Analysis of Tacrolimus Trends and Trough Levels < 5 ug/L Preceding Development of Biopsy Proven Acute Rejection in Renal Transplant Patients

Abstract

British Columbia Transplant (BCT) modified the tacrolimus (TAC) target guideline for patients beyond 6 months post-transplant from 4–6 µg/L to 5–7 µg/L in 2021. Although TAC is the mainstay medication used in the prevention of allograft rejection in kidney transplants, optimal target concentration is still being actively researched and guidelines differ locally. This retrospective case series as a part of a QI project aims to explore the relationship between TAC values < 5 µg/L and the occurrence of biopsy proven acute rejections (BPAR). TAC and serum creatinine values one-year leading to BPAR were collected from 6 patients (PT1–6) in total. One out of the six patients showed TAC trough mean significantly < 5 µg/L (P = 0.0002) while four out of six patients experienced levels < 5 µg/L on at least one occasion. It is observed that baselinealtering drops in TAC were consistently followed by measurable renal function decline which is a potential determinant of BPAR. Further, TAC variability in patients is suggested as a contributing factor for rejections. The previous guideline of 4 µg/L minimum is seen to be effective in some patients and insufficient in others. In result, targeting > 5 µg/L may be beneficial to a wider range of patients when used as a general guideline.