What is the most accurate measure of diabetes control?

Most Accurate Measure of Diabetes Control

HbA1c remains the gold standard for assessing long-term glycemic control in diabetes, but a comprehensive assessment should include continuous glucose monitoring (CGM) metrics, particularly time in range, to provide a complete picture of glycemic control.

HbA1c as the Primary Metric

• HbA1c reflects average glycemia over approximately 3 months and has strong predictive value for diabetes complications 1
• It should be tested at least twice per year in patients meeting treatment goals with stable glycemic control, and quarterly in those whose therapy has changed or who are not meeting glycemic goals 1
• HbA1c is the metric used in clinical trials demonstrating the benefits of improved glycemic control 1
• Point-of-care testing for HbA1c allows more timely treatment changes 1

Limitations of HbA1c

• HbA1c does not measure glycemic variability or hypoglycemia 1
• It may not accurately measure average glycemia in persons with increased turnover of red blood cells 1
• HbA1c is an indirect measure of glycemia and may not correlate with a patient's measured glucose levels in certain conditions 1
• Other measures of average glycemia, such as fructosamine and 1,5-anhydroglucitol levels, might be helpful when HbA1c is unreliable, but their prognostic significance is not as clear 1, 2

Continuous Glucose Monitoring (CGM)

• CGM measures interstitial glucose (which correlates with plasma glucose) and provides more detailed information about glycemic patterns 1
• CGM metrics, particularly time in range (TIR), provide a more personalized approach to diabetes management 3
• The greatest predictor of HbA1c lowering with CGM for all age groups is frequency of sensor use 1
• In type 1 diabetes, glycemic control is best evaluated using the results of CGM, SMBG, and HbA1c testing together 1

Time in Range (TIR)

• TIR has emerged as a key metric that provides information about the quality of glycemic control beyond what HbA1c can offer 3
• It captures both hyperglycemic and hypoglycemic excursions that HbA1c cannot detect 3, 4
• TIR correlates with the risk of developing diabetes-related complications 3

Glucose Management Indicator (GMI)

• GMI calculates an approximate HbA1c level based on the average CGM-driven glucose level 3
• It facilitates individual decision-making when the laboratory-measured HbA1c and estimated HbA1c are discordant 3

Self-Monitoring of Blood Glucose (SMBG)

• SMBG provides point-in-time measurements that help with day-to-day management 1
• In patients with type 1 diabetes, increased daily frequency of SMBG was significantly associated with lower HbA1c levels and fewer acute complications 1
• For patients using intensive insulin regimens, SMBG is essential to adjust therapy and minimize hypoglycemia 1

Practical Approach to Glycemic Assessment

1. Use HbA1c as the foundation: Measure HbA1c every 3-6 months depending on stability of glycemic control 1
2. Incorporate CGM when available: Especially for patients on intensive insulin therapy or with problematic hypoglycemia 1
3. Evaluate time in range: Aim for >70% time in range (70-180 mg/dL) for most patients 3
4. Assess glycemic variability: High variability increases hypoglycemia risk 3, 4
5. Consider limitations: In conditions affecting red blood cell turnover, rely more on CGM or alternative markers 1, 2

Special Considerations

• For patients with frequent hypoglycemia or hypoglycemia unawareness, CGM provides critical information that HbA1c cannot 1
• In pregnancy, more frequent monitoring and tighter targets are required 1
• For elderly patients or those with comorbidities, less stringent HbA1c goals (such as <8%) may be appropriate, with focus on avoiding hypoglycemia 1

Common Pitfalls to Avoid

• Relying solely on HbA1c without considering glycemic variability or hypoglycemia risk 1, 3
• Failing to calibrate glucose meters regularly, which can lead to inaccurate SMBG results 1
• Not accounting for conditions that may affect HbA1c accuracy (hemoglobinopathies, anemia, etc.) 1
• Overlooking the importance of postprandial glucose excursions, which contribute significantly to overall glycemic control 2