Article Text

Frequent callers to and users of emergency medical systems: a systematic review
  1. Jason Scott1,
  2. Annette Patricia Strickland2,
  3. Karen Warner2,
  4. Pamela Dawson1
  1. 1Faculty of Health and Life Sciences, York St John University, York, UK
  2. 2Yorkshire Ambulance Service NHS Trust, Wakefield, UK
  1. Correspondence to Dr Jason Scott, Faculty of Health & Life Sciences, York St John University, Room 311, De Grey Court, Lord Mayor's Walk, York, YO31 7EX, UK; j.scott{at}


Background There appears to be a paucity of studies examining the characteristics and impact of frequent users upon emergency medical services (EMS).

Objective To review current primary research on frequent users of EMS and to identify possible gaps in the literature.

Methods Ovid, PubMed and CINAHL/Medline were systematically searched for articles that were published in English and either referred to frequent callers to or users of an EMS, or referred to frequent users of other services where admissions were via ambulance. Studies were included regardless of quality.

Findings Eighteen studies were included. Ten were emergency department based, seven in EMS and one in a psychiatric emergency service. In emergency department studies, frequent users were more likely to arrive via ambulance than infrequent users. In EMS studies, between 0.2% and 23% of patients using EMS were frequent users accounting for 1.4% to 40% of all ambulance use. No two EMS studies used the same definition of a frequent user. No studies focused on characteristics of callers to EMS. Two studies explored interventions for frequent callers to EMS, with mixed results in reducing ambulance use.

Discussion It is unknown to what extent frequent callers impact upon EMS resources. Research should identify predictors and characteristics of frequent users of EMS, and a consistent definition of a frequent caller to or user of EMS would provide greater comparability. The lack of studies identified in this review suggests that further research is needed in order to inform policy and practice.

  • Emergency Ambulance Systems
  • Pre-Hospital

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Frequent users of healthcare services have been identified to be a heterogeneous group whose characteristics often differ to non-frequent users.1 Studies tend to focus on frequent users of emergency departments (EDs) where these patients use a disproportionate amount of resources.1 ,2 Studies that refer to frequent users as being problem users3 have received criticism for not acknowledging users’ complex needs.4 Others recognise that overuse alone is not problematic,5 and high users of the ED are high users of other healthcare services such as primary care.6 Defining a frequent user has also been difficult, with definitions being determined arbitrarily by researchers with little to no consistency or clinical justification.1 ,7 Instead a definition of five or more visits to the ED in a 12 month period has been proposed,7 although the applicability of this definition to other healthcare settings, such as emergency medical services (EMS), is unknown.

Given that EMSs are responsible for transporting a large number of patients to the ED, it is surprising that there has been little research into frequent users of EMSs. During the period April 2010 to March 2011, there were 8.08 million calls to EMSs in England alone, of which 6.61 million resulted in an emergency response.8 Of these, 4.29 million (64.9%) were conveyed to Accident and Emergency destinations.8 It is therefore possible that EMS data may provide a unique insight into frequent users of the ED, or alternatively may present a new group of frequent users who are exclusive to the EMS; in particular those who are not conveyed to Accident and Emergency.

In an ED setting it has been identified that there may be different subgroups of frequent users who are able to be identified and targeted via interventions9–11 so as to reduce the number of visits they make. At present it is unclear exactly how these subgroups are comprised, although it is believed they may be differentiated by chronic illness,12 ,13 psychiatric conditions,14 substance misuse,13 or be based upon gender, age or other demographics.1 One way in which the number of visits frequent users make to the ED can be reduced is to deliver appropriate care that incorporates the unmet needs of the patient.1

It is currently unclear if these subgroups exist in their same composition within the EMS or if other subgroups exist, therefore making it difficult to determine if such interventions would work. There has also been a call for further research into the predictors of frequent use of healthcare services,2 which supports the notion that these subgroups are not adequately defined. Current work in the UK is trying to address the issue of frequent callers to EMS.15 This systematic review is aimed to review current primary research on frequent users of EMS and to identify possible gaps in the literature.


Search strategy

A systematic search of Ovid (all years), PubMed (all years) and CINAHL/Medline (1983 to present) databases was conducted. All databases were searched and references downloaded into a bibliographical software package on 18 November 2011. Once articles had been selected for inclusion, a further reference and citation search was conducted using ISI Web of Knowledge on the 8 July 2012.

Key terms, consisting of ‘frequent’, ‘patient’ and ‘ambulance’ (see online supplementary appendix 1 for full search terms) were derived based on an iterative search of the literature on frequent healthcare users and with the assistance of the Associate Director for Quality (KW) and the Frequent Caller Case Manager (APS) at Yorkshire Ambulance Service NHS Trust.

Inclusion criteria and selection of articles

The PRISMA standards of reporting a systematic review16 were used to guide this systematic review, and all studies were assessed to determine if they met the inclusion criteria (box 1). Those identified as ‘yes’ or ‘unsure’ were then assessed by a second researcher (PD), with any disagreements resolved via discussion. Data were then extracted to assess the country of study, study design, study setting, definition of frequent, sample size, number of frequent users, number of ambulance transports, characteristics of frequent users and intervention outcomes.

Box 1

Inclusion criteria for the systematic review

  • Published in English,

  • Refers to frequent callers to or users of emergency medical services, or;

  • Refers to frequent users of other services where admissions were via ambulance

  • Primary research

Quality assessment

A spreadsheet was developed to extract data, which was refined iteratively. Quality assessment was conducted individually by JS and PD using the Manual for Quality Scoring of Quantitative Studies,17 with quality assessed by how well the aim of the article had been fulfilled. Where quality scores differed by more than 10%, JS and PD discussed where differences arose and reached an agreement on the final quality score (table 1). Due to the small number of identified studies and the research aim, all studies were included, regardless of quality. Potential bias is addressed in the discussion. Some studies required secondary analysis of their reported data to determine the total number of patients or transports. The process of any secondary analysis is highlighted at the appropriate places in the tables.

Table 1

Characteristics of included studies listed in alphabetical order


The search provided 4668 articles (figure 1), which, once duplicates had been removed, was reduced to 2409. An initial title review excluded 2217, leaving 42 articles. After full paper review, this was reduced to 16 that met the inclusion criteria. A reference and citation search for included articles identified 778 articles, of which 2 articles matched the inclusion criteria that were not previously identified.10 ,18 Eighteen studies (table 1) fulfilled the inclusion criteria with years of publication ranging from 198119 to 2012.10

Figure 1

Flow chart of literature search indicating the number of included and excluded articles at each stage of the search process.

Study designs and definitions

Eleven studies were from the USA,10 ,19–22 ,26 ,28–31 ,33 four from Australia,18 ,23 ,27 ,32 two from the UK7 ,25 and one from Taiwan.24 Ten were based in an ED,7 ,18 ,19 ,23 ,25–28 ,32 ,33 seven in an EMS10 ,21 ,22 ,24 ,29 ,31 ,34 and one in a psychiatric emergency service.20 The majority of studies used a database review,7 ,18 ,21–27 ,32 although other methods included case management interventions,10 ,28 ,31 cohort studies,13 ,30 case control studies20 ,29 and a review of medical records.19

There was no standard definition of a frequent user, although there was a preference for ED studies to use the definition of five or more visits over 12 months.7 ,13 ,18 ,26–28 No two EMS studies used the same definition of a frequent user, and none conformed to the commonly accepted ED definition of five or more visits over 12 months.1

Ambulance use in relation to the emergency department

Of the 11 studies that discussed access to healthcare other than via EMS, ten were based in the ED and one was based in a psychiatric emergency service (table 2). In the ED, frequent users accounted for between 0.1% and 16.2% of all patients attending. These accounted for between 1.9% and 20.5% of all admissions.

Table 2

Emergency department (ED) studies identifying ambulance usage of frequent users

Seven studies identified the difference in EMS use between frequent and infrequent users.7 ,13 ,18 ,20 ,23 ,26 ,27 Five found that frequent users of the ED arrive by ambulance more often than infrequent users,7 ,13 ,18 ,26 ,27 while two found that as ED usage increases, ambulance usage decreases,20 ,23 although in one of these the trend was not significant,23 and both were in a psychiatric setting.20 ,23

Four described ambulance usage during admissions to the ED by frequent users,18 ,19 ,25 ,32 which ranged from 46.1% to 84% of all attendances by adult patients. Frequent paediatric users attended via ambulance less often than adult patients, ranging between 6.4% (5–9 attendances) and 10.4% (10–19 attendances), but significantly more times than non-frequent attenders (5.6%). One study identified that a case management intervention had no impact on ambulance costs despite reducing ED attendances.28

Frequent users of emergency medical services

Seven studies (table 3) examined frequent users of an EMS,10 ,21 ,22 ,24 ,29–,31 with two of these being intervention studies10 ,31 and five which explored the characteristics of frequent users.21 ,22 ,24 ,29 ,30 From the five studies exploring characteristics, frequent users accounted for between 0.2% and 23% of patients which in turn accounted for between 1.4% and 40% of all transports via ambulance. Two studies explored callers to an EMS as opposed to ambulance transports,10 ,31 while only one study distinguished between ambulance transports and non-transports.10

Table 3

Studies identifying characteristics of frequent users of emergency medical services

Frequent ambulance user characteristics


Two studies in the USA found that frequent users were more likely to be male.21 ,29 Brokaw et al21 identified that out of 369 patients with five or more transports, 77.5% were male, while Tangherlini et al29 found that in the very highest number of transports (≥10) of 25 patients ≥65, 76% were male. Out of 235 patients transported between four and nine times, 47% were male. One further study in the USA by Broxterman et al22 found that from 1691 paediatric patients transported two or more times, 51.4% were female in comparison with 13 348 patients with single transports, of which 48.5% were female (p=0.0008).

Two further studies found no significant difference between gender and frequency of transports.24 ,30 A study in Taiwan by Chi et al24 reported on 28 716 transports, with 63.2% of men in the single-use group, 61.5% of men in the repeat-use group (2–3) and 67% of men in the frequent-use group (>3), p=0.483. A study in 2002 of 1577 elderly patients transported in the USA by Weiss et al30 identified that 58% of repeat users were female, and 57% of non-repeat users were female. Four out of 10 patients enrolled in the intervention reported by Rinke et al10 were female.


The study by Chi et al24 was the only one to identify that as frequent use increased, so did the average age of users (p<0.001). Single use patients had a mean age of 37.25±1.57 years, repeat users (2–3) 41.55±1.03 years and frequent users (>3) 46.23±1.57 years. Brokaw et al21 found that 53.7% of patients with ≥5 transports in a study examining repeat ambulance use by patients with acute alcohol intoxication, seizure disorder and respiratory illness were aged 30 years to 49 years. The average age of 84 frequent users eligible for the intervention study by Weiss et al31 in 2005 was 49±2 years, and the average age of the 10 participants in the Rinke et al10 intervention study was 60 years.

Broxterman et al22 found that in paediatric patients aged up to 21 years, number of transports by age was bimodal with peaks at <2 years and >17 years. Forty-nine per cent of repeat transports involved patients in the 17 years to 20.9 years category in comparison with 38% in the single-use category (p<0.00001). In comparison, the Tangherlini et al29 study on patients ≥65 years found that patients with a greater number of transports were more likely to be younger (p=0.007) when comparing median age and IQR of years between patients with <4 transports (78; 72–84), 4–9 transports (77; 70–84) and ≥10 transports (71; 69–75). The study by Weiss et al30 in 2002 of elderly frequent users found no significant difference between age of repeat users (75.8±7.9) and non-repeat users (76.5±13.8).


The study by Tangherlini et al29 was the only one which discussed ethnicity, and it was reported that high (4–9) and very high (≥10) frequency users were significantly more likely to be black (p=0.003) than low frequency users (<4).

Socioeconomic status

Three studies in the USA reported on measures of socioeconomic status. Tangherlini et al29 identified that as EMS use increased, frequent users of the EMS were significantly more likely to be homeless (p<0.001). More specifically, 2% of patients with a low number of transports (<4) were homeless in comparison with 12% with 4–9 transports and 33% with 10 or more transports. Broxterman et al22 reported 39% of repeat paediatric transports were funded by public insurance in comparison with 19.8% of single paediatric transports (p<0.0001). However, 45.4% of repeat transports and 60.7% of single transports were recorded as no insurance, although no inferential statistics were provided. Nine out of 10 patients enrolled in the intervention by Rinke et al10 were enrolled in a health insurance plan, seven of which were in Medicare or Medicaid.

Time of emergency medical service use

Chi et al24 found that EMS use was lowest at 16: 00 and peaked at 20:00, 13:00 and 19:00 for frequent users, in contrast to being lowest at 17:00, and peaking at 20:00, 17:00 and 21:00 for single users.

Reasons for emergency medical service use

Two studies found that frequent users were more likely to use the EMS for non-trauma events.24 ,30 Two studies also found that frequent users were more likely to use the EMS for medical conditions, which included seizure, assault, suicide attempts, abdominal or chest pain, respiratory complaints, pregnancy and mental/behavioural problems among paediatric patients,22 and cardiorespiratory, gastrointestinal and general medical problems among elderly patients.30 Acute alcohol intoxication had the greatest impact on frequent EMS use in the Brokaw et al21 study specifically comparing acute alcohol intoxication, seizure disorder and respiratory illness. Higher medical comorbidity, measured by median number of medical problems and medications, was also associated with frequency of EMS use.29 Of the 84 patients eligible for the intervention in the Weiss et al31 study, it was reported that primary problems resulting in 911 transports included cardiac (24%), asthma or COPD (25%), seizures (14%), dialysis problems (8%), alcohol problems (7%), diabetes-related problems (9%) or no contributing factors (13%).

Frequent user interventions

Two studies conducted interventions that targeted frequent users of an EMS,10 ,31 and one intervention study of frequent users of an ED reported on ambulance costs.28 All three studies (table 4) used a clinical case management approach.

Table 4

Outcomes of frequent user clinical case management on emergency medical services

Use of emergency medical services

Two studies identified the impact of a clinical case management intervention upon an EMS.10 ,31 The first study10 found that the number of transport responses and non-transport responses were significantly reduced, with a 31.6% and 79.2% reduction, respectively. The second study31 found that ambulance use increased by 56.3% in the intervention group, while it reduced by 75% in the control group. However this was a social services clinical case management intervention with an objective of increasing EMS use, as opposed to decreasing it.

Patient outcomes

One study31 identified that patients enrolled on a clinical case management intervention had a better physical score on the SF-36 health questionnaire35 than those in the control group, although there was no difference on the mental component. The other EMS study10 did not explore patient outcomes, while the study conducted in an ED setting28 reported significant improvements in psychosocial outcomes such as homelessness (57% reduction), problem alcohol use (22% reduction) and problem drug use (26% reduction), although this is inconsequential as the authors did not provide data on EMS use.

Healthcare costs

Two studies measured the associated cost savings of the intervention. One study10 reported that entire healthcare system costs associated with the frequent users were reduced by 39.2%, which once the case manager's salary had been accounted for resulted in a saving of 21%.10 The second study28 that explored costs, which focused on ED frequent users, identified a pre–post change in ambulance costs of $0. The authors did not provide a rationale for why the median post-intervention ambulance cost ($2269) was 50% of the pre-intervention ambulance cost ($1135). However, as the intervention was successful in reducing the number of attendances, the saving may have been offset by the median reduction in attendances of 40%. The intervention did make significant savings in other healthcare settings, in particular in acute settings. No further information was provided on ambulance use by the frequent users.


This systematic review aimed to review current primary research on frequent users of or callers to EMS and to identify possible gaps in the literature. The evidence base on frequent users of EMS is very limited and heterogeneous, with few studies having a primary focus on frequent users of an EMS, none exploring characteristics of frequent callers to an EMS and only two studies piloting a clinical case management intervention for frequent callers.

Definitions of what constitutes a frequent user or caller varied greatly over the studies included in this systematic review, supporting previous research based in the ED that there is a need for a common definition of frequent use.1 ,7 In the seven studies looking specifically at EMS settings, there was no consistency in definitions of a frequent user or caller with all studies using a different definition, and none adhered to the definition often used in the ED of five or more visits over 12 months.7 This made interpretation and comparison of findings difficult and suggests that the definition may not be transferrable from the ED to EMS. Further research is needed to determine the appropriate number of calls or uses of an EMS before a patient is classified as frequent.

As no studies explored characteristics of frequent callers to an EMS, the predominant method of patients accessing EMS, it is unknown if characteristics of frequent callers would differ from characteristics of the frequent users identified in this review, or how much of a burden they place upon EMS resources.

Of the studies that used EMS data, the most common finding was that frequent users of an EMS were more likely to suffer from non-trauma events, or medical conditions, than non-frequent users,22 ,24 ,30 and have a higher medical comorbidity.29 This suggests that these conditions may be poorly managed in the community or that patients with these conditions are sicker, although the lack of clarity over which conditions constitute non-trauma events differs by study and requires further exploration. The study which found that alcohol intoxication is responsible for greater ambulance use than medical conditions such as seizure disorders and respiratory illness21 leads to the suggestion that social factors are also not managed adequately in the community.

It is unclear what other characteristics, if any, are indicative of patients being more likely to be frequent users. It is however evident that frequent users of EMS use a disproportionate amount of resources. For every individual visit to the ED, a frequent user is more likely to arrive via ambulance than a non-frequent user,7 ,13 ,18 ,26 ,27 with the only exception to this being frequent users of psychiatric units, who appear to use EMS less often than non-frequent users.20 ,23 The extent of this imbalance is not fully recognised due to limitations in methods used; no studies explored characteristics of frequent callers to EMS who called for information only, or who were not conveyed to an ED. The very limited amount of studies exploring characteristics and predictors of frequent emergency medical service use hinders the ability to identify potential subgroups.

The increased use of EMS increases the burden placed upon them, limiting the available service to the rest of the community and potentially impacting upon the availability of financial resources, although the extent of which is unknown. The latter is particularly affected, as many EMSs operate a targeted response time. The UK operates an 8 min target for 999 calls to an EMS, with ambulances despatched regardless of necessity. Given that frequent users of EDs are more likely to use EMSs, this is likely to impact upon available resources.

Intervention studies based in an EMS were very limited, with patient outcomes improving and ambulance use increasing in one study,31 and calls requiring transport and non-transport were reduced while making cost savings in the other.10 The only intervention study of frequent users of the ED that disclosed EMS costs28 found that median costs reduced by 50%, although there was no significant difference due to a wide CI. No ED studies reported the impact of an intervention on EMS use. Any future research of interventions in EDs should explore the impact on other healthcare services associated with the ED, including the EMS. Furthermore, following criticisms of using response times as performance indicators,36–38 attempts to develop more appropriate clinical performance indicators39 ,40 should explore how frequent users may impact upon them.

Limitations of included studies

The scope for publication bias in the presenting of findings of frequent users to EDs should be noted. Of the 25 studies included in a systematic review of frequent users of the ED published in 2010,1 only two13 ,26 discussed ambulance use and were thus eligible for inclusion in this systematic review. It is possible that authors of the other studies did not collect or disclose EMS usage among their sample of frequent users. In one study included in this review,27 the authors did not fully disclose how many frequent users attended via ambulance, instead only discussing the percentages, not actual numbers from two of the six age groups. One criticism of interventions focused on EDs is that they may miss patients who attend multiple EDs.1 In the UK, and possibly elsewhere, the use of EMS data to identify frequent users may help identify these patients, provided they were attending the ED via ambulance.

A further limitation of included studies is the low average quality score (64.5%). This does not necessarily indicate that research on this topic has been of low quality. It is possible that these scores represent the difficulty of conducting research in an EMS setting where the majority of articles rely upon data collected for the purpose of monitoring and improving services, rather than specifically for research.

Limitations of this systematic review

The use of a single reviewer at the beginning of the assessment process has been suggested to introduce bias into systematic reviews. We overcame this limitation by involving all four researchers in the development of the search terms, and having a second reviewer assess records that were deemed ‘unsure’. The primary researcher (JS) erred on the side of caution when assessing records. The use of a bespoke checklist41 and following PRISMA guidelines helped to further reduce the impact of this limitation. We also recognise that the use of an iteratively developed data extraction spreadsheet could be seen as a limitation, though this has been suggested to be an accepted practice in systematic reviews depending upon available resources and data needs.42


This systematic review identifies that there is currently very little research exploring characteristics of frequent users of EMS, and none exploring characteristics of frequent callers into an EMS. Frequent users of EDs are more likely to arrive via ambulance than non-frequent users, while frequent users of EMSs are more likely to suffer from medical conditions than trauma events. As no studies explored characteristics of frequent callers to EMSs, the primary method of accessing the service, it is unknown to what extent frequent callers impact upon an EMS. Clinical case management interventions may be able to reduce transport and non-transport requiring calls, but further research is needed to determine their suitability. Research should also identify predictors and characteristics of frequent users of EMSs, particularly using EMS call data, which would enable cost-effective care to be put in place to avert overuse of EMS when other interventions may be more appropriate. Furthermore, a standardised definition of frequent callers to and users of EMSs is required.


We would like to express our gratitude to Dr Anna Jones and Dr Stephanie O'Neil for providing comments and feedback on early drafts of the manuscript.


Supplementary materials

  • Supplementary Data

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  • Contributors JS was involved in the conception, design, analysis, interpretation of data and drafting the article. APS and KW were involved in the conception, interpretation of data and critically revising the manuscript. PD was involved in conception, design, analysis, interpretation and critically revising the manuscript. All authors provided final approval of the version to be published.

  • Funding Yorkshire Ambulance Service NHS Trust.

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement The authors have included all of the original search terms in the online supplementary appendix and are happy to share them. No additional data is available.