What is the Glucose Management Indicator?
The Glucose Management Indicator is a new metric that represents the average A1c level one would expect based on mean glucose levels over a time period.
The Glucose Management Indicator is calculated by taking the average value of your sugar readings, which is then converted from mg/dL to a percentage using the following formula:
GMI (%) = 3.31 + 0.02392 x [mean glucose in mg/dL]
Or converted from mmol/L to mmol/mol using the following formula:
GMI (mmol/mol) = 12.71 + 4.70587 x [mean glucose in mmol/L]
The GMI is not a substitute for your lab A1c measurement.
The GMI uses a new formula derived from CGM data and NGSP-certified central lab A1C measurements taken from a large number of people with diabetes.
It is only as accurate as your CGM's readings. And many CGMs are calibrated using regular blood glucose monitors, which also have a degree of error (+/- ~15%).
The correlation between GMI and lab A1C may differ between people due to other factors, including recent fluctuations in your readings, red blood cell lifespan, or variations in glucose-hemoglobin binding.
It is important to note that the Sugarmate app's GMI often does not reflect a 90 day average, since:
The Sugarmate app only collects data starting from one day before you signed up for the service. So if you haven't used Sugarmate for at least 90 days, the GMI will reflect a shorter time period.
The GMI tile can be set to display the average over different time ranges (by tapping the tile).
The GMI is best used when it reflects at least 14 days of readings, and will likely be closer to your lab A1c measurement after the Sugarmate app has collected 90 days of readings.
How is GMI different than Estimated A1c?
The GMI was created to replace the Estimated A1c measurement, and the formula used to calculate the GMI is different than the Est. A1c. The two values are correlated, but they are often not identical. The hope is that the GMI's value is a better reflection of an individual's lab A1c.
Hemoglobin A1c Accuracy
Your hemoglobin A1c is a good indicator of your sugar levels for the last 90 days. That said, according to the NIH website, two A1c measurements taken from the same blood sample can be off by as much as 0.4 percent.