Falsely Elevated Tacrolimus Concentrations Drawn From a Central Line in a Pediatric Heart Transplant Patient

There have been reports of falsely elevated calcineurin inhibitor concentrations when drawn from a central line through which the drug was administered due to adsorption to the internal lumen. Tacrolimus, used for immunosuppression in pediatric heart transplant patients, is one such medication. This report describes the case of a 3-year-old male with a history of orthotopic heart transplant (OHT) who was admitted to the intensive care unit with acute respiratory failure secondary to presumed community-acquired pneumonia and concern for septic shock. His hospital course was prolonged and complicated, requiring periods of nothing by mouth and intravenous (IV) tacrolimus, which was administered through a central line. Whole blood tacrolimus trough concentrations from the central line were elevated and highly variable without correlation to concentrations drawn from venipuncture, resulting in improper tacrolimus dose adjustments. Ultimately, peripheral concentrations were exclusively used to ensure the patient received adequate dosing. We observed persistently discordant drug concentrations drawn from the central line weeks after central IV drug administration was stopped. Fortunately, no graft dysfunction or rejection occurred during the hospital course. To our knowledge, this is the first report that describes clinical outcomes in a pediatric heart transplant patient whose tacrolimus concentrations were inconsistent between central and peripheral lines as well as methods to rehabilitate the central line. Providers must recognize medications that may adsorb to catheter materials, causing sample contamination and resulting in falsely elevated drug concentrations as well as the potential for cross contamination between lumens. Familiarity will help patients avoid extraneous medical workup, suboptimal treatment, and risk of organ rejection.