[How to measure glycemic instability?].

Instability of glycemic levels is "normal" in type 1 diabetes, with different levels of severity, up to the restrictive definition of brittle diabetes (repeated ketoacidosis and/or severe hypoglycemias). Quantification of glycemic instability, in terms of intraday variability and day-to-day reproducibility, is advisable. Standard deviation of blood glucose, though a simple index does not discriminate between slow and brutal variations. Repartition of blood glucose values also only indicates dispersion. M values compares the patient values to an ideal blood glucose level, emphasizing the role of low values. The MAGE index measures the amplitude of the largest glucose excursions, thus evaluating appropriately glycemic variability. The Low Blood Glucose Index (LBGI) is a new index of variability emphasising (as the M value) the low glycemias. Each glycemia is given a value from O (if >=110 mg/dl) to 100 (if 20 mg/dl). It thus integrates the frequency and severity of hypoglycemias. According to its authors the LBGI would be the best indicator of severe hypoglycemias. The Mean of Daily Differences (MODD) evaluates the day-to-day reproducibility of blood glucose values. All the above indexes could easily be incorporated in the programmes of large memory glucose meters.