We sought to describe the referral pattern to, and between, the medical specialist outpatient clinics in the University Hospital of Southern Denmark. Our study showed that referrals were evenly distributed between hospitals 49.5% (233) and GPs 50.5% (238), with a very small percentage either attending another speciality or simultaneously referred. Of the referrals from hospitals, one-third (72) were from the Medical Department (internal referrals). This may reflect an inefficient referral process within the department. Of these, inter-departmental referrals accounted for 70% (51) and inter-speciality referrals accounted for 30% , meaning that some of the outpatient clinics in the Medical Department referred patients to themselves (self-referral) e.g. pulmonology outpatient clinic referring the patient to their own clinic. Interestingly, day hospital and pulmonology outpatient clinics received the majority of the referrals from internal sources, whereas cardiovascular and pulmonology outpatient clinics received the majority of the referrals from external referral sources.
There is considerable information on referral from GPs in the primary care sector to secondary care internationally [13, 15,16,17,18,19, 23]. Unlike in the current study, these studies [18, 19, 23] showed that the majority of referrals came from GPs. Based on the aforementioned findings that GPs often refer patients according to their symptomatic picture rather than with a confirmed diagnosis [17, 24, 25], we expected that our findings would also comprise of a considerably higher proportion of patients referred from GPs. Additionally, the finding that the Medical Department also had considerably higher proportions of inter-departmental and inter-specialty referrals was unexpected. We propose several reasons for the increased proportion of inter-departmental referrals in our study, including increasing numbers of patients with multi-morbidities that require complex care from several specialists [7, 8] and the internal referral procedure at the Medical Department between the outpatient clinics. However, the unusually high rate of inter-departmental referrals requires further investigation. Furthermore, many previous studies of referral have tended to use self-reported data or survey formats [19, 20, 26,27,28] to describe referral patterns and examine factors influencing healthcare professionals’ referring habits [4, 29]. There is a possibility that these previous findings may have been impacted by recall bias. Use of register data provides more accurate findings.
Despite the growing awareness of issues related to referrals, there has been relatively little research internationally on referrals between specialists in hospital outpatient clinics or departments. The literature on referral is diverse and differences in contexts, study methods, and measurement of referral patterns make it difficult to compare results between studies. Similar to our study aim, a qualitative study by Burkey et al.  on inter-departmental referrals in a hospital indicated that inter-departmental referrals are likely to increase among specialists. Multi-morbidity may explain the same. Furthermore, inefficient referral processes have been considered to play a role in unnecessary referrals resulting in patients undergoing unnecessary diagnostic procedures [10, 11].
The Medical Department at The University Hospital of Southern Denmark in our study is a typical representation of hospitals on an international level that face similar challenges of increasing demands and limited resources. It receives a high proportion of inter-departmental and inter-speciality referrals. It is difficult to explain what causes the inter-speciality referrals. However, a subjective reflection based on clinical experience from the chief consultant and manager of the Medical Department, suggests that the inter-speciality referral or self-referring is often associated with outpatient clinics that are organised into small specialised teams or clinics that have local functions at the hospital’s other facilities. As a result of the organisational system and varying models of care within the same department, the physicians occasionally send formal referrals to their own outpatient clinic when patients require other services from a different team, instead of booking the patient directly for the next appointment. This is further illustrated in that the day hospital received the majority of the referrals from internal sources. Additionally, less experienced or junior physicians may feel more compelled to refer patients through the formal channels because they may be unfamiliar with the referral procedure. In future research, it would be very interesting to investigate in-depth the differences between e patients being referred internally compared to those being referred from external sources.
Unnecessary referrals may increase the cost of providing care, consuming healthcare resources that could have been used to provide other services . For example, the practice exacerbates the administrative workload for the healthcare professionals and administrative employees such as secretaries that are responsible for screening and sending referrals as well as booking tests for the preliminary appointments. Costs for patients may include delayed treatment and waste of time  related to unnecessary patient appointments and repetitive tests [10, 11]. Visiting hospitals several times a year for further assessment could subject patients to stress and affect their mental well-being [14, 31].
A new way of managing referrals is required in the hospital system. Several strategies can be implemented to improve the referral process within the Medical Department, and thereby, reduce high inter-department and inter-speciality referral rates. Measures such as IT-solutions , joint triage of referrals [12, 33,34,35], and co-location [36, 37] of the medical outpatient clinics to create a joint medical outpatient clinic could provide opportunities for inter-professional collaboration due to close physical proximity. Close proximity may stimulate more informal consultation between medical outpatient clinics replacing formal referrals. This would allow specialists to work together availing of information-sharing and diagnosing and treating mutual patients. IT-software can be used to gain an improved overview of patient flow and management [38, 39]. The University Hospital of Southern Denmark already uses IT-software for management and workflow on in-patient wards. Similarly, healthcare professionals in outpatient clinics could use IT-software to communicate with each other and book patients directly for appointments and tests thus, improving the inter-departmental and inter-speciality referral process [38, 39]. Added benefits to using IT-software are easier to locate colleagues and fewer interruptions. Co-location, in combination with IT-software and joint triage of patient referrals, could provide patients with convenient access to necessary diagnostics and allow for same-day treatment from several providers simultaneously. This could reduce ineffective use of physician and hospital services allowing patient care in hospitals to be organised around patient needs rather than the needs of medical specialties involved. Additionally, it may ensure improved workflow and safe ongoing care.
Implications for practice and future research
We anticipate that our results will be useful for clinicians, managers, decision-makers, and researchers in understanding and improving referral processes. Our study sheds light on potential inefficiency in referral processes within a hospital, which can be explained by the organisational structure and the administrative system. Our findings could stimulate similar practices and hospital systems nationally and internationally to conduct an assessment of their current referral and routine practice to minimise unnecessary referrals and improve inter-departmental collaboration between specialists. The findings may also help guide strategies for quality improvement and serve to initiate discussions on how care of patients between multiple outpatient clinics within a single hospital system is best organised.
Strength and limitations
While the size of the study was comprehensive, the study was limited to a short period of time and a single health service in a region of Denmark, which may limit the generalisability of our results.
Due to the availability of the data, it was not possible to examine the differences between the sub-groups within the external referral category, which include referrals from different organisations (GPs and hospitals). It would be interesting to investigate how referrals from primary care differ from hospital referrals to the medical department as hospitals are highly specialised in comparison to primary care. GPs generally refer patients to specialised care for diagnostic reasons, whereas referrals from highly specialised hospitals to other specialised hospitals may be part of an on-going treatment plan or a transfer of a patient. Thus it is conceivable that referrals from hospitals are more precise compared to referrals from GPs. It may be possible that the referrals from GPs are completed, to a greater extent, after the first consultation. To improve the referral process, future studies should investigate the characteristics of each of the referral processes.
Additionally, the number of internal referrals may be due to organisational factors, local practices and different models of care and could be resolved by multi- and interdisciplinary care.
A strength of our study is that we used registry data: the Danish hospitals routinely collect data linked to the 10- digit personal identification number (CPR number) and hence provide highly valid and reliable data for research.