362-OR: The Biological Variability of the BETA-2 Score in Islet Transplant Recipients

Abstract

Background: The BETA-2 score is a validated composite measure of beta cell function in islet transplantation. It is calculated from a fasting sample and lends itself to regular monitoring of islet graft function. To determine whether changes in the BETA-2 score are significant, it is important to understand inherent variability of the score. The aim of this study was to characterize the biological variability (coefficient of variation (CV)) of the BETA-2 score and to define the critical difference (CD) for the score which is the percentage change in score that reflects a significant change in islet function. Methods: Islet transplant recipients with stable graft function were included in this retrospective study. BETA-2 score was calculated weekly over 8 consecutive weeks and the CV was calculated based on the root mean square method. The CD at the 95% confidence limit was calculated as follows: CD = 2.8 x CV. Results: 21 transplant recipients were included of whom 6 were insulin dependent and 15 were insulin independent. These patients also varied in terms of kidney function: 10 subjects with eGFR ≥ 60 (76 ± 14 ml/min/1.73 m2) and 11 subjects with eGFR < 60 (44 ± 10 ml/min/1.73 m2). The CV for all patients was 9.3%, 95% CI [8.7, 10.0]. The CV was similar between insulin independent and insulin dependent subjects (9.0%, 95% CI [8.1, 9.9] vs. 10.2, 95% CI [9.3, 11.1], p=0.5), as well as between subjects with eGFR > 60 vs. eGFR < 60 (8.9%, 95% [8.1,9.8] vs. 9.7%, 95% CI [8.7,10.7], p=0.6). The critical difference for the BETA-2 score was 26.2% for all subjects, 25.1% for insulin independent subjects, 28.5% for insulin dependent subjects, 24.9% for those with eGFR>60, and 27.9% for those with GFR <60. Conclusions: The biological variability of the BETA-2 score appears stable across various clinical scenarios and a minimum difference of 26% between scores appears to constitute a significant change in BETA-2 score. Further analysis including more subjects and a greater range of kidney function is warranted. Disclosure R. Millott: None. R.A. Oram: None. S. Forbes: None. A. Shapiro: Consultant; Self; Viacyte, Inc. P.A. Senior: None. A. Lam: None.