GRI (glycemia risk index) calculator from glucose sensor data

The glycemia risk index (GRI) is a score from 0 to 100 that shows how well blood glucose is controlled, taking into account both hypoglycemia and hyperglycemia [2] [3]. The lower the score, the better the glucose control [3]. The index is calculated from the values received from the sensor over at least the last 14 days [3].

A single number is easier to follow from one report to the next than several percentages [2]. The score combines the time spent in each glucose range, with a weight set by diabetes specialists [2]. In children and adolescents with type 1 diabetes, a higher score is associated with a higher HbA1c, including in the following months [4]. In adults with type 1 diabetes, a higher score is associated with a poorer quality of life and more diabetes-related stress [5].

Hypoglycemia counts more in the score than hyperglycemia [2]. A blood glucose below 54 mg/dL (3.0 mmol/L) is hypoglycemia that must be treated immediately. From this threshold, the symptoms of glucose shortage in the brain begin to appear [1]. In each of the two parts of the score, values far from the target count more than values close to the target [2].

The calculation multiplies the time spent in each range, as a percentage, by the weight of that range and adds up the results [2]. The highest weight belongs to the time below 54 mg/dL (3.0 mmol/L) and the lowest to the time between 181 and 250 mg/dL (10.1–13.9 mmol/L) [2]. One percent of time in the first range raises the score almost four times more than one percent in the second [2]. The maximum score is 100, even if the result of the calculation exceeds this value [2].

The zones divide the score into five equal steps, from A, the best glucose control, to E, the poorest [2]. Zone A covers scores 0–20, zone B 21–40, zone C 41–60, zone D 61–80 and zone E 81–100 [2]. If your time in each range is exactly at the limit of the targets recommended for most adults, the score is around 34, in zone B [1] [2]. A score in zone B therefore does not mean poor glucose control.

The calculator also shows how much of the score comes from hypoglycemia and how much from hyperglycemia [2]. If the time below 70 mg/dL (3.9 mmol/L) exceeds your target, you need to tell your medical team without waiting for your next appointment. This applies even if the score comes mostly from hyperglycemia [1]. In children with type 1 diabetes, an automated insulin delivery (AID) system can reduce the time spent in hypoglycemia and in hyperglycemia [6].

The data should be taken from your sensor report covering at least the last 14 days, usually the ambulatory glucose profile (AGP) [1] [3]. The report is reliable if the sensor was active for at least 70% of this period [1]. From it you need to copy the time spent in the four ranges outside the target, two below 70 mg/dL (3.9 mmol/L) and two above 180 mg/dL (10.0 mmol/L).

Some apps show only the total time below 70 mg/dL (3.9 mmol/L) or above 180 mg/dL (10.0 mmol/L). In this case, the time below 54 mg/dL (3.0 mmol/L) must be subtracted from the first total and the time above 250 mg/dL (13.9 mmol/L) from the second. The score was built for, and is recommended for, people treated with insulin [2] [3]. For people not treated with insulin, its usefulness is not yet established [3].