The islet size distribution in a preparation may contribute to islet transplant outcomes. Islets are devascularized cell aggregates that rely on oxygen diffusion from their surfaces, particularly in the early post-transplant period. Oxygen diffusion limitations increase in proportion to islet diameter and this concept can be extrapolated to an entire islet preparation. To test this hypothesis, we studied the impact of islet size index (ISI) on outcomes following islet autotransplantation (IAT) in recipients receiving a marginal islet dose (2000-4999 islet equivalents [IE] per kilogram body weight [kgBW]) from 1/1/2009-6/11/2012 at the University of Minnesota (n=58). ISI was defined as the number of IE divided by the number of islet particles [IN] in a preparation; an ISI below 1 indicates an average islet diameter in a preparation that is lower than 150 ¯o;m. The primary outcome was 6-month insulin use status (independence vs. dependence [partial or complete]).

Median (± interquartile range [IQR]) ISI, proportion of islets >200 ¯o;m in diameter, and islet dose (both total transplanted and per kgBW) are presented as stratified by the post-IAT primary outcome (Table 1). The median ISI was lower for recipients achieving insulin independence at 6-months (0.74 vs. 0.88, p=0.07 via Mann-Whitney test). Univariate logistic regression analysis indicated that IN/kgBW (p=0.003) and ISI (p=0.04) were most strongly correlated with the primary outcome.

Islet size may be an important determinant of post-IAT outcomes, particularly in recipients receiving marginal islet doses. Further analysis must be done to evaluate whether the islet dose in combination with the ISI can enable improved prediction of post-IAT outcomes.

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