What are the current recommendations for continuous glucose monitoring (CGM) use in adults with diabetes, including type 1 diabetes, type 2 diabetes on insulin therapy, pregnant patients, and those with severe hypoglycemia or hypoglycemia unawareness?

Recommendations for Continuous Glucose Monitoring in Diabetes

Type 1 Diabetes: Universal Recommendation

All patients with type 1 diabetes should use continuous glucose monitoring regardless of age or current glycemic control, as this technology consistently reduces hypoglycemia and improves time in range without increasing adverse events. 1, 2

Specific Type 1 Diabetes Populations

• Adults with type 1 diabetes capable of daily CGM use should receive it, particularly when not meeting glycemic targets, experiencing hypoglycemia unawareness, or having recurrent hypoglycemic episodes 3, 1
• Real-time CGM (rtCGM) should be used in conjunction with insulin as a tool to lower HbA1c levels and/or reduce hypoglycemia in teens and adults with type 1 diabetes who are not meeting glycemic targets, have hypoglycemia unawareness, and/or episodes of hypoglycemia (Grade A recommendation - highest quality evidence) 3
• Children and adolescents with type 1 diabetes should be offered CGM whether using multiple daily injections or insulin pumps, with benefits correlating directly with adherence to ongoing device use 1, 2
• Real-time CGM is approved for nonadjunctive use in children aged ≥2 years, and intermittently scanned CGM is approved for children aged ≥4 years 1

Type 1 Diabetes in Pregnancy

• Pregnant women with type 1 diabetes should use real-time CGM to improve HbA1c levels, time in range, and neonatal outcomes (Grade B recommendation - moderate quality evidence) 3, 1

Type 2 Diabetes: Insulin-Treated Patients

Type 2 diabetes patients on intensive insulin therapy (≥3 injections daily or insulin pump) should use CGM to lower A1C and reduce hypoglycemia. 1, 2, 4

Specific Type 2 Diabetes Indications

• Real-time CGM or intermittently scanned CGM should be considered to lower HbA1c and/or reduce hypoglycemia in adults with type 2 diabetes who are using insulin and not meeting glycemic targets (Grade B recommendation - moderate quality evidence) 3
• Multiple RCTs in type 2 diabetes on multiple daily injections, mixed therapies, and basal insulin have consistently shown reductions in A1C levels and increases in time in range (70–180 mg/dL) without reduction in rates of hypoglycemia 3
• The DIAMOND study demonstrated that CGM use in type 2 diabetes patients on multiple daily injections reduced A1C by 0.3 percentage points compared to self-monitoring of blood glucose 4

High-Risk Type 2 Diabetes Situations

CGM is mandatory for type 2 diabetes patients experiencing:

• Unexplainable severe hypoglycemia 1, 2, 4
• Recurrent hypoglycemia 1, 2, 4
• Asymptomatic hypoglycemia or hypoglycemia unawareness 1, 2, 4
• Nocturnal hypoglycemia 1, 2, 4
• Unexplainable hyperglycemia, especially fasting hyperglycemia 1, 2
• Dramatic glycemic variability despite self-monitoring of blood glucose 1, 2
• HbA1c above target despite multidrug oral and/or non-insulin injectable therapies 1, 2

Emerging Type 2 Diabetes Indications

• Recent evidence supports intermittent CGM use in type 2 diabetes patients on noninsulin and/or basal insulin therapies, with a 2024 meta-analysis demonstrating reduced HbA1c and improved treatment satisfaction 4
• Professional CGM used intermittently can help identify and correct patterns of hyper- and hypoglycemia in type 2 diabetes patients not on insulin 4

Special Clinical Situations

Pregnancy and Gestational Diabetes

• Gestational diabetes patients and women with pre-existing diabetes during pregnancy should use CGM as an adjunct to pre- and postprandial blood glucose monitoring to achieve A1C targets and improve neonatal outcomes 1, 2

Hospitalized Patients

• Hospitalized type 2 diabetes patients on insulin therapy in non-ICU settings benefit from real-time CGM to reduce glucose fluctuations and achieve stable glycemic targets without increasing hypoglycemia risk 1, 2
• Perioperative glycemic control in type 2 diabetes patients is improved with real-time CGM 1, 2

Other Medical Conditions

• Diabetes patients with gastroparesis should use CGM 1, 2
• Special types of diabetes with dramatic glycemic variability should use CGM 1, 2
• Endocrine disorders accompanied by dramatic glycemic variability should use CGM 1, 2

Device Selection: Real-Time vs Intermittently Scanned CGM

Real-Time CGM (rtCGM)

• Provides automated alarms and alerts at specific glucose levels and for changing glucose levels 3
• Shows advantages over intermittently scanned CGM for time in range (+5.63%, P<0.001) and hypoglycemia reduction (-1.28%, P<0.001) 5
• Most RCTs in adults with type 1 diabetes show that rtCGM leads to lower HbA1c and reduced time in the hypoglycemic range 3

Intermittently Scanned CGM (isCGM)

• Measures glucose continuously but requires scanning for visualization and storage of glucose values 3
• Must be scanned at minimum once every 8 hours for effectiveness 1, 2
• Consider using intermittently scanned CGM in conjunction with insulin as a tool to lower HbA1c levels and/or reduce hypoglycemia in adults with type 1 diabetes who are not meeting glycemic targets, have hypoglycemia unawareness and/or episodes of hypoglycemia (Grade B recommendation - moderate quality evidence) 3
• One RCT in adults with type 1 diabetes showed less time in the hypoglycemic range without significant change in HbA1c 3

Professional (Blinded) CGM

• CGM devices placed in the health care professional's office and worn for 7–14 days 3
• Data may be blinded or visible to the person wearing the device 3
• Blinded CGM data, when coupled with diabetes self-management education and medication dose adjustment, helps identify and correct patterns of hyper- and hypoglycemia in people with type 1 or type 2 diabetes 3, 1, 4
• Periodic use of real-time, intermittently scanned, or professional CGM can be helpful when continuous use is not appropriate, desired, or available 1, 2, 4

Critical Prerequisites for Success

Robust diabetes education, training, and ongoing support are required for optimal CGM implementation and ongoing use. 1, 2, 4

Patient Requirements

• Patients must be willing and able to learn the basic mechanical skills of the equipment 1, 2, 4
• Users need ability to perform self-monitoring of blood glucose for calibration (device-dependent) and verification of readings when discordant from symptoms 1, 2
• Optimal CGM requires an assessment of individual readiness to use the technology as well as initial and ongoing education and support 1

Usage Frequency for Maximum Benefit

Real-time CGM devices should be used as close to daily as possible for maximal benefit, as the greatest predictor of HbA1c lowering with CGM for all age groups is frequency of sensor use. 1, 2

• Better adherence in wearing the real-time CGM device resulted in a greater likelihood of an improvement in glycemic control 3
• One critical component to success with CGM is near-daily wearing of the device 3
• Benefits of CGM correlate directly with adherence to ongoing device use 1, 2

Absolute Contraindications and Critical Limitations

Where CGM Should NOT Be Used

Intensive care units are not suitable for CGM due to skin edema, vasoconstrictor drugs, hypotension, hypoxemia, and high-dose acetaminophen which adversely affect sensor accuracy 1, 2, 4

Patient-Related Contraindications

• CGM is not suitable for patients unwilling to learn device operation, as success depends on sustained use and proper data interpretation 1, 2

Technical Limitations to Understand

CGM measures interstitial fluid glucose, which lags behind blood glucose by 5-15 minutes during rapid changes. 1, 2

• Accuracy is lowest in hypoglycemic ranges, a critical limitation for patients with problematic hypoglycemia 1, 2, 4
• Verify CGM readings with capillary blood glucose testing during rapid glucose changes or when symptoms are discordant with readings 4

Interference and Safety Concerns

• Skin reactions (irritation or allergy) should be assessed and addressed to aid successful device use 1
• Avoid exposure to strong magnetic fields, MRI, and in some devices conventional X-ray and CT scanning 1
• High-dose acetaminophen (at higher than therapeutic doses) can interfere with glucose meter accuracy 1, 4
• Ascorbic acid (vitamin C) can affect CGM readings 1
• Uraemic toxins in patients with kidney disease may interfere with readings 1
• Certain medications like tetracycline and mannitol (for implantable sensors) can affect accuracy 1

CGM Metrics and Glycemic Targets

Primary Metrics

• Time in range (70–180 mg/dL) is the primary metric for assessing glycemic control 1
• Time below target (<70 and <54 mg/dL) identifies hypoglycemia risk 1
• Time above target (>180 mg/dL) identifies hyperglycemia patterns 1
• CGM metrics derived from the most recent 14 days (or longer for patients with more glycemic variability) should be used in conjunction with A1C whenever possible 1

Evidence of Effectiveness

• CGM significantly reduced HbA1c compared to standard monitoring (mean difference: 0.38%, 95% CI: 0.49 to -0.27%) 5
• Time in range increased by 7.9% (95% CI: 5.8-10.0%), representing 114 additional minutes daily in best range 5
• Benefits were greater among patients with higher baseline HbA1c (>8.5%: 0.68% reduction in HbA1c vs. <7.5%: 0.24% reduction in HbA1c, P = 0.009) 5

Educational and Behavioral Benefits

• CGM facilitates understanding of glucose changes from diet, exercise, alcohol, stress, sleep, and medications, motivating patients to establish healthy lifestyles and improving treatment adherence 1, 2

Common Pitfalls to Avoid

• Do not prescribe CGM without ensuring adequate education and ongoing support, as the willingness and ability of patients to use the CGM system are directly related to efficacy 4
• Do not rely solely on CGM readings during rapid glucose changes—always verify with capillary blood glucose testing when symptoms are discordant with readings 4
• Do not expect benefit without near-daily sensor wear—frequency of use is the strongest predictor of HbA1c reduction across all age groups 1, 2