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Glucose Management Indicator (GMI) explained

The glucose management indicator (GMI) estimates the HbA1c value using CGM data. It helps people with diabetes to better understand their long-term blood glucose control.

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The glucose management indicator (GMI) estimates the HbA1c value using CGM data. It helps people with diabetes to better understand their long-term blood glucose control.

What is the Glucose Management Indicator?

The Glucose Management Indicator (abbreviated as GMI) is a metric calculated from continuous glucose monitoring (CGM) data. It estimates the HbA1c value – also known as the long-term blood sugar marker – and thus provides an indication of average glucose control over a defined period. The GMI was developed to give patients and healthcare professionals a more accessible way to assess blood glucose regulation, especially for individuals living with diabetes mellitus.

How is the GMI Calculated?

The GMI is derived from the mean glucose value recorded by a continuous glucose monitoring device over a minimum of 14 days. The formula is as follows:

GMI (%) = 3.31 + 0.02392 × mean glucose value (mg/dL)

The result is expressed as a percentage and is intended to be comparable to a laboratory HbA1c. However, it is important to note that the GMI and the laboratory value are not always identical – individual biological differences can lead to discrepancies.

Difference Between GMI and HbA1c

While the HbA1c is measured in a laboratory from a blood sample and reflects the proportion of glycated haemoglobin (sugar-coated red blood pigment), the GMI is calculated exclusively from CGM readings. Key differences include:

Time frame: HbA1c reflects average blood glucose control over the past 2–3 months, whereas the GMI is typically based on 14 days to 3 months of CGM data.
Accessibility: The GMI can be read directly from CGM software without the need for a blood draw.
Accuracy in special cases: In certain conditions such as haemoglobinopathies or anaemia, laboratory HbA1c values may be distorted; in these situations, the GMI can provide more reliable information.

Clinical Relevance of the GMI

The Glucose Management Indicator is particularly valuable in modern diabetes management. It is often used alongside other key metrics from CGM reports, including:

Time in Range (TIR): The proportion of time blood glucose levels remain within the target range
Time Above Range (TAR): The proportion of time blood glucose is too high
Time Below Range (TBR): The proportion of time blood glucose is too low
Glucose variability: The degree of fluctuation in glucose levels

This combination provides a far more comprehensive picture of glucose regulation than HbA1c alone. International diabetes organisations such as the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD) recommend using the GMI as a complementary parameter in diabetes care.

Target Values and Interpretation

Target GMI values should be individualised and agreed upon with the treating physician. General guidance includes:

GMI below 7%: Good long-term control, the goal for many patients with type 1 or type 2 diabetes
GMI between 7% and 8%: Acceptable range depending on individual circumstances
GMI above 8%: Indicates insufficient blood glucose control; therapy adjustment may be required

Different target values may apply for specific patient groups (e.g., older adults, pregnant women, or children).

Advantages of the GMI Over the Classic HbA1c

The GMI offers several practical advantages:

No additional blood draw required
More frequent and timely assessment of glucose control is possible
Supports therapy adjustments between medical appointments
Greater patient understanding through direct display in CGM apps and devices

Limitations

Despite its benefits, the GMI also has limitations. It requires that the CGM device is worn consistently and correctly. Incomplete data (e.g., sensor failures or short wear periods) can reduce the accuracy of the GMI. Furthermore, it is not a replacement for the laboratory HbA1c, but rather a complement to it.

References

Bergenstal R.M. et al. - Glucose Management Indicator (GMI): A New Term for Estimating A1C From Continuous Glucose Monitoring. Diabetes Care, 2018. DOI: 10.2337/dc18-1581
American Diabetes Association (ADA) - Standards of Medical Care in Diabetes. Diabetes Care, 2024. Available at: https://diabetesjournals.org/care
Danne T. et al. - International Consensus on Use of Continuous Glucose Monitoring. Diabetes Care, 2017. DOI: 10.2337/dc17-1600

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