Shah PB, et al. - Given that risk for de novo donor-specific antibody formation and death-censored graft failure among kidney transplant recipients is conferred by within-patient tacrolimus level variability > 30%, researchers analyzed a large national data set in order to determine the burden of tacrolimus variability as well as the correlation between variability and subtherapeutic tacrolimus levels. All tacrolimus levels, with a diagnosis code for kidney transplant, drawn at LabCorp facilities in the United States between November 2011 and September 2017, were evaluated. The values that could represent new allografts were excluded. Among established kidney transplant patients, more than half showed levels of tacrolimus variability that have been related to inferior transplant outcomes. Findings revealed a weak link of tacrolimus variability with subtherapeutic levels but tacrolimus variability was viewed as a more complex constellation of clinical factors.