Evidence-Based Indications for Continuous Glucose Monitoring in Type 2 Diabetes
Real-time and intermittently scanned continuous glucose monitors are useful tools to lower A1C and/or reduce hypoglycemia in adults with type 2 diabetes who are not meeting glycemic targets, particularly those on intensive insulin therapy (≥3 injections daily or insulin pump). 1
Primary Indications for Type 2 Diabetes
Intensive Insulin Therapy
Type 2 diabetes patients on intensive insulin regimens (multiple daily injections or continuous subcutaneous insulin infusion) should use CGM to lower A1C levels and reduce hypoglycemia. 1, 2, 3 This represents a Grade B recommendation from the American Diabetes Association, indicating strong evidence from randomized controlled trials. 1
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. 1, 4
Problematic Hypoglycemia
CGM is indicated for type 2 diabetes patients experiencing unexplainable severe hypoglycemia, recurrent hypoglycemia, asymptomatic hypoglycemia (hypoglycemia unawareness), or nocturnal hypoglycemia. 2, 3 This is particularly critical because these patients have lost autonomic warning symptoms that normally precede neuroglycopenia, increasing their risk of severe episodes. 1
Real-time CGM serves as a detection tool for asymptomatic hypoglycemia, allowing patients to avoid severe hypoglycemic episodes that could be life-threatening. 1, 5, 6
Inadequate Glycemic Control
Type 2 diabetes patients not meeting glycemic targets despite intensive therapy should use CGM. 1 This includes patients with HbA1c above target despite multidrug oral and/or non-insulin injectable therapies. 2, 3
CGM provides continuous data every 5 minutes, capturing glucose fluctuations that intermittent fingerstick testing misses, which is essential for identifying patterns of hyperglycemia and hypoglycemia. 7
Significant Glucose Variability
Patients with dramatic glycemic variability despite self-monitoring of blood glucose require CGM. 2, 3 This includes those with unexplainable hyperglycemia, especially fasting hyperglycemia. 2, 3
CGM helps identify and correct patterns of hyper- and hypoglycemia when coupled with diabetes self-management education and medication dose adjustment. 1, 2
Emerging Indications in Type 2 Diabetes
Non-Insulin Treated Patients
Recent evidence supports intermittent CGM use in type 2 diabetes patients on noninsulin and/or basal insulin therapies. 1 A 2024 meta-analysis of six randomized controlled trials demonstrated that CGM in noninsulin-treated type 2 diabetes patients reduced HbA1c by 0.31%, increased time in range by 8.63%, and improved treatment satisfaction compared to self-monitoring. 8
Professional CGM used intermittently at baseline and 6 months in type 2 diabetes patients not on insulin resulted in lower A1C and a shift toward medications with cardiometabolic benefits (SGLT2 inhibitors and GLP-1 receptor agonists). 1
Special Clinical Situations
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. 2, 3
Perioperative glycemic control in type 2 diabetes patients is improved with real-time CGM. 2, 3
Type 2 diabetes patients with gastroparesis or special types of diabetes with dramatic glycemic variability should use CGM. 2
Critical Prerequisites for Successful CGM Use
Education and Training Requirements
Robust diabetes education, training, and ongoing support are required for optimal CGM implementation and ongoing use. 1, 2, 3 This is a Grade E recommendation (expert consensus) from the American Diabetes Association, emphasizing that CGM success depends on proper patient preparation. 1
Patients must be willing and able to learn the basic mechanical skills of the equipment, as optimal CGM requires sustained use and proper data interpretation. 1, 2, 3
Blood Glucose Monitoring Capability
CGM users need the ability to perform self-monitoring of blood glucose to calibrate their monitor (for devices requiring calibration) and verify readings when discordant from symptoms. 1, 2, 3 This is essential because CGM measures interstitial fluid glucose, which lags behind blood glucose by 5-15 minutes during rapid changes. 2, 3
Capillary blood glucose testing should be performed when CGM suggests hypoglycemia, when a patient suspects hypoglycemia, or when there is discordance between symptoms and sensor readings. 1
Usage Frequency
Real-time CGM devices should be used as close to daily as possible for maximal benefit, as the greatest predictor of HbA1c lowering is frequency of sensor use. 1, 3 Intermittently scanned CGM devices must be scanned at minimum once every 8 hours. 1, 3
Benefits of CGM correlate directly with adherence to ongoing device use. 1, 2, 3
Important Contraindications and Limitations
Clinical Settings 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. 2, 3 This is a critical safety consideration that must be respected.
Technical Limitations
CGM accuracy is lowest in hypoglycemic ranges, which is a critical limitation for patients with problematic hypoglycemia. 2, 3 This paradox means that the patients who most need accurate readings during hypoglycemia are receiving the least accurate data.
Sensor interference occurs with several medications and substances, including hydroxyurea (causes falsely elevated readings), high-dose acetaminophen, mannitol, sorbitol when administered intravenously, and ascorbic acid. 1, 3
Patient Selection Considerations
CGM is not suitable for patients unwilling to learn device operation, as success depends on sustained use and proper data interpretation. 2, 3 This represents a practical barrier that must be assessed before prescribing.
Contact dermatitis (both irritant and allergic) has been reported with all devices that attach to the skin, sometimes linked to isobornyl acrylate. 1 Periodic assessment of adhesive reactions is important to ensure comfortable use and promote self-care. 1
Alternative CGM Use Patterns
Professional and Intermittent CGM
Blinded CGM data (professional CGM), when coupled with diabetes self-management education and medication dose adjustment, helps identify and correct patterns of hyper- and hypoglycemia in type 2 diabetes. 1, 2, 3 This is a Grade E recommendation from the American Diabetes Association. 1
Professional CGM can be particularly useful in individuals using agents that can cause hypoglycemia, as the data can be used to evaluate periods of hypoglycemia and make medication dose adjustments. 1
Periodic use of real-time, intermittently scanned, or professional CGM can be helpful when continuous use is not appropriate, desired, or available. 2, 3 This provides flexibility for patients who cannot commit to continuous CGM use.
Common Pitfalls to Avoid
Do not prescribe CGM without ensuring adequate education and ongoing support. 1 The willingness and ability of patients to use the CGM system are directly related to efficacy. 1
Do not rely solely on CGM readings during rapid glucose changes or when symptoms are discordant with readings. 1, 2, 3 Always verify with capillary blood glucose testing in these situations.
Do not use CGM in type 2 diabetes patients treated with diet and/or oral agents alone as routine practice without specific indications. 1 Four meta-analyses showed that routine blood glucose monitoring in non-insulin-treated type 2 diabetes adds cost without significant benefit. 1 However, the newer evidence for intermittent CGM use in this population shows promise and may change this recommendation. 1, 8
Avoid exposure to strong magnetic fields, MRI, and in some devices conventional X-ray and CT scanning. 2, 3 This can damage the sensor or cause inaccurate readings.