Fast LC-MS/MS analysis of tacrolimus, sirolimus, everolimus and cyclosporin A in dried blood spots and the influence of the hematocrit and immunosuppressant concentration on recovery

The observed HT effect during the validation appeared to be negligible during the correlation study as no concentration corrections for the HT values were needed. Nevertheless, results from DBS samples with extremely high concentrations combined with extremely low HT values should be interpreted with caution. The patient correlation study showed good correlations with R2 values higher than 0.87 between venous whole blood and venous DBS samples were observed for all four immunosuppressants. The Passing & Bablok plots showed positive biases of the slopes of 18% for tacrolimus and less than 12% for sirolimus, everolimus and cyclosporin A. The validated method, proved stability of the immunosuppressants in DBS, and the correlation study showed the capability of the DBS method to be used as an alternative for whole blood analysis in therapeutic drug monitoring.