Introduction
In type 1 diabetes, there has been a shift from traditional methods of self-monitoring of blood glucose using fingerpricks and glucometers (compliance can be poor with <50% adherence to guidelines among people with type 1 diabetes in Sweden [
1]) to using new technologies that allow for more frequent measurements with less discomfort. These new technologies enable real-time or intermittently scanned continuous glucose monitoring [
2]. The latter is known as flash monitoring, with the only system currently available for use in the National Health Service (NHS) in the UK (including Scotland) being Abbott’s Freestyle Libre. Flash monitors (FMs) have been available in the UK since late 2014 [
3]. They became freely available in Scotland from the NHS in 2018, having been only self-funded previously. Eligibility for FM use follows a mixture of criteria defined by each of the Scottish Health boards.
The largest RCT of FMs (
N = 328), IMPACT, demonstrated a significant effect of FM use on hypoglycaemia without any significant change in HbA
1c. However IMPACT was restricted to adults with good glycaemic control (HbA
1c ≤ 58 mmol/mol [7.5%]) [
4], and is therefore not representative of the range of current recipients of this technology from the NHS. Observational studies have shown reductions in HbA
1c, diabetic ketoacidosis (DKA) and hypoglycaemia with use of FMs [
5‐
14]. Greater effects on HbA
1c have been found in individuals with high initial HbA
1c but, apart from this, study of variation in effectiveness across different subgroups of recipients has been limited, particularly for DKA, where there is a gap in the literature. It is important to determine whether any groups benefit less from FMs, as this may indicate a need for measures to improve efficacy.
In this paper, we aimed to describe the contemporary prevalence of FM use among all those with type 1 diabetes in Scotland and to examine the association of FM initiation with glycaemic outcomes (HbA1c, DKA and hypoglycaemia) across the full range of recipients and within age, sex and socioeconomic groups, as well as by prior glycaemic control, insulin pump usage and completed diabetes education programme. We also examined outcomes among the early adopters, who self-funded the device before it became NHS-funded.
Discussion
This study showed that prevalence of FM use increased rapidly among individuals with type 1 diabetes in Scotland after FMs became free of charge but disparities remain across deprivation levels. FM initiation was associated with a significant decrease in HbA1c overall among users. HbA1c reductions were most pronounced in those with high baseline HbA1c. HbA1c reductions occurred in all SIMD quintiles and age groups, and regardless of sex, prior pump use, early adopter status or prior completed diabetes education programme. FM use was associated with marked reductions in DKA overall and generally within all subgroups examined. FM initiation was also associated with a decrease in SHH among those with a prior history of SHH.
To our knowledge, our large nationwide study is the first to examine disparities in the prevalence of FM use in Scotland. We have confirmed and extended previous glycaemic outcome findings of small-scale studies in Scotland [
6,
22] by providing generalisable results. We have also augmented the scope of recent large-scale studies [
13,
14] by extensively exploring variations in HbA
1c and DKA outcomes following the initiation of FM use across sociodemographic strata, which has not been done before and provides novel information crucial to clinical practice.
Efforts made by the Scottish Government, clinical teams, charities such as Diabetes UK, and people with diabetes to widen the usage of FMs in Scotland have been successful, with a tenfold increase in use over the past couple of years. However, the gap between most- and least-deprived quintiles persists, although it is smaller than the 4% vs 60% observed in the most- vs least-deprived quintiles in an Edinburgh diabetes centre in 2017 prior to NHS funding [
3]. This gap highlights the existence of healthcare inequalities in access to technology. The extent to which this relates to user preference or to failure of the devices being recommended by clinicians is unclear. Prevalence of use is highest among the paediatric population but gaps across deprivation levels exist even in this group.
Our overall findings on HbA
1c reductions are in keeping with previous findings such as those from a single-centre Edinburgh study (−4 mmol/mol [−0.4%]) [
22], meta-analyses performed on FM and HbA
1c, mean −4.5 mmol/mol [−0.4%] in uncontrolled studies [
7], and a registry-study from the Netherlands (mean −3.3 mmol/mol [−0.3%]) [
11]. Less than half of the FM users were followed-up for more than 1 year post-initiation, therefore more longitudinal follow-up is needed to establish the long-term persistence of the improvements in HbA
1c.
Only a few studies have looked at FM use and DKA so far. Our findings regarding DKA overall are in keeping with those of other nationwide studies regarding DKA hospitalisation rates [
9,
14]. In a French nationwide database, Roussel et al. [
14] reported that DKA hospitalisation rates fell by 56.2% in the year after vs before FM initiation. This reduction is beneficial in terms of individuals’ wellbeing and reductions in healthcare costs, as DKA is expensive to treat [
23].
Stratified analyses of DKA rates following FM initiation are lacking in the literature. The variations in HbA
1c changes from baseline across starting HbA
1c were in keeping with those reported in previous studies: slight increase among those with optimally controlled baseline HbA
1c [
6,
24]; and substantial decrease among those with high baseline HbA
1c [
6,
7,
10,
13,
22]. We also found that reductions in DKA rates post- vs pre-FM were most marked in those with high baseline HbA
1c. These improvements are extremely promising and likely to translate into a reduction in healthcare costs as those with high HbA
1c levels are most at risk of complications [
25].
We found that FM use was associated with improvements in HbA
1c in all SIMD quintiles, showing that this technology benefits all, including those from more-deprived areas. Tsur et al. [
9] also reported significant improvements in HbA
1c among those with lower socioeconomic status. Although the magnitude of reduction in DKA rates was higher among those from least-deprived areas, there were marked improvements in all SIMD quintiles. Unequal distribution of, or access to, this technology may further widen existing inequalities in healthcare, especially since those from more-deprived areas have historically higher HbA
1c [
26] and thus stand to benefit most from FM.
Existing paediatric studies have had small sample sizes [
7,
8] with heterogeneous findings. For example, Campbell et al. [
27] reported a significant decrease in HbA
1c among children aged 4–17 years, while Messaaoui et al. [
28] reported no change in HbA
1c among their sample of children/young people aged 4–20 years. In our study, HbA
1c reduction appeared to be smaller among the paediatric group, although this was expected considering the well-controlled baseline HbA
1c. Conversely, reduction in DKA rates was substantial in children. Among those with high baseline HbA
1c, marked reductions in HbA
1c were observed in all age groups.
Despite minimal observed reduction in HbA
1c and observed increase in crude DKA rate among adolescents, model results accounting for prior trends suggested improvement in both areas. Longer post-FM follow-up is needed among adolescents to better understand how or whether FM use mitigates the usual deterioration in HbA
1c among this age group. It is also important to consider factors other than blood glucose outcomes when evaluating the benefits of FM in this group, such as quality of life. Indeed, qualitative studies [
29,
30] have suggested such improvements in this demographic. Al Hayek et al. [
31] also found a significant reduction in diabetes distress in a sample of 187 adolescents. However, we do not have access to such data and additional work needs to be done to examine whether FM usage among adolescents could be improved further.
The smaller reductions observed among those with prior pump use was consistent with their lower baseline HbA
1c, and was in keeping with other findings [
9]. Individuals using insulin pumps in Scotland attend a structured education programme prior to pump initiation and receive substantial input from diabetes support services. Therefore, gains in terms of HbA
1c are expected to be marginal in this group. The non-significant decrease in DKA is likely due to significant improvements already occurring following pump initiation [
32]. Improvements in this group are expected in terms of quality of life or hypoglycaemia but we did not possess data to assess this.
DKA and HbA1c improved regardless of completion of a diabetes education programme but individual education levels were not available to assess their influence on outcomes.
Interestingly, disparities in DKA rates between strata before FM initiation generally persisted even after the post-FM reductions. This highlights the need to better understand drivers of elevated DKA rates. Indeed, O’Reilly et al. [
33] showed that factors beyond structured education, use of pump and HbA
1c likely contributed to elevated rates among most-deprived quintiles.
Our findings suggest that FM use is associated with a reduction in SHH among those at risk of this complication. Results on FM usage and hypoglycaemia in the literature vary. The IMPACT study [
4] showed a reduction in hypoglycaemia in those with well-controlled HbA
1c. Observational studies reported a significant decrease in severe hypoglycaemia [
5,
9,
13,
14], while Campbell et al. [
27] found time in hypoglycaemia to be unaffected in their paediatric sample. Differences in results are likely due to a combination of differing hypoglycaemia definitions and cohort characteristics/behaviour. It is nonetheless important to understand whether there is any over-adjustment of insulin dose following readings of FM data.
Strengths and limitations
Our study is one of the largest contemporary real-world-setting studies examining the association of FM initiation with glycaemic outcomes combining data from nationwide electronic health records with extensive subgroup analyses, in particular filling a gap in the literature with regards to FM use and DKA. Using data from all individuals with type 1 diabetes in Scotland, we were able to capture current disparities in usage in the country and had enough power to explore a large number of sociodemographic group-specific outcomes.
For comparison, a recent large-scale UK-based voluntary audit [
10] possessed post-FM follow-up HbA
1c measures for only one-third of the users included (3182 out of 9968), while recent national Swedish and French studies [
13,
14] did not examine variations across sociodemographic groups.
We were limited in our analyses of hypoglycaemia by only being able to analyse hospital admissions, which represent a tiny fraction of hypoglycaemic events [
34]. We did not have access to granular glucose data from the Libre devices; this would have allowed better understanding of glycaemic variability and analysis of hypoglycaemia with more precision. Our study suffers from the usual biases linked to observational studies, such as unmeasured confounding or measurement error. Since this study was observational, observed changes were not attributable to FM use in the clear-cut manner of an RCT. However, timing of changes and crude comparisons to non-users support the findings in relation to FM initiation.
Since the end of our study, newer FM models such as the Libre 2 have become available (since January 2021). Our findings pertaining to marked improvements even with first-generation Libre devices herald positive outcomes with more updated Libre versions.
Due to the criteria of eligibility for FM use, our results might not be generalisable to all those with type 1 diabetes. These criteria are less restrictive than eligibility to insulin pumps, which were also found to be associated with improved glycaemic outcomes among people with type 1 diabetes in Scotland [
32]. It is nonetheless crucial to understand the determinants of good response to FMs to optimise a more widespread roll-out. For example, Riveline et al. [
35], among others, showed that scanning frequency is associated with better glycaemic outcomes; however, we did not have access to such data.
Conclusions
Flash glucose monitoring use in Scotland has been associated with clinically important improvements in HbA1c, especially in individuals with high baseline HbA1c who have the most to gain in reducing the risk of diabetes complications. Historically, reducing rates of DKA has proven to be an extremely difficult task and uptake of effective interventions (such as structured education) has often been relatively low. The striking reduction in DKA across the sociodemographic spectrum following FM use is of major clinical importance. More research is needed to better understand how to increase the uptake of FM use and the drivers and features of its effect in order to tighten the existing socioeconomic gaps. Results will need to be updated when longer-term follow-up is available and to keep pace with newer technologies and systems such as newer Libre models, DIY closed-loop systems or officially licensed hybrid-loop systems.
Acknowledgements
We thank the SDRN Epidemiology Group: J. Chalmers (Diabetes Centre, Victoria Hospital, UK), C. Fischbacher (Information Services Division, NHS National Services Scotland, Edinburgh, UK), B. Kennon (Queen Elizabeth University Hospital, Glasgow, UK), G. Leese (Ninewells, Hospital, Dundee, UK), R. Lindsay (British Heart Foundation Glasgow Cardiovascular Research Centre, University of Glasgow, UK), J. McKnight (Western General Hospital, NHS, UK), J. Petrie (Institute of Cardiovascular & Medical Sciences, University of Glasgow, UK), R. McCrimmon (Division of Molecular and Clinical Medicine, University of Dundee, Dundee, UK), S. Philip (Grampian Diabetes research unit, Diabetes Centre, Aberdeen Royal Infirmary, Aberdeen, UK), D. Mcallister (Institute of Health & Wellbeing, University of Glasgow, Glasgow, UK), E. Pearson (population Health and Genomics, School of Medicine, University of Dundee, Dundee, UK), S. Wild (Usher Institute, University of Edinburgh, Edinburgh, UK) and F. Gibb (Royal Infirmary of Edinburgh, Edinburgh, UK). The SDRN Epidemiology Group resource was originally set up with approval from the Scottish A research ethics committee (ref
11/AL/0225), Caldicott Guardians and the Privacy Advisory Committee (PAC ref.
33/11), now running with approval from the Public Benefit and Privacy Panel for Health and Social Care (PBPP ref. 1617-0147). TMC is a Diabetes UK ‘Sir George Alberti Clinical Research Fellow’ (Grant number: 18/0005786).
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.