The influence of the dried blood spot drying time on the recoveries of six immunosuppressants

One of the main advantages of DBS sampling is that it allows the patient to sample at home and send the DBS sample to the laboratory by mail [1-4]. This sampling is considered to be patient friendly because it is less invasive and saves patients transportation costs and time. DBS sampling also has a lower biohazard risk and requires a smaller amount of blood than venous sampling [2,4]. Solid organ transplant recipients are required to use a lifetime of immunosuppressant medications like tacrolimus (TaC), sirolimus (SiR), everolimus (EvE) and cyclosporin A (CyA) to prevent allograft rejection. Bioanalysis and Therapeutic Drug Monitoring of these drugs are necessary because efficacy and toxicity is associated with blood concentrations and/or pharmacokinetic parameters. Therefore, these patients could greatly benefit from immunosuppressant DBS analysis. Since the use of dried blood spot (DBS) analysis for therapeutic drug monitoring (TDM), more extensive validation procedures have been proposed in order to improve the quality of the analysis results. Variations of the hematocrit value, spot volume and DBS stability are among the parameters that should be investigated during method validation [1,5]. A perhaps unappreciated source of variability may be the drying time of a dried blood spot sample. After collection of the blood on the DBS card it should be dried dried at ambient temperature. It is already suggested by the European Bioanalysis Forum (EBF) that the required drying time may be influenced by the hematocrit (HT) and that this may affect the robustness and reproducibility of the assay [5]. Consequently it is recommended to investigate these parameters as part of the validation [5]. Although the DBS may appear dry after 3 hours, the extraction recoveries of the substances within the DBS JOURNAL OF APPLIED BIOANALYSIS, October 2015, p. 116-122. http://dx.doi.org/10.17145/jab.15.019 (ISSN 2405-710X) Vol. 1, No. 4