The first RCT, performed by Deiss and colleagues, investigated a needle-type continuous subcutaneous glucose monitor in patients with poorly controlled type 1 diabetes (HbA
1c ≥ 8.1% on intensive treatment) [
9]. There was a difference in HbA
1c reduction of 0.6% after 3 months in favour of patients who were instructed to use the device continuously, as compared with patients using conventional treatment. In a third arm, patients used CGM biweekly, and this did not result in a significant HbA
1c improvement. A subsequent 26 week randomised treat-to-target study performed by Hirsch and coworkers (the STAR 1 trial) yielded disappointing results [
10]. There was no significant difference in change in HbA
1c between type 1 diabetes patients using CSII randomised to either augmenting their current therapy with CGM or continuing with their standard self-monitoring of blood glucose (SMBG). In both groups, there was a decrease in HbA
1c of 0.6–0.7%. That the decreases in HbA
1c were comparable in both groups was attributed to intensification of the treatment in both the control and intervention groups. It seems that in an attempt to assure equal attention times in both groups, the control group was treated more intensively than would be feasible in daily practice. In the Juvenile Diabetes Research Foundation (JDRF) study, three different age groups (≥25, 15–24 and 8–14 years) were randomised to either CGM or SMBG continuation [
11]. All patients had type 1 diabetes and the vast majority were already using CSII. The mean difference in HbA
1c change was 0.5% after 26 weeks in favour of patients using CGM, but this was only in those aged 25 years and older. No significant difference in HbA
1c change was detected in the other age groups. In both the STAR 1 and the JDRF trials, the frequency of sensor usage was strongly correlated to the decrease in HbA
1c. This is in line with the study from Deiss et al. [
9] and the recently published RealTrend study [
12]. In this latter study, patients administering multiple daily injections and with an HbA
1c ≥ 8% at inclusion started with either CSII therapy or sensor-augmented pump therapy for 26 weeks. From a predefined analysis, HbA
1c improved compared with the CSII group only in patients using the sensor >70% of the time. Unfortunately, patients in the sensor-augmented pump group had already used CGM for 9 days before the baseline HbA
1c measurement was performed and therefore the observed HbA
1c difference, 0.41%, may have been underestimated. The combination of CGM and CSII has also been investigated in the recently presented Eurythmics trial, where a difference in HbA
1c improvement of 1.21% in favour of the sensor-augmented pump group was found when type 1 diabetes patients (HbA
1c at entry ≥8.2%), who were using multiple daily injection therapy and SMBG, were randomised to continuing their current therapy or starting CGM-augmented insulin-pump therapy [
13]. It is interesting that the JDRF trial and the Eurythmics trial, both showing a significant HbA
1c improvement in the intervention group, confronted patients with a short period of blinded CGM usage at baseline before randomisation. Patients who did not tolerate the device, and therefore would be likely to drop out or be non-compliant during the study course, were at least partly filtered out before randomisation.