a b s t r a c t

Background: Spending on emergency department (ED) services in recent years has increased faster than spend- ing in any other area of healthcare. Analyzing growth rates of ED treatment costs by patient and hospital attri- butes may illuminate ways to reduce overall hospital cost growth. Prior studies have examined changes in ED visit charges and expenditures over time, but little research has focused on changes in ED treatment costs.

Methods: We analyzed trends in ED treatment costs by applying the Healthcare Cost and Utilization Project (HCUP) Cost-to-Charge Ratios for ED Files to the 2012-2019 HCUP Nationwide Emergency Department Sample. Specifically, we estimated treatment cost per ED visit, mean and Total costs by patient and hospital characteristics, and compound annual growth rate in costs and patient volumes.

Results: During 2012-2019, ED treatment costs increased from $54 billion to $88 billion, a 5.4% annual growth rate-with 4.4 percentage points attributable to higher treatment cost per visit. Growth rates varied by patient and hospital attribute.

Conclusions: By highlighting overall ED cost trends, as well as specific segments of the delivery system with the most rapidly increasing costs, this study provides important information for policymakers and hospital decisionmakers.

Published by Elsevier Inc.

1. Introduction

U.S. healthcare spending on emergency department (ED) visits is substantial and growing rapidly. In 2019, 13.6% of the population in- curred at least one expense for an ED visit, with an average expenditure of $1082 per visit [1]. Between 2006 and 2016, ED spending grew at an annualized rate of 4.4%, outpacing the growth in total healthcare spend- ing (1.4%) [2].

Although ED services constitute a small component of hospital costs, the frequency of avoidable visits-estimated to account for 3.3% to 6.3% of ED encounters [3,4]-indicates an opportunity for savings because similar nonurgent services are less costly in outpatient settings [5,6]. Analyzing growth rates of ED treatment costs by patient and hospital at- tributes may illuminate ways to reduce overall hospital cost growth.

* Corresponding author.

E-mail addresses: [email protected] (G. Pickens), [email protected] (K.W. McDermott), [email protected] (A. Mummert), [email protected] (Z. Karaca).

Prior studies have examined changes in ED visit charges [7] and ex- penditures [1,8] over time, but little research has focused on changes in ED treatment costs. In part, this may have reflected insufficient methods for estimating ED-specific treatment costs from charge data. We applied the recently developed Healthcare Cost and Utilization Project (HCUP) ED Cost-to-Charge Ratios (CCRs) for the Nationwide Emergency Depart- ment Sample (NEDS), which enable the conversion of hospital charges to hospital costs. The methods used to develop these ED CCRs result in considerably more specificity in estimated ED treatment costs than ear- lier hospital-level cost analyses [9]. We illustrated the application of these CCRs through an analysis of U.S. ED treatment costs.

1. Methods
   1. Study design and data sources

We conducted a retrospective observational study of ED treatment cost trends in U.S. hospital-based EDs from 2012 to 2019. Some ED visits resulted in hospital admission, whereas others (treat-and-release visits) did not.

https://doi.org/10.1016/j.ajem.2022.05.035 0735-6757/Published by Elsevier Inc.

We obtained yearly ED data from the Agency for Healthcare Re- search and Quality (AHRQ) HCUP NEDS for 2012-2019 [10]. The NEDS is the largest all-payer ED database in the United States, comprising a stratified sample of about 20% of all hospital-based EDs. It contains data from approximately 33 million ED visits in 2019, or a weighted total of about 143 million visits. The NEDS includes adult and pediatric hospitals with and without trauma centers. For comparison, we also ob- tained 2012-2019 inpatient data from the AHRQ HCUP National Inpa- tient Sample (NIS) [11]. The HCUP databases are consistent with the definition of limited data sets under the Health Insurance Portability and Accountability Act Privacy Rule and contain no direct patient iden- tifiers. The AHRQ Human Protections Administrator has determined this project does not constitute research involving human subjects; thus, it was not required by the Agency to be submitted to an Institutional Review Board.

Several NEDS features make it ideal for investigating ED treatment cost trends. Its large sample size provides sufficient data for analysis of uncommon disorders and procedures across hospital types. The NEDS includes clinical information about each ED visit (e.g., all-listed diagno- ses), hospital characteristics (e.g., teaching status), and patient charac- teristics (e.g., demographic information). In data years 2012 and 2019, ED charge information is available for 85% and 95% of visits, respectively, including those with an expected payer of Medicare, Medicaid, private insurance, self-pay, and “no charge.”

Patient-level variables derived from the NEDS include patient age group, sex, expected primary payer, and urban/rural residence location. To determine the main reason for the ED visit, we used the primary di- agnosis, grouped by International Classification of Diseases, Ninth Revi- sion, Clinical Modification (ICD-9-CM) or Tenth Revision (ICD-10-CM) chapter. Hospital characteristics included hospital region, ownership, bed size, teaching status, urban/rural location, and trauma level.

• 1. Analytic approach

We estimated costs for all ED visits by patient and hospital charac- teristics for each year studied. First, we estimated visit-specific ED

costs by multiplying Total charges for ED services by the HCUP ED CCR for the hospital. We then computed mean costs by averaging the visit- specific cost estimate, weighted by the NEDS discharge weight, for each analysis group and year. Finally, we estimated total costs as the product of mean cost and number of ED visits for each analysis group and year. This average-costing approach was necessary because some visit records in the NEDS, as noted above, did not have total charges.

Total costs are driven by visit volumes and cost per visit, so we report both quantities. We translated changes in costs and visit volumes into estimates of compound annual growth rate (hereinafter “growth rate”) for 2012-2019 [12]. We used the Gross domestic product (GDP) deflator to adjust the cost and charge estimates for inflation [13]. Because of the large number of records in the NEDS, we reported point estimates of mean charges, costs, and Percentage change. Due to the large sample size (>30 million), virtually any comparison made in

our study would be statistically significant.

1. Results

Table 1 presents visit rates, charges, and costs for 2012-2019 for all ED visits, treat-and-release visits, and visits that resulted in hospital ad- mission, with comparison metrics for inpatient stays, the U.S. popula- tion, and GDP deflator. Overall, total ED visit costs increased from $54 billion in 2012 to $88 billion in 2019. This increase implied an inflation-adjusted growth rate of 5.4%, of which 4.4 percentage points were attributable to growth in mean cost per visit and the remainder to growth in visits. The 8.3% growth rate for ED visit charges far exceeded the growth rate of 1.7% for the GDP deflator over the same period.

Table 2 presents 2012-2019 growth rates for ED visit total costs, vol- ume, and mean cost per visit by hospital characteristic and the corre- sponding growth rates for the number of hospitals in each category. Hospitals in the Midwest had the largest increase in mean cost per ED visit (4.7% growth rate). The greatest increase in total visits occurred in the South and West (1.3% to 1.4%). The smallest increase in total costs (3.5%) and mean cost per visit (3.2%) occurred in the Northeast.

Table 1

Total emergency department visits, charges, and costs 2012-2019^a

Costs and charges	2012	2019	Growth rateb 2012-2019 (%) real $c	Growth rateb 2012-2019 (%) nominal $
U.S. ED costs ($ millions)	54474	88223	5.4	7.1
ED charge mean ($): all visits	2430	4773	8.3	10.1
ED charge mean ($): T&R visits	2506	4969	8.5	10.3
ED charge mean ($): admitted visits	1911	3185	5.8	7.6
ED cost mean ($): all visits	405	615	4.4	6.1
ED cost mean ($): T&R visits	420	642	4.5	6.2
ED cost mean ($): admitted visits	305	397	2.1	3.8
U.S. IP costs ($ millions)	377455	472464	1.6	3.3
Visits, rate, population, and price deflator		2012	2019	Growth rate 2012-2019 (%)
U.S. ED visits (N millions): all visits		134.4	143.4	0.9
ED visits (N millions): T&R visits		115.3	123.1	0.9
ED visits (N millions): admitted visits		19.1	20.4	0.9
ED visit rate (per 100,000 population): all		42825	43697	0.3
ED visit rate (per 100,000 population): T&R		36749	37491	0.3
ED visit rate (per 100,000 population): admitted		6077	6207	0.3
U.S. IP discharges (N millions)		36.5	35.2	-0.5
IP discharge rate (per 100,000 population)		11626	10729	-1.1
U.S. population (N millions)		313.8	328.2	0.6
Implicit price deflators for GDP		100.00	112.29	1.7

Abbreviations: ED, emergency department; GDP, gross domestic product; IP, inpatient; T&R, treat and release.

^a Sources for this table are the Agency for Healthcare Research and Quality (AHRQ), Healthcare Cost and Utilization Project (HCUP), Nationwide Emergency Department Sample, 2012-2019; Centers for Medicare & Medicaid Services, Healthcare Cost Report Information System Public Use Files, 2012-2019; AHRQ, HCUP, National Inpatient Sample, 2012-2019; U.S. Census Bureau, National Population Totals and Components of Change: 2010-2019 (https://www.census.gov/data/datasets/time-series/demo/popest/2010s-national-total.html); and Bureau of Economic Analysis, GDP Implicit Price Deflator (https://apps.bea.gov/iTable/iTableHtml.cfm?reqid=19&step=3&isuri=1&1921=survey&1903=13).

^b Compound annual growth rate.

^c Adjusted for inflation.

Change in emergency department visits and costs and number of hospitals by hospital characteristics, 2012-2019^a

Hospital characteristic	2012				Growth rateb 2012-2019 (%)
	Total costs ($ millions)	Total no. of visits (millions)	Mean cost per visit ($)		Total costs Total no. of Mean cost per visit No. of (real $)c visits (real $)c hospitals
All hospitals	54474	134	405		5.4 0.9 4.4 -0.3
Census region
Northeast	11143	25	437	3.5		0.2	3.2	-0.3
Midwest	13686	31	438	5.1		0.4	4.7	-0.2
South	18932	53	356	5.1		1.3	3.8	-0.6
West	13053	24	535	5.2		1.4	3.7	0.3
Urban-rural definition
Large metropolitan areas with >=1 million residents	28238	66	428	5.5		1.5	3.9	0.5
Small metropolitan areas with <1 million residents	17152	45	385	5.7		1.1	4.6	0.5
Micropolitan areas	5810	16	368	4.6		-0.7	5.4	-1.5
Not metropolitan or micropolitan (rural)	3407	8	422	3.1		-1.9	5.1	-1.3
Control/ownership
Government, nonfederal	8127	19	424	5.2		0.1	5.1	-1.3
Private, not-for-profit	40551	96	424	5.5		1.0	4.4	0.2
Private, investor-owned	5900	20	301	4.5		1.4	3.1	-0.5
Trauma level designation
Not a trauma center	33140	85	391	2.6		-1.5	4.2	-1.4
Level I	9116	20	459	8.6		3.5	4.9	2.4
Level II	8323	19	431	6.5		2.5	4.0	1.3
Level III	3891	10	374	14.0		9.1	4.4	7.5

^a The source for this table is the Agency for Healthcare Research and Quality, Healthcare Cost and Utilization Project, Nationwide Emergency Department Sample, 2012-2019.

^b Compound annual growth rate.

^c Adjusted for inflation.

Micropolitan and Rural hospitals had larger increases in mean cost per visit relative to more urban areas (5.1% to 5.4% growth rate vs. 3.9% to 4.6%) but smaller increases in total ED costs (3.1% to 4.6% vs. 5.5% to 5.7%). The smaller total cost increases are likely explained in part by the decrease in micropolitan and rural hospitals (-1.5% to

-1.3% growth rates) and visits to these hospitals (-1.9% to -0.7%) over time.

Private for-profit hospitals experienced smaller ED cost increases compared with public and private not-for-profit hospitals (4.5% vs. 5.2% to 5.5% growth rate for total ED costs; 3.1% vs. 4.4% to 5.1% for mean cost per ED visit) but a larger increase in total number of visits (1.4% vs. 0.1% to 1.0%). Level III trauma centers had the highest growth rate for total costs (14.0%) and total visits (9.1%), driven mainly by a substantial increase in their number (7.5% growth rate).

Table 3 presents growth rates for ED visit costs and volume by patient characteristic. Total ED cost growth generally increased with age, ranging from a 2.7% growth rate for patients aged 0-9 years to 8.9% for patients aged >=65 years. A rising number of ED visits (4.0% growth rate) and in- creasing mean cost per visit (4.7%) drove rising costs for the oldest group. Total ED cost increases were greatest for patients in fringe counties of metropolitan areas with populations of >=1 million and for patients in counties in metropolitan areas with populations of 250000-999999 (6.3% to 6.5%). The growth rate for mean cost per ED visit was lowest among patients living in central counties of metropolitan areas with pop- ulations of >=1 million (3.0%). Growth rates for total ED costs and total ED visits were highest among patients with Medicare or Medicaid as their primary expected payer (6.6% to 7.8% for costs and 2.0% to 2.9% for visits) but negative for those with an expected payer of self-pay or no charge (-2.6% to -0.3% for costs; -3.4% to -1.6% for visits).

Total ED cost increases were greatest for Infectious conditions and neo- plasms (9.0% to 9.1%); the lowest increases were for injury and poisoning and symptoms not elsewhere classified (3.7% to 3.9%). Conditions of the nervous system also had a substantial increase in total ED costs (8.0%), driven by a higher than average increase in mean cost per visit (8.0%).

Patients transferred to home health care or to a skilled nursing facil- ity, Intermediate care facility, or another facility type were associated with the highest growth rates for total ED costs (17.3% and 10.2%, re- spectively). In particular, ED visits requiring transfer to home health care increased over the reporting period by 12.3%, representing a key cost driver.

1. Discussion
   1. Summary of results

ED costs increased from $54 billion to $88 billion from 2012 to 2019, reflecting a growth rate of 5.4%. This increase is consistent with an earlier estimate of a 6.4% annualized growth rate in ED spending from 1996 to 2013 [14]. Galarraga and Pines [15] estimated $110 billion in expendi- tures for outpatient ED encounters in 2010, approximately twice our 2012 estimate of $54 billion in total ED facility costs. Expenditures (pay- ments) are generally higher than delivery costs and include physician ser- vices, drugs, supplies, and other fees associated with ED episodes of care. Yun et al. [8] estimated per visit ED expenditures by Insurance type from 1996 to 2015. The closest comparator to our cost estimates is for ED visits covered by Medicare. For 2012-2013, the authors reported me- dian expenditures per ED visit of $532 for Medicare, similar to our 2012 per visit estimate of $500 when Medicare was the primary expected payer. Our findings also highlight hospital and patient attributes associated with above- or below-average ED cost increases. Some variances are at- tributable to factors other than ED treatment cost inflation. For example, the large cost increase associated with Trauma III hospitals is attribut- able to federal, state, and local initiatives to increase the number of

these hospitals over time [16].

We also found a large increase in ED visit costs for patients aged >=65 years and those with Medicare coverage. Part of this growth is due to the aging Baby Boomer population. While the total U.S. population grew by 5% between 2012 and 2019, the population aged >=65 years grew by 25% [17]. We also observed a large increase for Medicaid- covered patients and a decrease for patients expected to self-pay. The rise in insurance coverage that followed implementation of the Afford- able Care Act may promote the use of primary care and urgent care cen- ters, but the increase in Medicaid enrollment appears to have increased ED visits by Medicaid enrollees nationally.

• 1. Limitations

We acknowledge several limitations. Sophisticated cost-accounting methods can yield costs for specific hospital services and may be more ac- curate than the methodology used in this study, but these are not widely available in nationwide databases. Our analysis is limited to facility costs,

Table 3

Change in emergency department visits and costs by selected patient characteristics, 2012-2019^a

Patient characteristic	2012				Growth rateb	2012-2019 (%)
	Total costs ($ millions)	Total no. of visits (millions)	Mean cost per visit ($)		Total costs (real $)c	Total no. of visits	Mean cost per visit (real $)c
Total	54474	134	405		5.4	0.9	4.4
Age group (years)
0-9	3770	18.5	204		2.7	-1.2	3.9
10-14	1460	5.3	277		3.8	-0.1	3.9
15-17	1407	4.1	339		2.8	-0.8	3.6
18-44	20504	52.9	388		3.7	-0.1	3.7
45-64	15110	30.5	495		5.6	1.7	3.9
65+	12300	23.1	533		8.9	4.0	4.7
Sex
Male	23875	59.9	399	5.6		1.1	4.5
Female	30589	74.5	411	5.2		0.8	4.3
patient location: NCHS urban-rural code
Central counties of metro areas of >=1 million	16652	37.1	448	4.3		1.3	3.0
Fringe counties of metro areas of >=1 million	11884	29.2	407	6.3		1.3	4.9
Counties in metro areas of 250,000-999,999	11103	29.6	374	6.5		1.6	4.9
Counties in metro areas of 50,000-249,999	4743	12.5	381	4.9		0.0	4.8
Micropolitan counties	5904	15.7	376	4.4		-0.9	5.4
Not metropolitan or micropolitan counties	4159	9.6	431	4.6		0.2	4.4
Primary expected payer
Medicare	14580	29.1	500	7.8		2.9	4.8
Medicaid	12052	37.9	318	6.6		2.0	4.5
Private insurance	16646	37.1	448	5.3		1.2	4.0
Self-pay	8270	22.4	369	-0.3		-3.4	3.2
No charge	337	0.8	442	-2.6		-1.6	-1.0
Other	2536	6.9	370	2.0		-3.1	5.2
Condition (ICD chapter)
Other/unknown	1339	4.9	271	4.4		-0.2	4.6
Infectious	1196	4.4	272	9.1		3.1	5.8
Neoplasms	290	0.6	489	9.0		3.1	5.6
Endocrine	1148	2.4	471	8.5		3.4	5.0
Blood disorders	390	0.8	498	8.1		2.4	5.5
Mental and Substance use disorders	2076	5.2	399	5.0		1.8	3.1
Nervous system	1959	7.4	263	8.0		0.0	8.0
Circulatory	3436	6.2	553	8.0		2.8	5.0
Respiratory	4224	14.6	289	5.8		1.2	4.5
Digestive	4391	9.4	469	7.7		1.3	6.3
Genitourinary	3770	7.6	496	5.2		0.9	4.3
Pregnancy/childbirth	1314	3.3	401	5.2		3.5	1.7
Skin	1153	5.4	215	4.2		-1.3	5.6
Musculoskeletal	2710	8.5	318	6.7		2.5	4.0
Congenital	27	0.1	534	5.7		1.1	4.6
Perinatal	40	0.2	257	5.3		1.6	3.6
Symptoms not elsewhere classified	15564	26.4	589	3.7		1.3	2.4
Injury and poisoning	9478	27.0	351	3.9		-1.2	5.1
Disposition from the ED
Routine	43969	109.0	403	5.2		0.8	4.3
Transfer to short-term hospital	1949	2.2	904	7.1		2.3	4.6
Transfer to skilled nursing facility, intermediate care facility, or another type of facility	1149	1.5	748	10.2		4.4	5.5
Home health care	255	0.2	1595	17.3		12.3	4.4
Against medical advice	721	2.1	346	6.1		1.4	4.7
Admitted as an inpatient to the same hospital	5817	19.1	305	3.1		0.9	2.1
Died in the ED	154	0.2	821	6.9		1.0	5.9

Abbreviations: ED, emergency department; ICD, International Classification of Diseases; NCHS, National Center for Health Statistics.

^a The source for this table is the Agency for Healthcare Research and Quality, Healthcare Cost and Utilization Project, Nationwide Emergency Department Sample, 2012-2019.

^b Compound annual growth rate.

^c Adjusted for inflation.

which exclude most professional services and thus may misrepresent trends in total ED spending. Our study may underestimate ED costs for pa- tients who were subsequently admitted, because ED charges in the NEDS exclude ancillary services (e.g., computed tomography scans) used in the ED before inpatient admission. In fact, Table 1 confirms that mean costs and charges were lower for admitted ED visits than for treat-and- release visits. Finally, the October 2015 transition to ICD-10-CM may have affected the quality of diagnosis coding, at least for a time. Our

analysis period includes care received before and after this date. However, mapping Diagnosis codes into broad categories (chapters) before and after the coding transition should minimize its impact (see Appendix).

• 1. Implications

Our study used the recently developed HCUP ED CCRs to estimate trends in delivery costs for ED services by various patient and hospital

characteristics. From 2012 to 2019, total costs of ED visits rose rapidly, increasing at an inflation-adjusted annual rate of 5.4%, and mean cost per visit rose by 4.4% annually-both rates much higher than general inflation. By highlighting overall ED cost trends, as well as specific seg- ments of the delivery system with the most rapidly increasing costs, this study provides important information for policymakers and hospi- tal decisionmakers.

Authors’ statement

The views expressed in this article are those of the authors and do not necessarily reflect those of the Agency for Healthcare Research and Quality or the U.S. Department of Health and Human Services. We used Nationwide Emergency Department Sample data from the Healthcare Cost and Utilization Project for this study. For information about how to obtain a copy of these data, visit https://www.hcup-us. ahrq.gov.

CRediT authorship contribution statement

Gary Pickens: Writing - review & editing, Writing - original draft, Methodology, Formal analysis, Data curation, Conceptualization. Mark

W. Smith: Writing - review & editing, Writing - original draft, Valida- tion, Methodology. Kimberly W. McDermott: Writing - review & editing, Writing - original draft, Validation, Project administration, Data curation, Conceptualization. Amanda Mummert: Writing - review & editing, Project administration, Data curation, Conceptualization. Zeynal Karaca: Writing - review & editing, Validation, Supervision, Pro- ject administration, Methodology, Data curation, Conceptualization.

Funding

The author(s) disclose receipt of the following financial support for the research, authorship, and/or publication of this article: This study received funding from Agency for Healthcare Research and Quality contract HHSA-290-2018-00001-C.

Appendix A. Mapping of ICD-9-CM and ICD-10-CM codes to chapters

Disease category	ICD-9-CM codes	ICD-10-CM codes
Blood disorders	280-289	D50-D89
Congenital	740-759	Q00-Q99
Musculoskeletal	710-739	M00-M99
Perinatal	760-779	P00-P96
Respiratory	460-519	J00-J99
Skin	680-709	L00-L99
Circulatory	390-459	I00-I99
Digestive	520-579	K00-K95
Endocrine	240-279	E00-E89
Genitourinary	580-629	N00-N99
Infectious	001-139	A00-B99
Injury	800-909.2, 909.4, 909.9, 910-994.9, 995.5-995.59, and 995.80-995.85	All S codes, T07-T34, T51-T76, T79, and T36-T50 with a 6th character of 1, 2, 3, or 4, except: T36.9, T37.9, T39.9, T41.4, T42.7,
Mental and	290-319	T43.9, T45.9, T47.9, and T49.9 with a 5th character of 1, 2, 3, or 4 F01-F99

substance use disorders

Neoplasms 140-239 C00-D49

Declaration of Competing Interest

Nervous system and 320-389 G00-G99 and H00-H95

sense organs

Pregnancy/childbirth 630-679 O00-O9A

Respiratory 460-519 J00-J99

The author(s) declare(s) that there is no conflict of interest.

Acknowledgments

Symptoms not elsewhere classified

780-799 R00-R99

The authors gratefully acknowledge Mary Beth Schaefer and Paige Jackson of IBM Watson Health for providing editorial review of the manuscript. We also wish to acknowledge the 38 Healthcare Cost and Utilization Project (HCUP) State Partner organizations that contributed to the HCUP Nationwide Emergency Department Sample (NEDS) data- bases used in this study: Arizona Department of Health Services, Arkan- sas Department of Health, California Office of Statewide Health Planning and Development, Colorado Hospital Association, Connecticut Hospital Association, 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 De- partment of Public Health, Indiana Hospital Association, Iowa Hospital Association, Kansas Hospital Association, Kentucky Cabinet for Health and Family Services, Maine Health Data Organization, Maryland Health Services Cost Review Commission, Massachusetts Center for Health In- formation and Analysis, Minnesota Hospital Association (provides data for Minnesota and North Dakota hospitals), Mississippi State Depart- ment of Health, Missouri Hospital Industry Data Institute, Montana Hos- pital Association, Nebraska Hospital Association, Nevada Department of Health and Human Services, New Jersey 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, Oregon Association of Hospitals and Health Systems, Oregon Office of Health Analytics, 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, Wisconsin Department of Health Services, and Wyoming Hospital Association.

Abbreviations: ICD-9-CM, International Classification of Diseases, Ninth Revision, Clinical Modification; ICD-10-CM, Internal Classification of Diseases, Tenth Revision, Clinical Modification.

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