Assessment of the Severity of Hypoglycemia and Glycemic Lability in Type 1 Diabetic Subjects Undergoing Islet Transplantation

Abstract

Currently, the major indications for solitary islet transplantation are recurrent severe hypoglycemia and labile glucose control. Quantifying these problems remains subjective. We have developed a scoring system for both hypoglycemia and glycemic lability, established normative data, and used them in patients who have undergone islet transplantation. A composite hypoglycemic score (HYPO score) was devised based on the frequency, severity, and degree of unawareness of the hypoglycemia. In addition, using 4 weeks of glucose records, a lability index (LI) was calculated based on the change in glucose levels over time and compared with a clinical assessment of glycemic lability. A mean amplitude of glycemic excursions (MAGE) was also calculated based on 2 consecutive days of seven readings each day. These scores were determined in 100 randomly selected subjects with type 1 diabetes from our general clinic to serve as a control group and in patients before and after islet transplantation. The mean age of the control diabetic subjects was 38.4 ± 1.3 years (±SE), with a duration of diabetes of 21.5 ± 1.1 years. The median HYPO score in the control subjects was 143 (25th to 75th interquartile range: 46–423). The LI in the diabetic control subjects was 223 (25th to 75th interquartile range: 130–329 mmol/l²/h · week⁻¹). The LI correlated much more closely than the MAGE with the clinical assessment of lability. A HYPO score of ≥1,047 (90th percentile) or an LI ≥433 mmol/l²/h · week⁻¹ (90th percentile) indicated serious problems with hypoglycemia or glycemic lability, respectively. The islet transplant patients (n = 51) were 42.1 ± 1.4 years old, with a duration of diabetes of 25.7 ± 1.4 years. Islet transplant patients had a mean HYPO score of 1,234 ± 184 pretransplant, which was significantly higher than that of the control subjects (P < 0.001), which became negligible posttransplantation with the elimination of hypoglycemia. The median LI pretransplant was 497 mmol/l²/h · week⁻¹ (25th to 75th interquartile range: 330–692), significantly higher than that of control subjects (P < 0.001), and fell to 40 (25th to 75th interquartile range: 14–83) within a month after the final transplant. In those who had lost graft function, the LI rose again. The HYPO score and LI provide measures of the extent of problems with hypoglycemia and glycemic lability, respectively, complement the clinical assessment of the problems with glucose control before islet transplantation, and will allow comparison of selection of subjects for transplants between centers.