In January 2020, the American Diabetes Association (ADA) released its annual Standards of Medical Care in Diabetes, outlining current clinical practice recommendations, including a report showing that continuous glucose monitoring (CGM) technology greatly expands the ability to assess glycemic control throughout the day. This technology offers critical data that can quantify time below, within, and above established glucose targets and inform daily treatment decisions.
Out With the Old
Despite being a well-established, population-health marker of the risk of developing long-term diabetes complications, A1C has at least three limitations as the primary glucose management metric:
- Using A1C to guide management decisions has not helped patients achieve desired national glycemic control goals.
- The A1C test is not reliable in up to 20% of patients, including those with a hemoglobinopathy, iron deficiency, significant renal or liver disease, hemolytic anemias, or a prolonged or short red blood cell lifespan. Some medications impact the A1C measure too.
- Most importantly, A1C is a measure of average glucose and cannot guide therapy changes based on potentially dangerous hypoglycemia or disruptive glucose variability.
In With the New
In recent years, CGM systems have become quite small and accurate and are typically covered by most insurance companies for patients on insulin. The latest real-time CGM systems read glucose values and their rate of change every 5 minutes, sending that data to a patient’s dedicated reader or smart device, and thus, allowing patients to learn how foods and physical activity affect their glucose values. Low glucose alerts are also built into CGM systems to warn users in advance of a hypoglycemic event, allowing them time to take appropriate action.
Over the past several years, the diabetes community has had differing views on the most valuable metrics offered by this new technology. However, in the past year, clinicians, researchers, and stakeholder groups agreed on 10 core metrics to guide diabetes clinical care. The first five are:
- Number of days CGM device is worn (recommend 14 days).
- Percentage of time CGM device is active (recommend 70% of data from 14 days).
- Mean glucose – for comparison to last value.
- Glucose management indicator (GMI) – formerly called estimated A1C.
- Glycemic variability target less than or equal to 36%.
The remaining five metrics focus on the amount of time patients are below, in, and above the desired glucose targets. They are:
- Time in range of 70-180 mg/dL should be greater than 70% of the day (16 hours, 48 minutes).
- Time below 70 mg/dL should be less than 4% of the day (58 minutes).
- Time below 54 mg/dL should be less than 1% of the day (14 minutes).
- Time above 180 mg/dL should be less than 25% of the day (6 hours).
- Time above 250 mg/dL should be less than 5% of the day (1 hour, 12 minutes).
Note: Each 5% increase in a patient’s time in range of 70-180 mg/dL is clinically beneficial.
With the establishment of these time-in-range goals, clinicians can now use the ADA-endorsed Ambulatory Glucose Profile (AGP) to tailor therapy to each patient. The AGP is a one-page summary of the time-in-range goals and shows how blood sugar levels change throughout the day.
While A1C has been the standard measure of glycemic control for people with diabetes for nearly 30 years, times are changing. CGM is a good example of how advances in technology can provide actionable metrics like time in range and AGP to guide a safe and effective diabetes management plan.
Understanding Continuous Glucose Monitoring data
The A1C Test & Diabetes