Appendix 1.

Characteristics of the studies included in the scoping review (n=63)

First author and reference	Year	Country	Type of study	Objective
Abate, B[24]	2010	Ethiopia	Mixed-methods retrospective	To assess information use in patient’s referral system, current referral process, and problems associated with documentation.
Abodunrin, OL[25]	2010	Nigeria	Cross-sectional	To determine the awareness and perception of adult residents in Ilorin toward the policy on appropriate utilization of levels of health facilities through referral system.
Abrahim, O[2]	2015	Ethiopia	Cross-sectional	To examine what percentage of patients had either sought prior care or had been referred to the present facility and identify demographic and clinical factors associated with having sought prior care or having been referred.
Afsar, HA[26]	2003	Pakistan	Cross-sectional	To estimate the proportion of patient referral and to identify the factors associated with unsuccessful referral in Karachi, Pakistan.
Akande, TM[27]	2004	Nigeria	Cross-sectional	To examine referral system in Nigeria with a study on new patients seen in a tertiary health facility.
Alkinaidri, A[28]	2018	Saudi Arabia	Case study	To explore using Lean Six Sigma as a way to improve healthcare referral system.
Alshami, M[29]	2014	Saudi Arabia	Case study	To report on the experiences of implementing the EHALA electronic referral system at a local Saudi hospital.
Amoah, PA[30]	2017	Ghana	Qualitative deductive approach	To examine how the resources embedded in both structural and cognitive aspects of social relationships influence knowledge of, and adherence to, referral policy.
Bailey, PE[17]	2019	Ghana	Secondary analysis	To assess the relationship between referral and facilities’ readiness to treat complications at each level of the health system in Ghana. Also investigate other facility characteristics associated with referral.
Belway, D[31]	2008	Canada	Retrospective, stratified cohort	To determine the association between transport intervals and intensive care unit (ICU), and hospital length of stay and hospital mortality at the receiving hospital.
Bossyns, P[32]	2006	Niger	Cross-sectional	To establish a benchmark for referral rates in rural Niger so as to allow interpretation of routine referral data to assess the performance of the referral system in Niger.
Calfee, RP[23]	2012	USA	Retrospective cohort	To systematically examine the impact of insurance status on access to and utilization of elective specialty hand surgical care.
Chambers, EC[33]	2015	USA	Quasi-experimental	To examine the effectiveness of referring patients with prediabetes and determine whether referrals were sustained after the intervention.
Clarke, A[34]	2010	USA and UK	Systematic review	To assess effectiveness of guidelines for referral of elective surgical assessment.
Daniels, AA[35]	2020	Ghana	Qualitative	To examine the lived experiences of patients, healthcare providers, and relatives of patients on the referral system.
Dennison, J[10]	2006	UK	Pilot	To assess the effect of the electronic surgical referral service on patient waiting times and attendance rates.
Dogba, M[36]	2011	Mali	Cross-sectional	To assess, in women presenting with an obstetric complication: 1) the effects of the point of entry into the referral system on joint mother-newborn survival; and 2) the effects of the configuration of healthcare team at the CHCs on joint mother-newborn survival.
Doumouras, AG[37]	2017	Canada	longitudinal analysis	To determine the impact on referral rates to bariatric surgery after converting to an online referral system from a fax-based system.
Ebrahimiadib, N[38]	2016	Iran	Prospective observational	To compare the efficacy of an internet-based versus traditional referral system for retinopathy of prematurity (ROP) screening in Iran.
Esan, O[16]	2016	Nigeria	Cross-sectional	To observe the prevalence of deficiencies in the referral letters to a department of psychiatry in a Nigerian teaching hospital.
Eskandari, M[19]	2013	Iran	Qualitative	To describe barriers of health-care process in rural societies in Iran.
Fernández-Méndez, R[39]	2020	UK	Retrospective cohort	To determine the impact of introducing a Web-based, electronic referral (eReferral) system to a specialized neuro-oncology center, using a service-developed proforma, in terms of waiting times and information completeness.
Fyie, K[21]	2014	Canada	Mixed-methods retrospective	To describe referral processes and practices, and their impact on the waiting time from referral to consultation for TJA.
Give, C[40]	2019	Mozambique	Qualitative	To explore barriers and enablers of referral within the lens of complex adaptive health systems.
Handayani, PW[8]	2018	Indonesia	Quantitative data processing	To identify a user acceptance model for the health referral system in Indonesia.
Hill, VA[41]	2000	UK	Quasi-experiment	To undertake an audit to assess the impact of the guidelines with a follow-up audit in 1995
Idowu, AO[42]	2018	Nigeria	Retrospective	To ascertain the frequency of requests for endocrine consultations, to determine the sources of consults, the common cases referred, the reasons behind consultations, and the outcome of patients who benefited from endocrine consultations.
Islam, S[43]	2015	Bangladesh	Retrospective cohort	To assess the patient referral system in the urban DOTS programme in Dhaka, Bangladesh, with a view to identifying problems and solutions.
Jaturapatporn, D[44]	2006	Thailand	short article	To present the current situation of family medicine in Thailand.
Kalhor, R[45]	2014	Iran	Cross-sectional descriptive	To investigate human resources situation of the family physician program in 6 pilot cities in Khuzestan province in the southwest of Iran.
Kavosi, Z[46]	2018	Iran	Cross-sectional	To evaluate the overall performance of the referral system in Fars Province in 2015.
Kennedy, A[20]	2012	UK	Cohort	To adapt the 2002 Scottish Referral Guidelines for suspected squamous cell carcinoma of the head and neck (SCCHN) as a set of “alarm symptoms.”
Khayyati, F[22]	2011	Iran	Quasi-experiment	To evaluate the impact of the program on accessibility of the services, case finding, patient referral, feedback process and insurance coverage in the rural health units.
Kim, E-H[47]	2010	USA	Survey	To present findings and observations on the factors affecting the clinical acceptance of our web-based referral system.
Kim, Y[18]	2009	USA	Survey	To assess the impact of electronic referrals on workflow and clinical care.
Kim-Hwang, JE[48]	2010	USA	Quasi-experiment	To determine the impact of eReferral (compared with paper-based referrals) on specialty referrals.
Kongnyuy, EJ[49]	2008	Malawi	Retrospective review	To obtain feasibility of using criteria-based audit to improve a district referral system.
Li, C[50]	2011	China	Literature review	To examine the health insurance reform experiences in Thailand with respect to the objective of universal coverage and attempt to draw out some lessons for China, taking into account China’s practical context.
Lim, K[51]	2018	Korea	Survey	To examine the current hospice referral scenario for terminally ill cancer patients and create a data form to collect hospice information and a modified health information exchange (HIE) form for a more efficient referral system for terminally ill cancer patients.
MacGregor, D[11]	2009	Canada	Pilot	To evaluate the implementation of a web-based referral system
Majoko, F[52]	2005	Zimbabwe	Cohort	To determine the prevalence of antenatal and intra-partum referrals, compliance with advice and perinatal outcomes in referred pregnant women in Gutu district, Zimbabwe.
Mehet, J[53]	2018	UK	Review	To explore the literature evidence surrounding the clinical impact of the NORSe referral system and analogous models.
Nsigaye, R[54]	2009	Tanzania	Qualitative	To design and assess a referral system to link persons diagnosed at a voluntary counselling and testing (VCT) clinic in a rural district in northern Tanzania with a government-run HIV treatment clinic in a nearby city.
Oates, J[14]	2000	Canada	Observational cohort	To assess the association between patient-centered communication in primary care visits and subsequent health and medical care utilization.
Oliva, X[55]	2013	Spain	Survey	- To improve the resolution of endocrine diseases in primary care - To decrease inadequate visits to specialized care
Omole, VN[6]	2017	Nigeria	Cross-sectional	To probe for information toward improving the quality of the referral process and the health system
Prathiba, P[56]	2020	India	Descriptive	To assess the gaps in the referral of patients from primary care arriving at the obstetric EMS of a tertiary hospital.
Prinja, S[57]	2014	India	Time series analysis	To evaluate the referral transport system in Haryana
Quinn, GP[58]	2011	USA	Pilot	To develop a referral system to increase the likelihood that patients of childbearing age with newly diagnosed cancer receive timely information about fertility and reduce the burden oncologists may feel when discussing and exploring fertility preservation options with their patients.
Scheibe, MM[59]	2015	USA	Retrospective	To evaluate the use and impact of a novel electronic referral (eReferral) system in rheumatology in a safety net health system.
Shams, A[60]	2013	Iran	Descriptive analytic	To determine factors affecting the fulfillment of referral system process
Shephard, E[15]	2018	UK	Survey	To improve patient safety and junior doctor efficiency in the referral process.
Tuot, DS[61]	2015	USA	Quasi-experiment	To examine how specialists leverage an electronic referral and consultation system to deliver specialty care.
Williams, L[62]	2012	Ireland	Survey	To improve patient care by reducing unnecessary outpatient visits, avoid emergency department presentations, shorten waiting times, and alleviate the administrative burden on healthcare staff.
Woodward, M[12]	2020	UK	Quasi-experiment	To apply a human factors/ergonomics (HFE) approach to place analysis of local workflow and user engagement central to the development of a new regional electronic referral system.
Yu, W[63]	2017	China	Survey	To explore the effect of doctors’ and patients’ practices and attitudes on their willingness for downward referral and the relationship between downward referral and sociodemographic characteristics.
Zanolini, A[64]	2016	Zambia	Pilot	To pilot a peer referral intervention in which circumcision clients were offered incentives for referring their peers for circumcision.
Zhang, X[13]	2018	China	Cross-sectional	To identify the key nodes that affect patient satisfaction during the referral service process.
Kamau, KJ[5]	2017	Kenya	Cross-sectional	To establish challenges facing implementation of the referral system for quality health-care services in Kiambu County, Kenya.
Chitsa, B[65]	2019	Malawi	Qualitative	To investigate the factors that affect management of the referral system at the primary level of health-care in Zomba district in Malawi.
Chiou BL[66]	2020	Taiwan	Retrospective cohort	To explore the economic burdens of hip fracture surgery in patients referred to lower-level medical institutions and to evaluate how referral systems affect costs and outcomes of hip fracture surgery.
Corwin P[67]	2014	New Zealand	Quasi-experiment	To assess whether feedback improves the quality of referral letters from general practice to secondary care and how electronic referrals affect the quality of referral letters.
Jiwa M[68]	2004	UK	Non-randomised control trial	To determine if written feedback about the contents of GP referral letters mediated by local peers was acceptable to GPs and how this feedback influenced the content and variety of their referrals.
Azamar-Alonso, A[9]	2019	Canada	Scoping review	To review the evidence base for the effectiveness and cost-effectiveness of eReferral systems.