pneumonia: no. of stays = 740,700; mean cost per stay = $10,500; aggregate costs = $7.7 billion. Diabetes mellitus with complication: no. of stays = 678,600; mean cost per stay = $11,600; aggregate costs = $7.9 billion. Acute myocardial infarction: no. of stays = 658,600; mean cost per stay = $22,300; aggregate costs = $14.7 billion. Cardiac dysrhythmias: no. of stays = 620,000; mean cost per stay = $12,100; aggregate costs = $7.5 billion. COPD and bronchiectasis: no. of stays = 569,600; mean cost per stay = $9,200; aggregate costs = $5.3 billion. Acute and unspecified renal failure: no. of stays = 565,800; mean cost per stay = $9,600; aggregate costs = $5.4 billion. Cerebral infarction: no. of stays = 533,400; mean cost per stay = $14,900; aggregate costs = $7.9 billion.

  • Septicemia, the most common principal diagnosis among nonmaternal, nonneonatal stays in 2018, accounted for $41.5 billion in aggregate costs.

    Of the 10 most common principal diagnoses among nonmaternal, nonneonatal inpatient stays in 2018, septicemia was the most frequent and accounted for the highest aggregate costs ($41.5 billion). The mean cost per stay was also higher for septicemia than for the other top 10 conditions, with the exception of acute myocardial infarction (AMI).

    Osteoarthritis was the second most costly principal diagnosis among the top 10 diagnoses, with stays totaling $18.0 billion in aggregate costs. Of the 10 most frequent principal diagnoses, osteoarthritis ranked third in terms of both number of stays (after septicemia and heart failure) and mean cost per stay (after AMI and septicemia).

    Two circulatory conditions—heart failure and AMI—ranked in the top 10 principal diagnoses in 2018 and accounted for $14.5 and $14.7 billion in aggregate costs, respectively. Compared with stays for heart failure, stays for AMI were far less common but more expensive on average.
Table 1 presents the 20 most frequent principal diagnoses among nonmaternal, nonneonatal inpatient stays in 2018. Total number of stays, aggregate cost, and mean cost per stay are provided for each diagnosis.

Table 1. Top 20 principal diagnoses among nonmaternal, nonneonatal inpatient stays, 2018
Rank Principal diagnosis Number of stays Percent of stays Aggregate cost, $ billions Percent of aggregate cost Mean cost per stay, $
All nonmaternal/nonneonatal stays 27,833,500 100.0 403.6 100.0 14,500
Top 20 diagnoses 13,236,300 47.6 188.3 46.7 14,200
1 Septicemia 2,218,800 8.0 41.5 10.3 18,700
2 Heart failure 1,135,900 4.1 14.5 3.6 12,800
3 Osteoarthritis 1,128,100 4.1 18.0 4.5 16,000
4 Pneumonia (except that caused by tuberculosis) 740,700 2.7 7.7 1.9 10,500
5 Diabetes mellitus with complication 678,600 2.4 7.9 1.9 11,600
6 Acute myocardial infarction 658,600 2.4 14.7 3.6 22,300
7 Cardiac dysrhythmias 620,000 2.2 7.5 1.9 12,100
8 COPD and bronchiectasis 569,600 2.0 5.3 1.3 9,200
9 Acute and unspecified renal failure 565,800 2.0 5.4 1.3 9,600
10 Cerebral infarction 533,400 1.9 7.9 2.0 14,900
11 Skin and subcutaneous tissue infections 529,600 1.9 4.0 1.0 7,600
12 Depressive disorders 525,000 1.9 2.8 0.7 5,400
13 Spondylopathies/Spondyloarthropathy 519,600 1.9 12.5 3.1 24,000
14 Urinary tract infections 508,700 1.8 3.8 0.9 7,500
15 Respiratory failure; insufficiency; arrest 506,800 1.8 9.1 2.2 17,900
16 Schizophrenia spectrum and other psychotic disorders 399,900 1.4 3.7 0.9 9,300
17 Coronary atherosclerosis and other heart disease 358,900 1.3 8.7 2.2 24,400
18 Biliary tract disease 349,900 1.3 4.5 1.1 13,000
19 Fluid and electrolyte disorders 349,800 1.3 2.7 0.7 7,600
20 Complication of select surgical or medical care, injury, initial encounter* 338,800 1.2 6.0 1.5 17,700
Abbreviations: COPD, chronic obstructive pulmonary disease; ICD-10-CM, International Classification of Diseases, Tenth Revision, Clinical Modification
Notes: Diagnoses were identified using the Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Number of stays is rounded to the nearest hundred. Mean cost per stay is rounded to the nearest $100.
* This includes complications, such as infection, for surgical or medical care other than those from cardiovascular, genitourinary, or internal orthopedic devices or from organ/tissue transplants.
Source: Agency for Healthcare Research and Quality (AHRQ), Healthcare Cost and Utilization Project (HCUP), National Inpatient Sample (NIS), 2018

  • The top 20 principal diagnoses constituted nearly half of all nonmaternal, nonneonatal inpatient stays and nearly half of aggregate costs for these stays in 2018.

    In 2018, there were 27,833,500 nonmaternal, nonneonatal hospital stays in the United States. The 20 most frequent principal diagnoses accounted for 47.6 percent of these stays (13,236,300 stays) and 46.7 percent of aggregate costs for these stays ($188.3 billion).


  • Septicemia accounted for 8 percent of all nonmaternal, nonneonatal stays in 2018. Heart failure and osteoarthritis each accounted for 4 percent.

    Inpatient stays with a principal diagnosis of septicemia accounted for 8.0 percent of all nonmaternal, nonneonatal stays (2,218,800 stays) and 10.3 percent of aggregate costs for these stays ($41.5 billion).

    Five circulatory conditions were among the 20 most common principal diagnoses in 2018: heart failure (1,135,900 stays; $14.5 billion in aggregate costs), AMI (658,600 stays; $14.7 billion), cardiac dysrhythmias (620,000 stays; $7.5 billion), cerebral infarction (533,400 stays; $7.9 billion), and coronary atherosclerosis and other heart disease (358,900 stays; $8.7 billion). Combined, these diagnoses accounted for 11.9 percent of stays and 13.2 percent of aggregate costs. Stays for two of these circulatory diagnoses—coronary atherosclerosis and other heart disease, and AMI—were relatively expensive compared with most other top diagnoses, averaging more than $20,000 per stay.

    Three respiratory diagnoses were also among the top 20 principal diagnoses: pneumonia (740,700 stays; $7.7 billion in aggregate costs), COPD and bronchiectasis (569,600 stays; $5.3 billion), and respiratory failure, insufficiency, or arrest (506,800 stays; $9.1 billion). Together, these diagnoses constituted 6.5 percent of stays and 5.5 percent of aggregate costs. The average cost of stays for respiratory failure, insufficiency, or arrest was relatively high compared with stays for pneumonia and stays for COPD and bronchiectasis ($17,900 vs. $10,500 and $9,200, respectively).

    The two musculoskeletal diagnoses in the top 20 rankings—osteoarthritis (1,128,100 stays; $18.0 billion in aggregate costs) and spondylopathies/spondyloarthropathy (519,600 stays; $12.5 billion)—made up 5.9 percent of stays and 7.6 percent of aggregate costs. Of these two principal diagnoses, osteoarthritis was far more common, accounting for more than twice as many stays as spondylopathies/spondyloarthropathy. However, on average, stays for spondylopathies/ spondyloarthropathy were more expensive than stays for osteoarthritis ($24,000 vs. $16,000 per stay).
Figure 2 presents the distribution of nonmaternal, nonneonatal inpatient stays for each of the 20 most common principal diagnoses by primary expected payer. The distribution by payer for all nonmaternal, nonneonatal stays is also presented for comparison.

Figure 2. Top 20 principal diagnoses among nonmaternal, nonneonatal inpatient stays, by primary expected payer, 2018

Figure 2 is a bar chart that shows the distribution of nonmaternal, nonneonatal inpatient stays for the 20 most common principal diagnoses in 2018 by primary expected payer, as well as the distribution of all nonmaternal, nonneonatal stays.

Abbreviations: COPD, chronic obstructive pulmonary disease; ICD-10-CM, International Classification of Diseases, Tenth Revision, Clinical Modification
Notes: Diagnoses were identified using the Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Primary expected payer was missing for less than 0.3% of stays.
* Complication of select surgical or medical care, injury, initial encounter. This includes complications, such as infection, for surgical or medical care other than those from cardiovascular, genitourinary, or internal orthopedic devices or from organ/tissue transplants.
† Self-pay/No charge: includes self-pay, no charge, charity, and no expected payment.
Source: Agency for Healthcare Research and Quality (AHRQ), Healthcare Cost and Utilization Project (HCUP), National Inpatient Sample (NIS), 2018

Bar chart that shows the distribution of nonmaternal, nonneonatal inpatient stays for the 20 most common principal diagnoses in 2018 by primary expected payer, as well as the distribution of all nonmaternal, nonneonatal stays. Data are provided in Supplemental Table 1.

  • Medicare was the primary expected payer for nearly 60 percent of inpatient stays involving the 20 most frequent principal diagnoses.

    Medicare was the primary expected payer for the majority of nonmaternal, nonneonatal stays (52.1 percent of all stays and 57.7 percent of stays for the top 20 diagnoses combined) and the most common primary expected payer for 18 of the top 20 principal diagnoses (all conditions except for depressive disorders and schizophrenia spectrum disorders). The percentage of stays for the 18 common principal diagnoses for which Medicare was the most frequent payer ranged from 40.2 percent for biliary tract disease to 73.5 percent for heart failure.


  • Two mental disorder diagnoses—depressive disorders and schizophrenia spectrum disorders—were among the 20 most common diagnoses, and Medicaid was the primary expected payer for more than one-third of these stays.

    Among stays for schizophrenia spectrum and other psychotic disorders, Medicaid was the most common primary expected payer (41.9 percent of stays), followed by Medicare (36.3 percent) and private insurance (12.6 percent). Among stays for depressive disorders, Medicaid and private insurance each accounted for approximately one-third of stays (34.9 and 34.0 percent, respectively), with Medicare accounting for 18.0 percent.


  • Self-pay/no charge represented more than 7 percent of discharges for 4 of the top 20 diagnoses.

    For 4 of the top 20 principal diagnoses, self-pay/no charge accounted for more than 7 percent of stays: skin and subcutaneous tissue infections (7.9 percent), depressive disorders (7.7 percent), diabetes mellitus with complication (7.5 percent), and biliary tract disease (7.1 percent).
Most frequent principal diagnoses by patient and hospital characteristics, 2018
Table 2 presents statistics focusing on the five most frequent principal diagnoses among nonmaternal, nonneonatal stays in the United States by patient location (urbanicity) in 2018. Specifically, the rank of each principal diagnosis within each of the four patient locations is provided, along with the number of stays, rate per 100,000 population, mean length of stay, and mean cost per stay.

Table 2. Frequency and outcomes for the five most common principal diagnoses among nonmaternal, nonneonatal inpatient stays, by patient location, 2018
Rank within United States Principal diagnosis, patient location Rank within location category Number of stays Rate per 100,000 population Mean length of stay, days Mean cost per stay, $
1 Septicemia
Large central metropolitan 1 661,000 653.4 7.5 21,500
Large fringe metropolitan (suburbs) 1 502,300 618.3 7.1 18,500
Medium and small metropolitan 1 687,700 701.5 7.0 17,100
Micropolitan and noncore (rural) 1 354,300 768.4 6.6 16,600
2 Heart failure
Large central metropolitan 2 326,000 322.3 5.6 14,400
Large fringe metropolitan (suburbs) 3 267,500 329.3 5.5 13,100
Medium and small metropolitan 3 341,500 348.3 5.3 11,800
Micropolitan and noncore (rural) 3 195,000 422.9 4.9 11,300
3 Osteoarthritis
Large central metropolitan 3 262,200 259.2 2.1 16,300
Large fringe metropolitan (suburbs) 2 292,100 359.6 2.0 15,400
Medium and small metropolitan 2 363,900 371.2 2.0 15,300
Micropolitan and noncore (rural) 2 208,900 453.0 2.1 17,500
4 Pneumonia (except that caused by tuberculosis)
Large central metropolitan 5 178,100 176.1 4.9 11,600
Large fringe metropolitan (suburbs) 4 168,400 207.3 4.8 10,600
Medium and small metropolitan 4 225,300 229.8 4.8 9,800
Micropolitan and noncore (rural) 4 166,600 361.2 4.4 9,900
5 Diabetes mellitus with complication
Large central metropolitan 4 212,100 209.7 5.0 12,800
Large fringe metropolitan (suburbs) 7 148,500 182.9 4.8 11,700
Medium and small metropolitan 5 205,400 209.5 4.8 10,700
Micropolitan and noncore (rural) 8 107,600 233.4 4.6 10,600
Abbreviations: ICD-10-CM, International Classification of Diseases, Tenth Revision, Clinical Modification
Notes: Diagnoses were identified using the Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Number of stays is rounded to the nearest hundred. Mean cost per stay is rounded to the nearest $100.
Source: Agency for Healthcare Research and Quality (AHRQ), Healthcare Cost and Utilization Project (HCUP), National Inpatient Sample (NIS), 2018
Table 3 presents statistics for the five most frequent principal diagnoses among nonmaternal, nonneonatal stays by hospital region in 2018. Specifically, the rank of each principal diagnosis in the four regions is presented, along with the number of stays, rate per 100,000 population, mean length of stay, and mean cost per stay.

Table 3. Regional variation in frequency and outcomes for the five most common principal diagnoses among nonmaternal, nonneonatal inpatient stays, 2018
Rank within United States Principal diagnosis, hospital region Rank within regioin Number of stays Rate per 100,000 population Mean length of stay, days Mean cost per stay, $
1 Septicemia
Northeast 1 364,200 646.5 7.7 20,000
Midwest 1 457,8000 671.9 6.6 17,000
South 1 867,200 698.1 7.3 16,200
West 3 529,500 680.3 6.8 23,400
2 Heart failure
Northeast 3 211,100 374.8 5.9 14,100
Midwest 3 265,700 389.9 5.3 12,300
South 2 465,100 374.4 5.4 11,100
West 2 194,000 249.3 5.0 16,000
3 Osteoarthritis
Northeast 2 218,000 387.0 2.1 15,500
Midwest 2 292,600 429.4 2.0 15,700
South 3 391,600 315.2 2.2 14,900
West 2 225,900 290.2 1.9 18,600
4 Pneumonia (except that caused by tuberculosis)
Northeast 4 130,000 230.8 4.9 11,100
Midwest 4 180,900 265.5 4.5 10,100
South 4 310,800 250.2 4.8 9,400
West 6 119,100 153.0 4.5 13,200
5 Diabetes mellitus with complication
Northeast 6 117,600 208.7 5.4 13,000
Midwest 8 141,700 208.0 4.5 10,900
South 5 294,300 236.9 4.9 10,200
West 5 125,000 160.6 4.5 14,100
Abbreviations: ICD-10-CM, International Classification of Diseases, Tenth Revision, Clinical Modification
Notes: Diagnoses were identified using the Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Number of stays is rounded to the nearest hundred. Mean cost per stay is rounded to the nearest $100.
Source: Agency for Healthcare Research and Quality (AHRQ), Healthcare Cost and Utilization Project (HCUP), National Inpatient Sample (NIS), 2018

  • Septicemia was the most common principal diagnosis overall in the United States as well as within each region, with similar rates of stays across regions.

    The rate of septicemia stays was similar across regions, ranging from 646.5 per 100,000 population in the Northeast to 698.1 per 100,000 population in the South. However, the mean length of septicemia stays was higher in the Northeast (7.7 days) compared with the West and Midwest (6.8 and 6.6 days, respectively). The mean cost per septicemia stay was highest in the West ($23,400), followed by the Northeast ($20,000), with the cost in both regions higher than the cost in the Midwest and South ($17,000 and $16,200, respectively).


  • For three of the five top diagnoses, the rates of stays were lowest in the West compared with other regions.

    In 2018, the West had the lowest population rate of stays for heart failure, pneumonia, and diabetes mellitus with complication. For example, the rate of stays for heart failure was 249.3 per 100,000 population in the West compared with 374-390 per 100,000 in other regions. In contrast, the West had the highest mean cost per stay for heart failure ($16,000 in the West vs. $11,100-$14,100 in other regions), osteoarthritis ($18,600 vs. $14,900-$15,700), and pneumonia ($13,200 vs. $9,400-$11,100). For diabetes mellitus with complication, the West and Northeast had higher mean costs than the Midwest and South ($14,100 and $13,000 vs. $10,900 and $10,200 per stay, respectively).
Most frequent principal diagnoses among sex-age groups, 2018
Table 4 presents, for each sex-age group, the five most frequent principal diagnoses among nonmaternal, nonneonatal inpatient stays in 2018. The number of stays and the rate per 100,000 population are presented.

Table 4. Top five principal diagnoses among nonmaternal, nonneonatal inpatient stays by sex-age group, 2018
Rank Males Rank Females
Principal Diagnosis Number of stays Rate per 100,000 population Principal Diagnosis Number of stays Rate per 100,000 population
Ages 0-17 years 772,200 2,050.5 Ages 0-17 years 693,600 1,922.1
1 Acute bronchitis 58,300 154.7 1 Depressive disorders 63,800 176.7
2 Asthma 45,200 120.0 2 Acute bronchitis 40,800 113.1
3 Pneumonia 35,200 93.6 3 Pneumonia 30,600 84.8
4 Epilepsy; convulsions 34,000 90.2 4 Asthma 29,100 80.6
5 Depressive disorders 27,800 74.0 5 Epilepsy; convulsions 28,800 79.8
Ages 18-44 years 2,285,300 3,870.8 Ages 18-44 years 2,268,400 3,931.5
1 Schizophrenia spectrum, other psychotic disorders 148,300 251.2 1 Septicemia 161,100 279.3
2 Septicemia 142,500 241.3 2 Depressive disorders 128,400 222.5
3 Depressive disorders 115,200 195.0 3 Diabetes mellitus with complication 87,300 151.3
4 Diabetes mellitus with complication 98,300 166.4 4 Bipolar and related disorders 81,900 142.0
5 Alcohol-related disorders 90,500 153.2 5 Obesity 81,300 140.9
Ages 45-64 years 4.508,200 10,967.1 Ages 45-64 years 4,064,100 9,415.7
1 Septicemia 342,400 832.9 1 Septicemia 310,400 719.0
2 Osteoarthritis 189,100 460.1 2 Osteoarthritis 233,900 542.0
3 Heart failure 172,900 420.6 3 COPD and bronchiectasis 122,000 282.7
4 Acute myocardial infarction 172,700 420.2 4 Spondylopathies / spondyloarthropathy 112,200 259.9
5 Diabetes mellitus with complication 158,400 385.4 5 Heart failure 103,500 239.7
Ages 65-74 years 2,873,400 20,074.1 Ages 65-74 years 2,857,100 17,546.0
1 Septicemia 258,100 1,803.1 1 Osteoarthritis 259,800 1,595.3
2 Osteoarthritis 172,500 1,205.0 2 Septicemia 234,000 1,436.8
3 Heart failure 140,400 980.9 3 Heart failure 113,600 697.7
4 Acute myocardial infarction 111,000 775.6 4 COPD and bronchiectasis 94,300 579.1
5 Cardiac dysrhythmias 94,300 659.1 5 Cardiac dysrhythmias 76,900 472.3
Age 75+ years 3,233,700 37,421.6 Age 75+ years 4,273,700 34,090.0
1 Septicemia 348,500 4,033.3 1 Septicemia 397,500 3,171.1
2 Heart failure 248,700 2,877.7 2 Heart failure 307,000 2,448.5
3 Pneumonia 128,000 1,481.7 3 Urinary tract infections 173,000 1,379.8
4 Acute and unspecified renal failure 106,000 1,226.7 4 Osteoarthritis 159,200 1,270.0
5 Cardiac dysrhythmias 104,600 1,210.5 5 Pneumonia 159,000 1,268.3
Abbreviations: COPD, chronic obstructive pulmonary disease; ICD-10-CM, International Classification of Diseases, Tenth Revision, Clinical Modification
Notes: Diagnoses were identified using the Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. The pneumonia diagnosis group excludes pneumonia caused by tuberculosis. Number of stays is rounded to the nearest hundred.
Source: Agency for Healthcare Research and Quality (AHRQ), Healthcare Cost and Utilization Project (HCUP), National Inpatient Sample (NIS), 2018

  • Septicemia was the first or second most common diagnosis among both males and females for each adult age group.

    Septicemia was a very common principal diagnosis for adult males and females regardless of age. However, the population rate of septicemia increased with age and was more than 10 times higher among those aged 75+ years than those aged 18-44 years. The rate of septicemia was 16 percent higher for females than males aged 18-44 years, but the rate was higher for males than females in all older age groups: 16 percent higher for ages 45-64 years and 25 and 27 percent higher for ages 65-74 years and 75+ years, respectively. Septicemia was not among the most common diagnoses for children.


  • In 2018, mental and/or substance use disorders were among the top five principal diagnoses for the youngest age groups, 0-17 and 18-44 years.

    Although the order varied, the top five principal diagnoses were the same for both males and females aged 17 years and younger. These included three respiratory conditions (acute bronchitis, asthma, and pneumonia), epilepsy, and depressive disorders. Among this age group, the rate of stays for depressive disorders was more than twice as high for females as for males.

    Depressive disorders were also among the most common diagnoses for individuals aged 18-44 years. Several other mental and/or substance use disorders also ranked in the top five diagnoses for this age group: schizophrenia spectrum and other psychotic disorders and alcohol-related disorders for males and bipolar and related disorders for females.


  • For adults in the older age groups (45-64, 65-74, and 75+ years), cardiovascular and musculoskeletal diagnoses were among the top principal diagnoses by sex-age group.

    Heart failure ranked in the top five diagnoses for both males and females in each of the older age groups: 45-64, 65-74, and 75+ years. The population rate of heart failure increased with age and was always higher for males than for females, but the difference between the sexes narrowed with increasing age, from 75 percent higher for males versus females aged 45-64 years to 18 percent higher for males versus females aged 75+ years.

    Osteoarthritis was another common principal diagnosis among older adults, occurring in the top five diagnoses for both males and females in each of the three older age groups (with the exception of males aged 75+ years). The population rate of osteoarthritis was always higher for females than for males: 18 percent higher for females versus males aged 45-64 years, 32 percent higher for females versus males aged 65-74 years, and 17 percent higher for females versus males aged 75+ years (rate not shown in table for males aged 75+ years).
References

1 Centers for Medicare & Medicare Services. The Hospital Value-Based Purchasing (VBP) Program. Updated February 18, 2021. www.cms.gov/Medicare/Quality-Initiatives-Patient-Assessment-Instruments/Value-Based-Programs/HVBP/Hospital-Value-Based-Purchasing. Accessed March 5, 2021.

About Statistical Briefs

Healthcare Cost and Utilization Project (HCUP) Statistical Briefs provide basic descriptive statistics on a variety of topics using HCUP administrative healthcare data. Topics include hospital inpatient, ambulatory surgery, and emergency department use and costs, quality of care, access to care, medical conditions, procedures, and patient populations, among other topics. The reports are intended to generate hypotheses that can be further explored in other research; the reports are not designed to answer in-depth research questions using multivariate methods.

Data Source

The estimates in this Statistical Brief are based upon data from the HCUP 2018 National Inpatient Sample (NIS). Supplemental sources included population denominator data for use with HCUP databases, derived from information available from Claritas, a vendor that produces population estimates and projections based on data from the U.S. Census Bureau.a

Definitions

Diagnoses, ICD-10-CM, Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses, diagnosis-related groups (DRGs), and major diagnostic categories (MDCs)
The principal diagnosis is that condition established after study to be chiefly responsible for the patient's admission to the hospital. Secondary diagnoses are conditions that coexist at the time of admission that require or affect patient care treatment received or management, or that develop during the inpatient stay. All-listed diagnoses include the principal diagnosis plus the secondary conditions.

ICD-10-CM is the International Classification of Diseases, Tenth Revision, Clinical Modification. There are over 70,000 ICD-10-CM diagnosis codes.

The CCSR aggregates ICD-10-CM diagnosis codes into a manageable number of clinically meaningful categories.b The CCSR is intended to be used analytically to examine patterns of healthcare in terms of cost, utilization, and outcomes; rank utilization by diagnoses; and risk-adjust by clinical condition. The CCSR capitalizes on the specificity of the ICD-10-CM coding scheme and allows ICD-10-CM codes to be classified in more than one category. Approximately 10 percent of diagnosis codes are associated with more than one CCSR category because the diagnosis code documents either multiple conditions or a condition along with a common symptom or manifestation. For this Statistical Brief, the principal diagnosis code is assigned to a single default CCSR based on clinical coding guidelines, etiology and pathology of diseases, and standards set by other Federal agencies. The assignment of the default CCSR for the principal diagnosis is available starting with version v2020.2 of the software tool. ICD-10-CM coding definitions for each CCSR category presented in this Statistical Brief can be found in the CCSR reference file, available at www.hcup-us.ahrq.gov/toolssoftware/ccsr/ccs_refined.jsp#download. For this Statistical Brief, v2021.2 of the CCSR was used.

DRGs comprise a patient classification system that categorizes patients into groups that are clinically coherent and homogeneous with respect to resource use. DRGs group patients according to diagnosis, type of treatment (procedure), age, and other relevant criteria. Each hospital stay has one assigned DRG.

MDCs assign ICD-10-CM principal diagnosis codes to 1 of 25 general diagnosis categories. In this Statistical Brief, nonneonatal and nonmaternal hospitalizations are identified using the MDCs that are not equal to 14 (Pregnancy, Childbirth and the Puerperium) or 15 (Newborns and Other Neonates with Conditions Originating in the Perinatal Period).

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 1 year will be counted each time as a separate discharge from the hospital.

Population rates
Rates of stays per 100,000 population were calculated using 2018 hospital discharge totals in the numerator and Claritasc estimates of the corresponding 2018 U.S. population (e.g., the population for a specific sex-age group) in the denominator. Individuals hospitalized multiple times are counted more than once in the numerator.

Population rate of stays = number of stays among individuals in group divided by number of residents in group times 100,000.

Costs and charges
Total hospital charges were converted to costs using HCUP Cost-to-Charge Ratios based on hospital accounting reports from the Centers for Medicare & Medicaid Services (CMS).d Costs reflect the actual expenses incurred in the production of hospital services, such as wages, supplies, and utility costs; charges represent the amount a hospital billed for the case. For each hospital, a hospital-wide cost-to-charge ratio is used. Hospital charges reflect the amount the hospital billed for the entire hospital stay and do not include professional (physician) fees. For the purposes of this Statistical Brief, missing charges were imputed as the mean charge for the DRG before converting charges to costs. Costs are reported to the nearest hundred.

How HCUP estimates of costs differ from National Health Expenditure Accounts
There are a number of differences between the costs cited in this Statistical Brief and spending as measured in the National Health Expenditure Accounts (NHEA), which are produced annually by CMS.e The largest source of difference comes from the HCUP coverage of inpatient treatment only in contrast to the NHEA inclusion of outpatient costs associated with emergency departments and other hospital-based outpatient clinics and departments as well. The outpatient portion of hospitals' activities has been growing steadily and may exceed half of all hospital revenue in recent years. On the basis of the American Hospital Association Annual Survey, 2018 outpatient gross revenues (or charges) were about 49 percent of total hospital gross revenues.f

Smaller sources of differences come from the inclusion in the NHEA of hospitals that are excluded from HCUP. These include Federal hospitals (Department of Defense, Veterans Administration, Indian Health Services, and Department of Justice [prison] hospitals) as well as psychiatric, substance abuse, and long-term care hospitals. A third source of difference lies in the HCUP reliance on billed charges from hospitals to payers, adjusted to provide estimates of costs using hospital-wide cost-to-charge ratios, in contrast to the NHEA measurement of spending or revenue. HCUP costs estimate the amount of money required to produce hospital services, including expenses for wages, salaries, and benefits paid to staff as well as utilities, maintenance, and other similar expenses required to run a hospital. NHEA spending or revenue measures the amount of income received by the hospital for treatment and other services provided, including payments by insurers, patients, or government programs. The difference between revenues and costs includes profit for for-profit hospitals or surpluses for nonprofit hospitals.

Location of patients' residence
Place of residence is based on the urban-rural classification scheme for U.S. counties developed by the National Center for Health Statistics (NCHS) and based on the Office of Management and Budget (OMB) definition of a metropolitan service area as including a city and a population of at least 50,000 residents:
  • Large Central Metropolitan: Counties in a metropolitan area with 1 million or more residents that satisfy at least one of the following criteria: (1) containing the entire population of the largest principal city of the metropolitan statistical area (MSA), (2) having their entire population contained within the largest principal city of the MSA, or (3) containing at least 250,000 residents of any principal city in the MSA
  • Large Fringe Metropolitan: Counties in a metropolitan area with 1 million or more residents that do not qualify as large central metropolitan counties
  • Medium and Small Metropolitan: Counties in a metropolitan area of 50,000-999,999 residents
  • Micropolitan and Noncore: Counties in a nonmetropolitan area of 10,000-49,999 residents or a nonmetropolitan and nonmicropolitan area
Expected payer
To make coding uniform across all HCUP data sources, the primary expected payer for the hospital stay combines detailed categories into general groups:
  • Medicare: includes fee-for-service and managed care Medicare
  • Medicaid: includes fee-for-service and managed care Medicaid
  • Private insurance: includes commercial nongovernmental payers, regardless of the type of plan (e.g., private health maintenance organizations [HMOs], preferred provider organizations [PPOs])
  • Self-pay/No charge: includes self-pay, no charge, charity, and no expected payment
  • Other payers: includes other Federal and local government programs (e.g., TRICARE, CHAMPVA, Indian Health Service, Black Lung, Title V) and Workers' Compensation
Hospital stays that were expected to be billed to the State Children's Health Insurance Program (SCHIP) are included under Medicaid.

For this Statistical Brief, when more than one payer is listed for a hospital discharge, the first-listed payer is used.

Region
Region is one of the four regions defined by the U.S. Census Bureau:
  • Northeast: Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, and Pennsylvania
  • Midwest: Ohio, Indiana, Illinois, Michigan, Wisconsin, Minnesota, Iowa, Missouri, North Dakota, South Dakota, Nebraska, and Kansas
  • South: Delaware, Maryland, District of Columbia, Virginia, West Virginia, North Carolina, South Carolina, Georgia, Florida, Kentucky, Tennessee, Alabama, Mississippi, Arkansas, Louisiana, Oklahoma, and Texas
  • West: Montana, Idaho, Wyoming, Colorado, New Mexico, Arizona, Utah, Nevada, Washington, Oregon, California, Alaska, and Hawaii
About HCUP

The Healthcare Cost and Utilization Project (HCUP, pronounced "H-Cup") is a family of healthcare databases and related software tools and products developed through a Federal-State-Industry partnership and sponsored by the Agency for Healthcare Research and Quality (AHRQ). HCUP databases bring together the data collection efforts of State data organizations, hospital associations, and private data organizations (HCUP Partners) and the Federal government to create a national information resource of encounter-level healthcare data. HCUP includes the largest collection of longitudinal hospital care data in the United States, with all-payer, encounter-level information beginning in 1988. These databases enable research on a broad range of health policy issues, including cost and quality of health services, medical practice patterns, access to healthcare programs, and outcomes of treatments at the national, State, and local market levels.

HCUP would not be possible without the contributions of the following data collection Partners from across the United States:
Alaska Department of Health and Social Services
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
Delaware Division of Public Health
District of Columbia Hospital Association
Florida Agency for Health Care Administration
Georgia Hospital Association
Hawaii Laulima Data Alliance
Hawaii University of Hawai'i at Hilo
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
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 State Department of Health
Missouri Hospital Industry Data Institute
Montana Hospital Association
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 Office of Health Analytics
Pennsylvania Health Care Cost Containment Council
Rhode Island Department of Health
South Carolina Revenue and Fiscal Affairs Office
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 Department of Health and Human Resources, West Virginia Health Care Authority
Wisconsin Department of Health Services
Wyoming Hospital Association
About the NIS

The HCUP National (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 includes all payers. 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 the national and regional levels for specific subgroups of patients. In addition, NIS data are standardized across years to facilitate ease of use. Over time, the sampling frame for the NIS has changed; thus, the number of States contributing to the NIS varies from year to year. The NIS is intended for national estimates only; no State-level estimates can be produced. The unweighted sample size for the 2018 NIS is 7,105,498 (weighted, this represents 35,527,481 inpatient stays).

For More Information

For other information on hospital inpatient stays, refer to the HCUP Statistical Briefs located a www.hcup-us.ahrq.gov/reports/statbriefs/sb_hospoverview.jsp.

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

For a detailed description of HCUP and more information on the design of the National Inpatient Sample (NIS), please refer to the following database documentation:

Agency for Healthcare Research and Quality. Overview of the National (Nationwide) Inpatient Sample (NIS). Healthcare Cost and Utilization Project (HCUP). Rockville, MD: Agency for Healthcare Research and Quality. Updated December 2020 www.hcup-us.ahrq.gov/nisoverview.jsp. Accessed January 22, 2021.

Suggested Citation

McDermott KW (IBM Watson Health), Roemer M (AHRQ). Most Frequent Principal Diagnoses for Inpatient Stays in U.S. Hospitals, 2018. HCUP Statistical Brief #277. July, 2021. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/reports/statbriefs/sb277-Top-Reasons-Hospital-Stays-2018.pdf.

Acknowledgments

The authors would like to acknowledge the contributions of Nils Nordstrand of IBM Watson Health.

***

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 email us at hcup@ahrq.gov or send a letter to the address below:

Joel W. Cohen, Ph.D., Director
Center for Financing, Access and Cost Trends
Agency for Healthcare Research and Quality
5600 Fishers Lane
Rockville, MD 20857


This Statistical Brief was posted online on July 13, 2021.


a Claritas. Claritas Demographic Profile by ZIP Code. https://claritas360.claritas.com/mybestsegments/.Exit Disclaimer Accessed January 22, 2021.
b Agency for Healthcare Research and Quality. HCUP Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP). Agency for Healthcare Research and Quality. Updated November 2020. https://hcup-us.ahrq.gov/toolssoftware/ccsr/dxccsr.jsp. Accessed June 22, 2021.
c Claritas. Claritas Demographic Profile by ZIP Code. https://claritas360.claritas.com/mybestsegments/.Exit Disclaimer Accessed January 22, 2021.
d Agency for Healthcare Research and Quality. HCUP Cost-to-Charge Ratio (CCR) Files. Healthcare Cost and Utilization Project (HCUP). 2001-2017. Agency for Healthcare Research and Quality. Updated September 2020. www.hcup-us.ahrq.gov/db/state/costtocharge.jsp. Accessed January 22, 2021.
e For additional information about the NHEA, see Centers for Medicare & Medicaid Services (CMS). National Health Expenditure Data. CMS website. Updated December 17, 2019. www.cms.gov/Research-Statistics-Data-and-Systems/Statistics-Trends-and-Reports/NationalHealthExpendData/index.html?redirect=/NationalHealthExpendData/. Accessed January 22, 2021.
f American Hospital Association. TrendWatch Chartbook, 2020. Table 4.2. Distribution of Inpatient vs. Outpatient Revenues, 1995-2018. www.aha.org/system/files/media/file/2020/10/TrendwatchChartbook-2020-Appendix.pdf. Exit Disclaimer Accessed January 22, 2021.



Supplemental Table 1. Top 20 principal diagnoses among nonmaternal, nonneonatal inpatient stays, by primary expected payer, 2018, for data presented in Figure 2
Principal diagnosis % of all stays
Medicare Medicaid Private insurance Self-pay/No charge† Other
All nonmaternal, nonneonatal stays 52.1 16.7 23.6 4.6 2.8
Top 20 principal diagnoses 57.7 14.9 20.9 3.8 2.6
Septicemia 61.3 14.8 17.8 4.0 2.0
Heart failure 73.5 10.5 11.2 3.0 1.8
Osteoarthritis 57.5 4.4 34.5 0.5 3.0
Pneumonia (except that caused by tuberculosis) 63.1 14.5 17.3 3.0 1.9
Diabetes mellitus with complication 43.2 24.9 21.8 7.5 2.4
Acute myocardial infarction 57.5 9.6 25.2 4.8 2.8
Cardiac dysrhythmias 68.2 6.7 20.6 2.4 2.0
COPD and bronchiectasis 69.2 14.4 11.6 2.7 2.0
Acute and unspecified renal failure 68.6 11.0 15.0 3.4 1.9
Cerebral infarction 65.4 9.2 19.0 4.1 2.1
Skin and subcutaneous tissue infections 41.9 24.2 22.9 7.9 2.9
Depressive disorders 18.0 34.9 34.0 7.7 5.2
Spondylopathies/spondyloarthropathy 49.2 8.4 34.3 1.4 6.5
Urinary tract infections 67.8 12.8 14.6 3.2 1.5
Respiratory failure; insufficiency; arrest 61.0 18.1 15.4 3.0 2.5
Schizophrenia spectrum, other psychotic disorders 36.3 41.9 12.6 5.6 3.3
Coronary atherosclerosis, other heart disease 58.8 9.5 25.5 3.1 3.0
Biliary tract disease 40.2 18.4 31.6 7.1 2.6
Fluid and electrolyte disorders 61.2 17.8 15.9 3.1 1.9
Complication of care, injury* 46.9 18.1 29.1 2.7 3.1
* Complication of select surgical or medical care, injury, initial encounter. This includes complications, such as infection, for surgical or medical care other than those from cardiovascular, genitourinary, or internal orthopedic devices or from organ/tissue transplants.
† Self-pay/No charge: includes self-pay, no charge, charity, and no expected payment.



Internet Citation: Statistical Brief #277. Healthcare Cost and Utilization Project (HCUP). July 2021. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/reports/statbriefs/sb277-Top-Reasons-Hospital-Stays-2018.jsp.
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