The Glucose Management Indicator (GMI) provides an estimated HbA1c value derived from continuous glucose monitoring (CGM) data. This metric offers insights into daily glucose patterns, serving as a valuable tool for individuals managing diabetes and their healthcare providers.
What GMI Represents
The Glucose Management Indicator is an estimated A1c percentage. It reflects average glucose readings collected from a continuous glucose monitoring device over a period of 10 to 14 days or more. GMI captures daily glucose patterns and variability, providing a more immediate snapshot of glucose control. For example, a GMI of 6.7% indicates an average glucose level similar to what would result in an HbA1c of 6.7%.
How GMI is Determined
GMI is calculated using a specific formula that converts average glucose readings from CGM data into an estimated A1c percentage. For glucose measured in milligrams per deciliter (mg/dL), the formula is GMI (%) = 3.31 + (0.02392 × mean glucose in mg/dL). Continuous glucose monitoring devices measure glucose levels in the interstitial fluid, the fluid surrounding cells under the skin. This data is then averaged over a recommended period of at least 14 days to generate the GMI value.
Using GMI in Diabetes Care
GMI serves as a practical tool for individuals with diabetes and their healthcare teams to assess immediate glucose control trends. It helps evaluate the effectiveness of recent adjustments to medication, lifestyle changes, or insulin dosing strategies. This metric can identify patterns of high or low glucose levels not apparent from a single laboratory A1c test. GMI offers actionable insights for daily diabetes management, supporting shared decision-making between individuals and their healthcare providers for timely modifications to care plans.
GMI and HbA1c: A Comparison
Hemoglobin A1c (HbA1c) measures average blood glucose levels over the preceding two to three months by assessing glucose attached to hemoglobin in red blood cells. In contrast, GMI is an estimate of HbA1c derived from continuous glucose monitoring data, reflecting glucose trends over a shorter, more recent period of 10 to 14 days. Both metrics play complementary roles in diabetes management: HbA1c offers a long-term view of glucose control, while GMI provides insights into shorter-term trends and glucose variability. While related, GMI and HbA1c are not interchangeable and may differ due to individual biological variations, such as red blood cell lifespan, or the specific timeframes they represent.
Understanding GMI Results
GMI is an estimate and may not always perfectly match a laboratory HbA1c result. Individual physiological differences, such as variations in red blood cell turnover, can influence this discrepancy. The specific continuous glucose monitoring device used and the duration of CGM wear can also impact GMI readings. GMI provides context to glucose patterns, including time in range and glucose variability, which a single HbA1c number does not fully convey. Therefore, GMI should be interpreted with other clinical data and under the guidance of a healthcare professional for a comprehensive understanding of glucose management.