Introduction and geographic disparity of consultation-liaison psychiatry in Japan: Retrospective analysis of data from the Japanese National Inpatient database.

Background: Consultation-liaison psychiatry (CLP)—professional psychiatric care provided to coordinate with surgical or medical treatment of inpatients with psychiatric disorders—was included in universal health coverage in Japan in 2012. Despite evidence of benets of CLP, basic data and geographic distribution information regarding CLP at the national level remain unclear. This study aimed to identify the clinical features and geographic disparity of CLP provided in Japan. Methods: We retrospectively analyzed anonymized data retrieved from the Japanese administrative inpatient database regarding inpatients who were provided CLP between April 2012 and March 2017. Demographic characteristics were summarized and geographic disparity by prefecture was visualized for scal years 2012 and 2016; we also summarized the data with descriptive statistics according to region. Results: Data from a total of 46,171 patients who received 138,866 CLP services were included. Results revealed more patients aged 75–84 years received CLPs than any other age group (29.7%) and the overall male/female ratio was 53:47 in 2016. In 2012 and 2016, 24.2% and 30.7% of CLP patients, respectively, were transferred to other hospitals; 9.7% and 8.8%, respectively, discharged due to the death. CLP services were provided in 14 prefectures in 2012 and 33 by 2016; 14 prefectures had no available CLP services. Conclusions: Our study claried the characteristics of patients in Japan who received CLPs and the geographic disparity in CLP services. Although ve years had passed since CLP was introduced, the results imply wide availability of CLP nationally. The analysis data provided may inform future policies to improve CLP services.


Data source
This was a retrospective, observational study that used data from the Japanese Administrative Database; the Diagnosis Procedure Combination per-diem payment system (DPC/PDPS) (details of the DPC/PDPS have been described elsewhere) (18,19). Brie y, the DPC/PDPS is a case-mix patient classi cation system that is linked to payments at acute-care and mixed-care hospitals in Japan. By 2016, the DPC/PDPS-based hospital reimbursement system had been adopted by more than 1600 hospitals, which accounted for more than half of the total 894,000 hospital beds nationwide.
Anonymous clinical and administrative claims data were collected annually for patients from the participating hospitals. Clinical data consists of baseline patient information, diagnosis (based on ICD-10), and detailed medical information such as all major or minor procedures, medication, and device use. The database also includes the purpose of admission, discharge destination, and outcome at the time of hospital discharge. Hospital information is also collected under the DPC/PDPS. We obtained population data according to prefectures from a national survey called Population Estimates (20). Each region consists of several prefectures. This study was approved by the Institutional Review Board at the Tokyo Medical and Dental University and the National Center for Child Health and Development. The board waived off the requirement for patient informed consent because of the anonymous nature of the data.

Participants and variables
We identi ed patients who had received CLP (Japanese code: A230-4) between April 1, 2012, and March 31, 2017, from the DPC database. We excluded 224 patients with 397 CLP services from one hospital due to not having complete hospital information. Data pertaining to individual-level characteristics were extracted. Individual variables included age, sex, admission status (planned, unplanned, or urgent), discharge settings, discharge outcome, and disease classi cation according to ICD-10. Age was categorized into six groups: 0-29, 30-49, 50-64, 65-74, 75-84, and 85+. Disease classi cation was categorized according to ICD-10 Chapter numbers from "I "(Certain infectious and parasitic diseases) to "XXII' (Codes for special purposes). Data regarding in-hospital psychotherapy were also obtained from the database. In-hospital psychiatry was recorded in the administrative database a maximum of three times per week due to the limitations of the payment system.

Statistical analysis
Continuous variables were summarized with the use of descriptive statistics (mean ±standard deviation for values with normal distribution, and the median with interquartile range (IQR) for values with non-normal distribution), and categorical variables were summarized as frequencies and proportions. All statistical analyses were performed using R statistical software, version 3.3.2 (R Foundation for Statistical Computing, Vienna, Austria), and data visualization were performed by Tableau Software version 2018.3 (Tableau software, Seattle, United States of America).

Patient and hospital characteristics
A total of 46,171 patients who were provided CLP quali ed based on the inclusion criteria. Table 1 shows the basic characteristics of those patients and hospitals. The age group who used the services the most included those patients aged 75-84 years (29.7% in 2016). About half of all patients were female (47.2% in 2016), and the proportion of patients whose CLP-related medical care was unplanned or urgent was 67.8% in 2016. Also in that year, 109 hospitals in Japan provided CLPs. The number of provided CLP services, patients who received CLP, and hospitals providing CLP increased almost three-to four-fold in between 2012, when CLP was introduced, and 2016 (428%, 406%, and 363%, respectively).
The characteristics of patients' discharge settings and outcomes as of discharge were also shown in Table 1. More than half of the patients were discharged and followed-up by outpatient services (53.3% in 2016), while about nearly one-third of the patients were transferred to other hospitals (30.7% in 2016) and 5.1% of were transferred to welfare facilities in 2016. Overall, the in-hospital mortality ratio for the patients who received CLP services was about 9 percent (8.8% in 2016).
Characteristics of disease classi cation by cost (in terms of all resources), or "most resource-consuming diagnosis," of study cohorts are summarized in Table 2. The highest proportion of disease classi cation was "neoplasm" (22.9% in 2016), followed by "disease of circulatory system" (16.7% in 2016), "injury, poisoning and certain other consequences of external causes" (13.7% in 2016) and "other" classi cations.
The provision of in-hospital psychotherapy in the study cohort was summarized in Appendix 1. About three-tenth of the patients did not have in-hospital psychotherapy (31.9% in 2016), while about one-fth of the patients had just one in-hospital psychotherapy (19.5% in 2016). Almost half of the patients had several in-hospital psychotherapy sessions, and 13.9% of the patients had more than six psychotherapy sessions in 2016.  Table 3 also shows descriptive statistics of CLPs by region. There was no hospital providing CLP services in the Shikoku area until 2014 (data not shown), while more than one-third of the CLP services provided in 2016 were in the Kanto area. The provided CLP services per population ratio showed wide variation even in the regional area level (range: 0.19-0.54 CLP services per thousand population).

Discussion
The present retrospective study investigated the national-level CLP service in general hospitals in Japan, using a national inpatient database. The present study characterized (1) the key overview of patients who received CLP services and (2) the geographic disparity of these patients. To the best of our knowledge, this article is one of the rst reports revealing CLP disparity. In today's current health care climate of cost savings, limited allocation of resources, and expectations of demonstrations of the value of services and clinical productivity, it is important to clarify the current situation regarding CLP services to understand how to make for future improvements to the healthcare system.
After the introduction of CLP services in 2012, the provision of CLP was consistently increased (Table 1), implying the recognition of the need for CLP services in medical and surgical patients. Also, almost 70% of patients we studied who received CLP services were over the age of 65 in 2016, which was much higher than in recent studies in a Canadian setting (roughly 42% from two academic tertiary care hospitals) (21) and an Italian setting (mean and SD age was 57.9 ±19.4 from one general hospital) which were in line with other reports from Europe in terms of demographic data (about 41%) (22). We speculated that this is due to the difference in the aging ratio of the study population, criteria for referral, priority/availability for CLP referral, and the healthcare system. Our results also showed that about 70 percent of CLP services were provided to patients whose admittance was unplanned or who were admitted due to an urgent condition. This is partly because such patients may not have been prepared for, or may be especially agitated about, their health problems compared with planned admission patients.
While data regarding discharge settings and outcomes were usually unavailable internationally, it was reasonable that about three out of every ten patients who received CLP were transferred to other hospitals (Table 1), which is much higher than the 5.8-7.5% overall average of acute-/mixed-care inpatients in a Japanese setting (23). We speculated that some of the patients with psychiatric comorbidities were transferred to psychiatric hospitals (detailed data about discharge settings were not available). It was surprising that about nine percent of patients who received CLP services were discharged as dead (Table 1), which was also much higher than the overall average of 1.7%-3.3% (24). We also speculated that some CLP services were provided for severe patients who needed psychiatric support for improving their mental condition as a part of end-of-life care. However, further studies are required to address this issue due to data unavailability.
It was reasonable that more than one-fth of CLP services were provided to the cancer patients, considering both the number of cancer inpatients (13.4% in general hospitals) (25) and that approximately 29-43% of these patients ful lled the diagnostic criteria for having a psychiatric disorder (26,27) (Table 2). However, in terms of international comparisons of CLP data, it is not easy to compare in detail. For example, few data were available in the basic disease classi cations of the study cohorts. Even if data were shown, as in the Canadian study (21), it may not be easy to compare with our data due to the absence of consensus in disease classi cations for CLP cases. Another example is that our data pertaining to the reasons for CLP referrals (psychiatric diagnosis) are not available, as they were for a previous study (21,28), because the DPC database was not designed for speci c studies but various research elds. Further efforts for international collaborative research will help improve the quality of available evidence.
Almost 70% of patients who received CLP services used in-hospital psychotherapy; the rests did not use in-hospital psychotherapy (Appendix 1). This is partly because some CLP services were provided to patients with postoperative delirium which usually disappeared in a short period (i.e., a week), who usually did not need in-hospital psychotherapy. Although the distribution of the number of provided in-hospital psychotherapy sessions was right-skewed, there was another peak in "six and over" during hospitalization. These patients would be those with severe psychiatric conditions or longer lengths of stay. Another possibility is that there was a lack of in-hospital psychiatry in some cases, especially in hospitals where psychiatric healthcare resources are scarce. This is one of the further questions to be addressed. CLP in Japan started from selected prefectures and gradually spread throughout Japan; however, there are still 14 prefectures where provided no CLP services with their own in 2016 (Figure 1). In addition, there is a variation in providing CLP services even in the regions (Table 3). Although 5 years had passed from the introduction of CLP, there is still geographical disparity of CLP services, which needs to be improved. It is similar in the United Kingdom, where studies identi ed widespread availability of liaison psychiatry services in acute care hospitals (29). Investigation in the current/future needs of CLPs and enhancing/expanding the delivery system of CLPs would be considerable. Further efforts for improving geographic disparity is needed for achieving e cient care in CLP services for those who needed care.
This study has major strengths: it is the largest reported study on this subject in terms of patient numbers in a Japanese setting based on a national administrative database. According to the National Database Open Data, the analysis covered more than 92% of the CLPs in Japan (30). Further, to our knowledge, this study was the rst report which reveals fundamental information of CLP services and geographic disparity in CLP services in Japanese setting which were essential for enhancing the quality of life of patients and improving e ciency in the healthcare delivery system. Thus, our results could inform future interventions to improve medical services and the provision of healthcare.
Several limitations of the present study must be considered. First, this investigation was based on an administrative database (DPC). The database covers more than 93% of CLP services conducted across Japan; however, a few hospitals do not participate in the DPC/PDPS system and the exclusion of these hospitals may have introduced an element of sampling bias.
Second, data pertaining to several important variables are not available in the DPC database. Therefore, factors such as the difference in psychiatric diagnosis before and after CLP, reason for CLP referral, timing of CLP, detailed interventions in CLPs, and degree of psychiatrists' pro ciency were not included in the analysis.
Third, the present study did not analyze patient outcomes. Although previous researches had reported the bene t of CLP services (10)(11)(12)(13)(14), further outcome studies based on a DPC database would be preferred.

Conclusions
Data regarding CLP services at the national level had not been analyzed and organized in a way that makes it usable for patients, health care providers, or policy administrators. Our present study revealed the fundamental information and geographical disparity in CLP services in Japan. These results can inform hospital administrators and health service providers improvement the equity of the provision, e ciency of service, and policies relating to healthcare involving CLP. Further research is also needed comparing outcomes of qualifying patients who receive CLP with those who qualify but do not receive these coordinated services and to compare availability, insurance coverage, and utilization of CLP in other countries.

Declarations
Ethics approval and consent to participate This study was approved by the Institutional Review Board at the Tokyo Medical and Dental University and the National Center for Child Health and Development. The board waived off the requirement for patient informed consent because of the anonymous nature of the data.

Consent for publication
Not applicable.

Availability of data and materials
The data availability is not applicable due to an ethical restriction. However, data will be made available by the DPC research group for researchers who meet the criteria for access to these con dential data. Request to access the data should be submitted to the corresponding author.

Competing interests
The authors declare that they have no competing interests.

Funding
This study was supported by a Grant-in-Aid for Research on Policy Planning and Evaluation from the Ministry of Health, Labour and Welfare, Japan (H29-Seisaku-Shitei-009), a Grant-in-Aid for Young Scientists (B) from the Japan Society for the Promotion of Science (JSPS KAKENHI, 16K19284). The Foundation has had no in uence in the design of the study, data collection, analysis or interpretation of data, publication of results or writing this manuscript.

Authors' contributions:
DS participated in study design, analysis and interpretation of data, drafting the article, and revising the article for intellectual content. NI, HT and KMS participated in study design, interpretation of data, drafting the article, and revising the article for intellectual content. KFj and KFs participated in study design, interpretation of data, and revising the article for intellectual content. All authors read and approved the nal manuscript.