What is the recommended method for monitoring glucose levels in individuals with diabetes, particularly those using insulin therapy?

Continuous Glucose Monitoring for Diabetes Management

Primary Recommendation

Continuous glucose monitoring (CGM) should be the standard glucose monitoring method for all patients with type 1 diabetes and for patients with type 2 diabetes on intensive insulin therapy (multiple daily injections or insulin pump), as it provides superior glycemic control and hypoglycemia prevention compared to self-monitoring of blood glucose (SMBG) alone. 1

Who Should Use CGM

Strong Indications (Use CGM as Standard of Care)

Type 1 Diabetes:

• All children and adolescents with type 1 diabetes should use CGM regardless of their current A1C level or insulin delivery method (injections or pump). 1
• All adults with type 1 diabetes on intensive insulin regimens should use real-time CGM, particularly when not meeting glycemic targets, experiencing hypoglycemia unawareness, or having frequent hypoglycemic episodes. 1
• CGM use in type 1 diabetes reduces A1C by approximately 0.30% when used properly in conjunction with insulin therapy. 1

Type 2 Diabetes on Intensive Insulin:

• Patients with type 2 diabetes using multiple daily insulin injections or insulin pump therapy should use CGM, especially when experiencing unexplainable severe or recurrent hypoglycemia, asymptomatic hypoglycemia, nocturnal hypoglycemia, or dramatic glycemic variability. 1
• Real-time and intermittently scanned CGM are both effective tools to lower A1C and reduce hypoglycemia in insulin-treated type 2 diabetes. 1

Pregnancy:

• Real-time CGM should be used in pregnant women with type 1 diabetes to improve A1C levels, time in range, and neonatal outcomes. 1
• Gestational diabetes patients and women with diabetes during pregnancy benefit from CGM for understanding glucose patterns. 1

Moderate Indications (Consider CGM)

Type 2 Diabetes on Basal Insulin:

• Patients with type 2 diabetes whose A1C remains above target despite multidrug oral and/or non-insulin injectable therapies may benefit from CGM. 1
• CGM prevents glycemic deterioration even in well-controlled insulin-treated type 2 diabetes patients (A1C <8%), with a net benefit of -0.30% A1C reduction. 2

Special Populations:

• Patients with gastroparesis, special types of diabetes, or endocrine disorders with dramatic glycemic variability. 1
• Patients with advanced chronic kidney disease or end-stage kidney disease on dialysis, where HbA1c measurements are unreliable due to altered erythrocyte lifespan. 1

CGM vs. SMBG: When to Use Each

Use CGM Instead of SMBG When:

• Patient is on intensive insulin therapy (≥3 injections daily or pump). 1
• Patient has hypoglycemia unawareness or frequent hypoglycemic episodes. 1
• Patient has unexplainable glycemic variability despite SMBG-guided therapy. 1
• Patient is pregnant with type 1 diabetes. 1

Continue SMBG When:

• Patient is on basal insulin only with stable glycemic control. 1
• Patient has type 2 diabetes managed with oral agents alone (routine monitoring shows limited benefit). 1
• CGM calibration is required (some systems still need periodic SMBG for calibration). 1
• CGM readings are discordant with symptoms (SMBG verification needed). 1

Critical Implementation Requirements

For Optimal CGM Effectiveness:

Usage Frequency:

• Real-time CGM devices must be used as close to daily as possible for maximal benefit. 1
• Intermittently scanned CGM devices (like FreeStyle Libre) must be scanned at minimum once every 8 hours. 1
• Benefits of CGM correlate directly with adherence to ongoing device use. 1

Education and Training:

• Robust diabetes education, training, and support are mandatory for optimal CGM implementation and ongoing use. 1
• Patients must maintain ability to perform SMBG for calibration and/or verification of readings when discordant from symptoms. 1
• Assess individual readiness for continuing CGM use before prescribing, given variable adherence patterns. 1

Data Utilization:

• Record diet, exercise, medication, and other events during CGM monitoring to interpret patterns effectively. 1
• Use CGM metrics including time in range (TIR >70%), time below range (TBR <1%), and glucose management indicator (GMI) for treatment decisions. 1
• Blinded CGM data, when coupled with diabetes self-management education and medication dose adjustment, helps identify and correct patterns of hyper- and hypoglycemia. 1

SMBG Frequency When CGM Not Available

For Intensive Insulin Users:

• Test at minimum 6-10 times daily: before each meal and snack, at bedtime, occasionally postprandially, prior to exercise, when suspecting hypoglycemia, after treating hypoglycemia until normoglycemic, and before critical tasks like driving. 1, 3

For Basal Insulin Users:

• Test fasting glucose daily to inform basal insulin dose adjustments. 1
• Occasional postprandial checks help assess meal coverage. 4

For Type 2 Diabetes on Oral Agents Only:

• Routine SMBG is not recommended as it shows limited clinical benefit without a treatment adjustment program. 1
• Consider targeted testing when altering diet, physical activity, or medications, particularly those causing hypoglycemia. 1

Common Pitfalls and How to Avoid Them

CGM Accuracy Issues:

• CGM is not approved for use in critically ill patients, those on peritoneal dialysis with icodextrin, or in conditions causing skin edema or requiring vasoconstrictors (affects interstitial fluid glucose accuracy). 1
• Patients with advanced CKD should use CGM-derived metrics (mean glucose, TIR) rather than HbA1c due to measurement bias from altered erythrocyte lifespan. 1

SMBG Accuracy Issues:

• Only use FDA-approved meters with unexpired strips from licensed distributors. 1
• Be aware of interfering substances: glucose oxidase monitors are affected by uric acid, galactose, xylose, acetaminophen, L-dopa, and ascorbic acid; glucose dehydrogenase monitors are affected by icodextrin. 1
• Glucose oxidase monitors are oxygen-sensitive: arterial blood or oxygen therapy causes falsely low readings; hypoxia or venous blood causes falsely high readings. 1

Underutilization:

• CGM technology is underprescribed despite proven benefits in reducing complications and improving quality of life. 5
• Ensure continued CGM access for patients who turn 65 years of age, as benefits persist across age groups. 1

Inadequate Follow-up:

• Ongoing instruction and regular evaluation of monitoring technique, results interpretation, and ability to use data for therapy adjustment is essential. 1
• Reevaluate the need for and frequency of monitoring at each routine visit to avoid overuse when not effectively used for self-management. 1