Understanding CGMs: What Do All Those Glucose Numbers Mean?

When you look at your continuous glucose monitor, you may find so many numbers and abbreviations that they make you dizzy. How do you make sense of it all? Mastering your Continuous Glucose Monitoring (CGM) metrics like CV, SD, and TIR is key to fine-tuning diabetes management. Read on for the optimal targets for stable blood sugar and take control of your health journey today!

Target levels for metrics like coefficient of variation (CV), standard deviation (SD), and time in range (TIR) can vary depending on individualized treatment goals and your specific needs. However, here are some general guidelines:

1. Coefficient of Variation (CV):
   • Definition: CV is a measure of glucose variability, expressed as a percentage. It is calculated as the standard deviation divided by the mean glucose level.
   • Target Level: A lower CV indicates less glucose variability, which is generally desirable. A CV of 36% or lower is often considered a good target for CGM users.
2. Standard Deviation (SD):
   • Definition: SD measures the average deviation or spread of glucose readings from the mean value.
   • Target Level: A lower SD indicates more stable blood glucose levels. While specific targets can vary, an SD below 36 mg/dL (2.0 mmol/L) is often considered favorable.
3. Time in Range (TIR):
   • Definition: TIR represents the percentage of time during which a person's blood glucose levels are within a specified target range.
   • Target Level: The target range for TIR can vary depending on individualized treatment goals and factors like age, co-morbidities, and specific treatment plans. A common target range is 70-180 mg/dL (3.9-10 mmol/L), but this may be adjusted based on individual circumstances.

So What Do These Numbers Mean For You?

Variability is low but the standard deviation (SD) is high suggests that while the overall trend of blood glucose levels is relatively stable, there are occasional significant spikes or drops in glucose readings.If this sounds like you, your blood glucose levels are generally well-controlled and stay within a narrow range most of the time. However, occasionally, they experience brief periods of very high or very low glucose levels. You likely have a few inconsistencies in your lifestyle where controlling your glucose on special occasions may be difficult.

Variability is high but the standard deviation (SD) is low indicates consistent but frequent fluctuations in blood glucose levels within a narrow range.  In other words, your glucose levels are frequently shifting, possibly due to factors like meals, exercise, or stress. However, these changes are relatively mild and don't result in extreme highs or lows.

What to Do About It?

It's important to consider the context and timing of these fluctuations. Are there specific triggers, such as meals or exercise, that are consistently causing these variations? Understanding the patterns can help in tailoring a diabetes management plan to better control blood glucose levels.

Remember that these are general guidelines, for targets perfect for your own lifestyle and needs, always talk with a healthcare provider. The specific targets may be adjusted based on factors like age, overall health, presence of co-morbidities, and your symptoms and preferences.