Abstract

Background Tacrolimus (Tac) intraindividual variability (TacIPV) in pediatric kidney transplant patients is only poorly understood. We investigated the impact of TacIPV on de novo donor-specific HLA antibodies (dnDSA) development and allograft rejection in Caucasian pediatric recipients of a living or deceased donor kidney with low immunological risk. Methods This was a single-center retrospective study including 48 pediatric kidney transplant recipients. TacIPV was cal- culated based on coefficient of variation (CV%) 6–12 months posttransplant. TacIPV cutoff was set at the median (25%). Outcome parameters were dnDSA development and rejection episodes. Results In total, 566 Tac levels were measured with median 11.0 (6.0–17.0) measurements per patient. The cutoff of 25% corresponded to the median CV% in our study cohort (25%, IQR 18–35%) and was comparable to cutoffs determined by receiver operating characteristic (ROC) curve analysis. High TacIPV was associated with higher risk of dnDSA develop- ment (HR 3.4, 95% CI 1.0–11.1, P = 0.047; Kaplan–Meier analysis P = 0.018) and any kind of rejection episodes (HR 4.1, 95% CI 1.1–14.8, P = 0.033; Kaplan–Meier analysis P = 0.010). There was a clear trend towards higher TacIPV below the age of 6 years. TacIPV (CV%) was stable over time. A TacIPV (CV%) cutoff of 30% or IPV quantification by mean absolute deviation (MAD) showed comparable results. Conclusions High TacIPV is associated with an increased risk of dnDSA development and rejection episodes > year 1 posttransplant even in patients with low immunological risk profile. Therefore, in patients with high TacIPV, poten- tial causes should be addressed, and if not resolved, changes in immunosuppressive therapy should be considered.