Clinical Inquiries

Does use of continuous or flash glucose monitors decrease hypoglycemia episodes in T2D?

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NO. In adults with insulin-treated type 2 diabetes (T2D), continuous glucose monitoring (CGM) and flash glucose monitoring (FGM) do not decrease symptomatic hypoglycemia episodes (strength of recommendation [SOR], B) but do lower time in hypoglycemia (SOR, C; disease-oriented evidence).

CGM, in which glucose levels are sent automatically in numeric and graphic format to a patient’s smart device for their potential action, did not change the hypoglycemic event rate (SOR, B; 2 prospective studies). CGM significantly reduced hypoglycemia duration in an 8-month randomized controlled trial (RCT; SOR, C) but not in a 1-year prospective study (SOR, C).

FGM, in which glucose levels are sent on demand to a device, did not significantly reduce hypoglycemic episodes (SOR, B; 1 small RCT and 1 prospective study). Hypoglycemia duration was reduced significantly with FGM in a 6-month RCT (SOR, B) but not in a 1-year prospective study (SOR, B).



Evidence summary

Continuous glucose monitoring: Nonsignificant reductions in event rates

A 2021 multicenter RCT (N = 175) evaluated CGM effectiveness in patients with basal ­insulin–treated T2D.1 Patients (mean age, 57 years; mean A1C, 9.1%) wore a blinded CGM device for baseline glucose measurement (minimum of 168 hours) before being randomly assigned to either CGM (n = 116) or traditional blood glucose monitoring (BGM; n = 59). At 8-month follow-up, patients in the BGM group again had blinded sensors placed. A significant reduction in hypoglycemia duration was observed for the CGM group vs the BGM group at 8 months for glucose values < 70 mg/mL (adjusted mean difference [aMD] = –0.24%; 95% CI, –0.42 to –0.05) and < 54 mg/dL (aMD = –0.10%; 95% CI, –0.15 to –0.04). A nonsignificant decrease in severe hypoglycemic events requiring resuscitative assistance occurred for BGM (2%) vs CGM (1%) patients. Study limitations included virtual visits due to COVID-19 and a short follow-­up period.

A 2022 multicenter prospective study (N = 174) examined CGM effects on hypoglycemia frequency and severity in adults with T2D.2 Patients with insulin-requiring T2D (mean age, 61 years; mean A1C, 8.0%) participated in a 12-month study with 6 months of self-monitored blood glucose (SMBG) followed by 6 months of CGM use. The primary outcome was the rate of severe hypoglycemic events. A nonsignificant decrease was observed in the CGM group compared to the SMBG group for hypoglycemic event rate, per participant per 6-month period (relative risk [RR] = 0.43; 95% CI, 0.07-2.64). Four moderate hypoglycemic adverse events occurred in the SMBG phase vs 2 in the CGM phase. Financial support by the study sponsor decreases the study’s validity.

A 2021 prospective study (N = 90) evaluated the use of CGM to improve glycemic control.3 Patients younger than 66 years with insulin-treated T2D and an A1C > 7.5% participated in a 7-day blinded CGM cycle every 4 months for 1 year. A nonsignificant decrease in hypoglycemia duration was observed for glucose values < 70 mg/dL and < 54 mg/dL at 12 months. No change in hypoglycemic event rate was seen with the use of CGM. Funding by the device manufacturer was a limitation of this study.

Flash glucose monitoring: Mixed results on hypoglycemia events

A 2019 open-label RCT (N = 82) assessed the effectiveness of FGM on diabetes control.4 Patients with insulin-treated T2D were randomly assigned to the intervention or standard­-care groups. The intervention group (n = 46; mean age, 66 years; mean A1C, 8.3%) used the FGM system for 10 weeks, while the standard-care group (n = 36; mean age, 70 years; mean A1C, 8.9%) maintained use of their glucometers. Both groups received similar types and duration of counseling. Treatment satisfaction was the primary outcome; total hypoglycemic events was a secondary outcome. No significant difference in the number of hypoglycemic episodes was observed between the intervention and control groups at 55 to 70 mg/dL (RR = 0.79; 95% CI, 0.44-1.4) or < 54 mg/dL (RR = 1.27; 95% CI, 0.38-4.2). No adverse events of severe hypoglycemia occurred during the study. Funding by the device manufacturer was a limitation of this study.

Continuous glucose monitoring and flash glucose monitoring do not decrease symptomatic hypoglycemia episodes but do lower time in hypoglycemia.

A 2017 open-label, multicenter RCT (N = 224) assessed FGM efficacy.5 Adults (mean age, 59 years; mean A1C, 8.8%) with T2D on intensive insulin therapy were randomized to FGM (n = 149) or SMBG (n = 75) after a 14-day masked baseline period. The 6-month treatment phase was unblinded. The duration of hypoglycemic events (glucose values < 70 mg/dL and < 55 mg/dL) was obtained from the sensors. Compared to the SMBG group, the FGM group spent 43% less time at < 70 mg/dL (aMD = –0.47 ± 0.13 h/d; P = .0006) and 53% less time at < 55 mg/dL (aMD = –0.22 ± 0.068 h/d; P = .0014). Hypoglycemic event rates significantly decreased by 28% (aMD = –0.16 ± 0.065; P = 0.016) and 44% (aMD = –0.12 ± 0.037; P = .0017) for glucose levels < 70 mg/dL and < 55 mg/dL, respectively. A nonsignificant difference occurred in severe hypoglycemic events requiring third-party assistance for the FGM (2%) vs control (1%) groups. Involvement of the device manufacturer and unblinded group allocations are study limitations.

A 2021 single-arm, multicenter prospective study looked at the impact of FGM on glycemic control in adults with insulin-treated T2D (N = 90; mean age, 64 years; mean A1C, 7.5%).6 After a 14-day baseline period consisting of masked sensor readings paired with self-monitored fingerstick tests, participants were followed for 11 weeks using the sensor to monitor glucose levels. The primary outcome was amount of time spent in hypoglycemia (< 70 mg/dL), with secondary outcomes including time and events in hypoglycemia (< 70, < 55, or < 45 mg/dL). No significant decrease in hypoglycemia duration or hypoglycemic event rates at < 70, < 55, or < 45 mg/­dL was observed for FGM compared to baseline. Adverse events were observed in 64% of participants; 94% of the events were hypoglycemia related. Serious adverse events were reported for 5.3% of participants. The single-arm study format, lack of generalizability due to the single-race study population, and sponsor support were study limitations.

Editor’s takeaway

This reasonably good evidence shows a decrease in measured or monitored hypoglycemia, a disease-oriented outcome, but it did not reach statistical significance for symptomatic hypoglycemia (1% vs 2%), a patient-oriented outcome. Nevertheless, in patients reporting symptomatic hypoglycemia, a continuous or flash glucose monitor may allow for more aggressive glucose control.

Evidence-based answers from the Family Physicians Inquiries Network

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