Frequently Asked Questions
Where do I find my mean glucose and standard deviation?
CGM apps and receiver software (Dexcom Clarity, LibreView, Tidepool) all report mean glucose and standard deviation in their summary statistics, typically labeled as 'Average Glucose' and 'Standard Deviation' or 'SD.' You need at least 7 to 14 days of data for a representative CV. For finger-stick logs, you can calculate mean and standard deviation manually or using a spreadsheet.
How does CV differ from standard deviation alone?
Standard deviation is an absolute measure (e.g., 40 mg/dL). CV normalizes the standard deviation by the mean, making it a relative measure (e.g., 40 ÷ 150 = 26.7%). A standard deviation of 40 mg/dL means something very different for a person with a mean of 80 mg/dL (CV 50%, dangerously variable) versus a mean of 200 mg/dL (CV 20%, relatively stable). CV is therefore more meaningful for comparing variability across different glucose levels or different people.
Why might my estimated HbA1c differ from my lab HbA1c?
The ADAG formula was derived from a clinical study and has a standard error of about 0.5% HbA1c at the population level. Individual variation can be larger. Factors that cause discordance include unusual red blood cell lifespan (shorter in hemolytic anemia, longer in iron-deficiency anemia), laboratory assay variation, and the fact that a single reading or a short data window may not represent the full 3-month average that HbA1c reflects.
What is a good target CV for someone with diabetes?
The international consensus target is CV below 36% for most adults with diabetes. Lower is generally better; many well-controlled individuals using CGM achieve CV below 25 to 30%. The most important targets to discuss with your healthcare team are your personal time-in-range goal, hypoglycemia avoidance, and HbA1c target, which vary based on age, hypoglycemia risk, and treatment goals. This is general information, not medical advice - consult your doctor for personalized guidance.
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General information only. Not medical advice.
Health & Medical Disclaimer: General information only. Not medical advice.
This calculator provides general health information only and is not medical advice. Results do not replace professional medical evaluation or diagnosis. Consult a licensed healthcare provider before making health decisions. Always seek immediate medical attention for emergencies.