Continuous Glucose Monitoring after Islet Transplantation in Type 1 Diabetes: An Excellent Graft Function (β-Score Greater Than 7) Is Required to Abrogate Hyperglycemia, Whereas a Minimal Function Is Necessary to Suppress Severe Hypoglycemia (β-Score Greater Than 3)

Context: For the last 10 yr, continuous glucose monitoring (CGM) has brought up new insights into the accuracy of blood glucose analysis. Objective: Our objective was to determine how islet graft function was able to influence the various components of dysglycemia after islet transplantation (IT). Design and Setting: We conducted a single-arm open-labeled study with a 3-yr follow-up in a referral center (ClinicalTrial.gov identifiers NCT00446264 and NCT01123187). Patients: Twenty-three consecutive patients with type 1 diabetes (14 islet alone, nine islet after kidney) received IT within 3 months using the Edmonton protocol. Intervention: Intervention included 72-h CGM before and 3, 6, 9, 12, 24, and 36 months after transplantation. Main Outcome Measure: Graft function was estimated via β-score, a previously validated index (range 0–8) based on treatment requirements, C-peptide, blood glucose, and glycated hemoglobin. Results: At the 3-yr visit, graft function persisted in 19 patients (82%), and 10 (43%) remained insulin independent. Glycated hemoglobin decreased in the whole cohort from 8.3% (7.3–9.0%) at baseline to 6.7% (5.9–7.7%) at 3 yr [median (interquartile range), P < 0.01]. Mean glucose, glucose sd, and time spent with glycemia above 10 mmol/liter (hyperglycemia) and below 3 mmol/liter (hypoglycemia) were significantly lower after IT (P < 0.05 vs. baseline). The four CGM outcomes were related to β-score (P < 0.001). However, partial function (β-score >3) was sufficient to abrogate hypoglycemia; suboptimal function (β-score >5) was necessary to significantly improve mean glucose, glucose sd, and hyperglycemia; and optimal function (β score >7) was necessary to normalize them. Conclusion: The four components of dysglycemia were not equally affected by the degree of islet graft function, which could have important implications for future development of β-cell replacement. A β-score above 3 dramatically reduced the occurrence of hypoglycemia.