OBJECTIVE: Islet transplantation was recently US Food and Drug Administration approved for adults with type 1 diabetes complicated by recurrent severe hypoglycemia events (SHEs). We sought to understand the long-term benefit for glycemic control and risk of immunosuppression to kidney function associated with islet transplantation compared with ongoing standard of care. RESEARCH DESIGN AND METHODS: We performed a case-control analysis of prospectively collected data from patients in the Collaborative Islet Transplant Registry (CITR) with at least one SHE in the year (2000-2014) before transplantation (cases) and compared them with data from patients in the T1D Exchange (T1DX) Registry with at least one SHE in the year (2010-2012) before enrollment (controls), with both cohorts observed over 5 years. SHEs were restricted to those resulting in seizure or loss of consciousness. RESULTS: Cases from CITR (n = 71) compared with controls from T1DX (n = 213) more often achieved the primary outcome of HbA1c <
7.0% and absence of an SHE (71-80 vs. 21-33% over 5 years
P <
0.001) and the outcome of HbA1c ≤6.5% and absence of an SHE (60-75% vs. 10-20%
P <
0.001) while requiring significantly less insulin (majority in CITR were insulin independent). Kidney function, measured by estimated glomerular filtration rate, declined from baseline to a greater extent in CITR than in T1DX (-8.8 to -20 vs. -1.3 to -6.5 mL ⋅ min-1 ⋅ 1.73 m-2 over 5 years
P <
0.001). CONCLUSIONS: Islet transplantation for adults with type 1 diabetes complicated by SHEs results in near-normal glycemic control in the absence of SHEs more often than observed with standard of care, but at the cost of greater reduction in kidney function.