Impact Study

The first randomised controlled trial to assess the efficacy and safety
of the FreeStyle Libre system for glucose monitoring in adults with
well-controlled type 1 diabetes.

Evaluating the efficacy of the FreeStyle Libre system in patients with type 1 diabetes

IMPACT was the first randomised controlled trial (RCT) to assess the efficacy and safety of the FreeStyle Libre system vs. self-monitoring of blood glucose (SMBG) for glucose monitoring in adults with well-controlled type 1 diabetes.¹

Published in The Lancet, the IMPACT study was a multicentre, prospective, non-masked RCT by Bolinder et al.

Study objective

Assess whether the FreeStyle Libre system reduced exposure to hypoglycaemia in patients with type 1 diabetes, compared to SMBG.

Study design & study population

IMPACT was a multicentre, prospective, non-masked, RCT that enrolled 328 adult patients with well-controlled type 1 diabetes (HbA1c ≤58 mmol/mol [7.5%]) from 23 European diabetes centres.  

After two weeks of wearing a masked FreeStyle Libre device, participants who had readings for at least 50% of the period were randomly assigned (1:1) to either the FreeStyle Libre glucose monitoring arm (intervention group) or to the SMBG arm (control group) for six months. The primary endpoint was time spent in hypoglycaemia (<3.9 mmol/L) for the 14 days preceding the end of the six-month study period.

Key Inclusion criteria^*

Aged 18 years or over
Diagnosed with type 1 diabetes for ≥ 5 years
On their current insulin regimen for  ≥ 3 months prior to entering the study
Screened HbA1c result ≤ 7.5% (58 mmol/mol)
Reported self-testing of blood glucose levels on a regular basis (a minimum of 3 times daily for at least two months prior to study entry)
Participants needed to be considered technically capable of using the FreeStyle Libre system by the investigator

Key Exclusion criteria^*

Diagnosis with hypoglycaemic unawareness
Diabetic ketoacidosis or acute myocardial infarction in the previous six months
Use of the FreeStyle Libre system or a continuous glucose monitoring (CGM) device within the previous four months
Use of sensor augmented pump therapy
Pregnancy or planned pregnancy

Primary outcome

Time spent in hypoglycaemia (<3.9 mmol/L) during the 14 days preceding the end of the six-month study period

Key secondary outcomes

HbA1c concentrations at six months
Sensor-derived measures for the 14 days preceding the end of the six-month study period, including:
- Number and duration of hypoglycaemic episodes† (sensor glucose <3.9 mmol/L, <3.1 mmol/L, <2.2 mmol/L)
- Time with glucose in range 3.9–10 mmol/L
- Number and duration of hyperglycaemic episodes (>10 mmol/L and 13.3 mmol/L [respectively])
- Glucose variability measurements
Frequency of finger-sticks and sensor scans per day during the study period
Patient-recorded outcome measures

Study results

Key patient baseline characteristics^1,*

The study evaluated outcomes of 239 randomised participants with well-controlled type 1 diabetes (baseline HbA1c 6.7% [50.2 mmol/mol]); 129 participants were randomly assigned to the intervention arm using FreeStyle Libre and 129 to the control arm using SMBG (Table 1).

Table 1 - Baseline and clinical characteristics of participants with type 1 diabetes assigned randomly to the intervention or control group

IQR, interquartile range; SC, subcutaneous; SD, standard deviation; SMBG, self-monitored blood glucose.

Primary & secondary outcomes^*

Difference in hypoglycaemia

Time spent in hypoglycaemia <3.9 mmol/L was significantly reduced in the FreeStyle Libre intervention group (3.38 h/day at baseline to 2.03 h/day at six months [baseline adjusted mean change -1.39]) compared with the SMBG control group (3.44 h/day at baseline to 3.27 h/day at six months [baseline adjusted mean change -0.14]).
The adjusted between-group difference of -1.24 (p<0.0001) equated to a 38% reduction in time in hypoglycaemia in the FreeStyle Libre intervention group compared with the SMBG control group. Notably, reduction of time in hypoglycaemia occurred almost immediately after start of sensor use.
The FreeStyle Libre intervention group also showed significant reductions in time spent in nocturnal hypoglycaemia <3.9 mmol/L and hypoglycaemia <3.1 mmol/L by -40% and -50%, respectively, compared with the SMBG control group.

Figure 1 – Changes in HbA1c and in time with hypoglycaemia (hours per day)

Glucose monitoring

The mean number of self-monitored blood glucose tests performed per day by the FreeStyle Libre intervention group reduced from 5.4 tests per day at baseline to 0.5 tests per day during the study period.

Figure 2 – Glucose monitoring frequency over time

BGM, blood glucose monitoring

Treatment satisfaction

Results of a Diabetes Treatment Satisfaction Questionnaire showed significantly higher total treatment satisfaction with their glucose monitoring method in the FreeStyle Libre intervention group and lower perceived frequency of hypo- and hyperglycaemia than the the SMBG control group.

Figure 3 – Scores from Diabetes Treatment Satisfaction Questionnaire

Safety

No device-related serious adverse events (AE) or safety issues were reported.

Study limitations

Only adults with well-controlled type 1 diabetes (HbA1c <7.5%) were enrolled.
By nature of the study, the intervention was not masked as all participants experienced periods of sensor wear during the study.

Summary

IMPACT was the first RCT to demonstrate the FreeStyle Libre system was effective and safe for reducing exposure to hypoglycaemia in adults with well-controlled type 1 diabetes compared with SMBG.¹

The FreeStyle Libre intervention group showed a significant reduction in time and incidence of hypoglycaemia compared with the SMBG control group, without deterioration in HbA1c levels.

The FreeStyle Libre system showed improved treatment satisfaction and self-management in adults with type 1 diabetes.

Overall, the study results demonstrate that the FreeStyle Libre system is effective and a safe replacement for SMBG to reduce exposure to hypoglycaemia and is highly acceptable for individuals with type 1 diabetes.

References & Disclaimers

Images are for illustrative purposes only. Not real patient data. Study data collected with the FreeStyle Libre system and is applicable to the FreeStyle Libre 2 & FreeStyle Libre 3 systems based on technological similarities.

* A full list of inclusion criteria, exclusion criteria, and primary and secondary outcomes can be found at https://clinicaltrials.gov/study/NCT02232698.

† Episode defined as at least two consecutive readings at 15 min intervals, outside the predefined glucose range. The end of an episode was one reading at or higher than the threshold.

1 Bolinder J, et al. Novel glucose-sensing technology and hypoglycaemia in type 1 diabetes: a multicentre, non-masked, randomised controlled trial. Lancet. 2016;388(10057):2254-2263. doi: 10.1016/S0140-6736(16)31535-5.

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Impact Study

The first randomised controlled trial to assess the efficacy and safety
of the FreeStyle Libre system for glucose monitoring in adults with
well-controlled type 1 diabetes.