Application of a Fully Automated Dried Blood Spot Method for Therapeutic Drug Monitoring of Immunosuppressants

Context.-The follow-up of patients under lifelong immunosuppressant therapy is pivotal to prevent allograft rejection after transplant. Part of the difficulties associated with routine monitoring of immunosuppressant concentrations can be alleviated by home sampling using dried blood spots (DBSs).Objective.-To evaluate the applicability of a DBS method for the determination of immunosuppressants in venous blood samples, making use of an automated extraction platform.Design.-Paired venous DBSs and whole blood samples were analyzed for tacrolimus (n =162), sirolimus (n = 47), everolimus (n = 45), and cyclosporin A (n = 61) with liquid chromatography coupled to tandem mass spectrometry, using fully automated extraction for DBSs. Agreement between the automated DBS and whole blood method was assessed by using Bland-Altman comparison. Both an analytical and a clinical acceptance limit were predefined at more than 67% of all paired samples within 20% of the mean of both samples and more than 80% of all paired samples within 20% of the whole blood concentration, respectively.Results.-An impact of the hematocrit (hct) on DBS quantitation was observed for all analytes, which could be alleviated for all analytes by using a hct conversion formula based on a tacrolimus data subset: [DBScorrected] = [DBSmeasured]/(1.6305 - 1.559*hct). After correction, both analytical and clinical acceptance criteria were met for all analytes.Conclusions.-Automated DBS analysis shows great potential for routine therapeutic drug monitoring of immunosuppressants, avoiding any manual sample han-dling.