Background: A high degree of intrapatient variability (IPV) of tacrolimus blood concentrations has been associated with poor long-term outcome (1). Periods of under-exposure with increased risk of acute rejection is a possible underlying explanation.

Methods: For 250 patients in this retrospective single-centre study the coefficient of variance (CV) was calculated as a measure for IPV by using whole-blood tacrolimus concentrations drawn during the first three months after transplantation. Cases were split into high and low variability using the median CV and these groups were compared. The primary outcome was biopsy-proven acute rejection, defined as at least Banff grade 1, including subclinical rejection detected in a routine three month post-transplant protocol biopsy. This study received ethical approval from the host site.

Results: Of the 125 patients in each subgroup, biopsy-proven acute rejection was observed in 22 (20.95%) and 39 (31.20%) patients with a low and high CV for tacrolimus concentration IPV, respectively (p=0.0295). Patients of black ethnicity were more frequently observed in the high CV (n=23, 18.4%) versus low CV (n=11, 8.8%) group (p=0.0396).

Conclusion: This study demonstrates a significant association between a high IPV of tacrolimus concentrations in the first three months following renal transplant and biopsy-proven acute rejection.

References:

1. Borra LC, Roodnat JI, Kal JA, et al. High within-patient variability in the clearance of tacrolimus is a risk factor for poor long-term outcome after kidney transplantation. Nephrol Dial Transplant 2010;25(8):2757-63.

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