Background: The purpose of this study was to investigate relationship between tacrolimus intraindividual variability (IIV), acute microinflammation (AMI) based on 1 year-transplanted kidney biopsy, and biopsy-proven acute rejection (BPAR).

Method: Data from renal transplant patients were analyzed retrospectively between Jan 2007 and Dec 2014. A total of 678 adult patient received tacrolimus-based immunosuppression for 1 year after kidney transplantation, and 213 patients out of them had a result of first 1 year transplanted kidney biopsy. The tacrolimus IIV and mean tacrolimus trough concentration were calculated from the tacrolimus trough concentrations between 6 and 12 months after kidney transplantation. The patients were divided into low and high tacrolimus IIV groups according to rounded off median value of tacrolimus IIV (16.0%).

Results: The median IIV of the 678 patients was 15.6 %. BPAR occurred in 124 cases (18.3%) during the follow-up period. There was significantly different between low and high IIV group (15.7% vs 21.2%, p-value 0.040). Score of microvascular inflammation (MVI) did differ significantly between two groups (0.41±0.77. vs 0.57±0.82, p-value 0.029). The time to occurring AR of low IIV group is statistically longer than high IIV group (38.0±1.97 vs 29.1±1.74 months, p-value 0.001) In subgroup analysis, mean of mean Tac trough concentration of the 213 did not differ between two groups (low IIV 6.5±1.1 vs high IIV 6.8±1.39, p-value 0.109). The BPAR, and score of acute lesion, and score of chronic lesion between two groups were no significant difference statistically. (18.6% vs 18.0%, 1.4±1.47 vs. 1.60±1.76, 1.7±1.60 vs 2.00±1.80, p-value, 0.528, 0.132, 0.103) Scores of MVI of high IIV group was higher than low IIV group statistically (0.19±0.46 vs. 0.38±0.62, p-value 0.011). However, the allograft outcomes including graft loss, death, creatinine, and GFR between low and high IIV groups were no differences.

Conclusion: High IIV group of Tac has tendency that scores of acute and chronic lesion are higher than low IIV. They are associated with increasing incidence of BPAR and higher scores of MVI. In addition, high IIV has a significant association with MVI based on post-1 year kidney biopsy. Considering that size of this study, large-scale study is needed to investigate association with MVI and BPAR, graft survival.

CITATION INFORMATION: Kim S.-Y, Min S.-I, Cho W, Cho S, Cho M.-J, Ahn S, Min S.-K, Ha J. Association with Tacrolimus Intraindividual Variability, Acute Microinflammation Based on 1 Year-Transplanted Kidney Biopsy After Transplantation, and Biopsy-Proven Acute Rejection. Am J Transplant. 2017;17 (suppl 3).

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