The Good, Bad and Ugly: Drug Testing in Liver Transplant Evaluations

Alcohol-related liver disease is the most common indication for liver transplantation but only 5% of patients with end stage liver disease receive transplantation, with ethical concerns about allocation of scarce resources to individuals with substance-induced liver disease a contributing factor. In addition, since most transplant centers require a period of abstinence before considering candidates for organ listing, transplant teams are often required to obtain drug tests without necessarily understanding how best to interpret results in various clinical circumstances or the impact on eligibility criteria. Furthermore, since other tests including a patient’s self-report are not always a reliable indicator of recent drug or alcohol use, lack of good alternatives can result in over-reliance on drug testing alone to verify abstinence. Addiction specialists can help guide liver transplant services on how best to interpret drug or metabolite levels and be a critical component of a patient’s treatment of substance use in liver transplant evaluations. This focus session will discuss the two most commonly encountered substances used by patients with alcohol-related liver disease undergoing liver transplant evaluation with emphasis on how variabilities in drug or metabolite levels and co-morbidities like obesity complicate interpretation of these results and potentially subject patients to further testing that may not be accurate, useful or prognostic. While several biomarkers detecting alcohol consumption currently exist, a higher specificity compared to other tests, longer half-lives of 4-12 days, and detection windows of 2-4 weeks has led to phosphatidylethanol (PeTH) being increasingly used in major transplant centers. Like other biomarkers, however, PeTH tests are subject to internal variability, and patients with advanced liver disease may have falsely elevated PeTH concentrations that don’t necessarily reflect exogenous alcohol consumption. This focus session will cover PeTH kinetics, factors contributing to false positive results and ways to improve the utilization of testing. Similarly, another important issue in patients being considered for liver transplantation is the ability to distinguish recent from previous cannabis use. Extremely long tetrahydrocannabinol and metabolite detection times of up to 77 days from last use have been reported. Variations in detection time are dependent on several factors, including hydration state, metabolism and body mass index. Use of a creatinine-corrected THCCOOH concentration can potentially help detect subtle differences in drug levels and be particularly useful in patients undergoing liver transplant evaluation. This didactic session will synthesize the medical evidence regarding detection times for cannabinoids, describe THC pharmacokinetics and pharmacodynamics and other testing options in pre and post -liver transplant evaluations.