Assessment of Annual Cost of Substance Use Disorder in US Hospitals

Key Points Question How much does substance use disorder cost each year in US hospitals? Findings In this economic evaluation of 124 573 175 hospital emergency department encounters and 33 648 910 hospital inpatient encounters, the annual medical cost associated with substance use disorder in US emergency departments and inpatient settings exceeded $13 billion in 2017. Meaning These findings suggest that costs associated with substance use disorder are high; costs of treatment and prevention could potentially be offset by reducing the direct medical cost of substance use disorder.


Introduction
The US drug overdose death rate has more than tripled in 2 decades, reaching more than 70 000 deaths in 2019. 1 In the most recent available data, hospital admissions with principal diagnosis of mental health or substance use disorder (SUD) increased 12% from 2005 to 2014 and emergency department (ED) visits increased 44% from 2006 to 2014. 2,3 Hospital encounters with SUD as a concomitant condition (not principal diagnosis) are also increasing; admissions documenting patients' opioid use disorder without overdose quadrupled from 1993 to 2016 (to 155 discharges per 100 000 population). 4 These trends create urgency to estimate attributable direct costs to assist in identifying costeffective ways to prevent SUD and link people to effective treatment. Previous analysis has addressed the prevalence and mean cost of hospital encounters that include mental health or SUD diagnosis. 5 Decision-making about SUD prevention investment can benefit more from the estimated total cost of hospital care that is attributable to SUD-that is, the cost that potentially could be minimized through successful prevention or treatment. The attributable cost of SUD in US hospitals can be derived through person-based statistical models of medical costs, which compare patients with and without a health condition. 6 This study aimed to use nationally representative data to estimate the attributable direct annual medical cost of SUD in US hospitals.

Methods
This economic evaluation did not require institutional board review or informed patient consent because all data were publicly available and no human participants were involved, per 45 CFR part 46. This study followed the relevant sections of the Consolidated Health Economic Evaluation Reporting Standards (CHEERS) reporting guideline. 7 We analyzed the 2017 Healthcare Cost and Utilization Project Nationwide Emergency Department Sample (HCUP-NEDS) and National Inpatient Sample (HCUP-NIS), which offer surveyweighted national estimates of community hospital encounters based on discharge records.

Diagnoses by International Statistical Classification of Diseases, Tenth Revision, Clinical Modification
(ICD-10-CM) code, including SUD (Table 1), were classified by Clinical Classification Software Refined groups. ED records indicating admission to the same hospital and inpatient records indicating transfer admission from another hospital were excluded to avoid double counting. Elixhauser Comorbidity Software identified patient comorbidities. 8 The main outcome measures were the total The provenance of this study's cost data supports monetary results presented in terms of medical costs, rather than payments or reimbursements (which are relevant terms when financial transactions from medical claims constitute the primary basis for estimated medical costs).

Statistical Analysis
These results reflect appropriate reweighting after excluding records (10% of eligible) with missing data (charges, diagnosis code, sex, age, primary payer, disposition, or length of inpatient stay). The associated medical cost of SUD overall and by substance type was calculated using discretely estimated adjusted mean associated costs of principal and secondary SUD diagnoses from 2 multivariable generalized linear models of total encounter cost, controlling for patient demographic, clinical, and insurance characteristics. Statistical analysis was conducted with SAS version 9.4 (SAS Institute) and Stata version 16 (StataCorp) from March to June 2020.
Model 1 included only encounters with principal SUD diagnosis (eg, drug overdose) and controlled for all secondary SUD diagnoses. The mean of that model's estimated values (using Stata's margins command) was the estimated adjusted mean cost of an encounter with a principal SUD diagnosis ( Table 2).  c These are survey-weighted estimates. Encounters could have both principal and secondary SUD diagnosis or more than one substance type; therefore, "Any" is not a sum of "Principal" and "Secondary" measures and "Total" is not a sum of "Substance type" measures.

Discussion
This study's primary contribution is the estimated total annual SUD-associated medical cost in hospitals overall and by substance type using nationally representative US hospital data. This study also provides novel prevalence and associated cost estimates of principal and secondary SUD for example, the cost of SUD treatment could be at least partially offset by a reduction in future

Limitations
This study has some limitations. These estimates reflect medical costs incurred only in hospitals.
Patients likely underreport substance use; therefore, results likely underestimate hospital costs attributable to SUD. These results do not address the cost of SUD borne by the patient and society in terms of lost quality of life and productivity. Approximately one-half of adults aged 18 years or older who reported past-year SUD also reported co-occurring mental illness. 17 Statistical methods here explicitly controlled for physical and mental health comorbidities reported on the encounter record, but the estimates may not have completely excluded non-SUD costs. This study relied on ICD-10-CM codes to capture SUD identified during the hospital encounter; however, administrative records can inaccurately capture SUD. 18 This study's cost estimates controlled for demographic, clinical, and insurance characteristics reported on the hospital discharge record, but not some important factors likely associated with encounter cost among individuals with SUD, including homelessness.

Conclusions
This study estimated the annual associated medical cost of SUD in US hospitals to be $13.2 billion.
Direct medical cost estimates can help identify cost-effective ways to prioritize prevention and treatment. The cost of effective prevention and treatment may be substantially offset by a reduction in the high direct medical cost of SUD hospital care. Hospitalizations are critical opportunities to engage patients who are at high risk for overdose to prevent future overdoses, as hospital addiction care with referral to treatment increases outpatient SUD treatment engagement. 19,20 This study's results suggest that SUD creates substantial costs for hospitals and payers, yet few hospital patients receive SUD treatment services. 4,21,22 Aligning incentives such that prevention cost savings accrue to payers and practitioners that are otherwise responsible for medical costs associated with SUD in hospitals and other health care settings may encourage prevention investment.