Determination of Calcineurin Inhibitors in Dried Blood Spots from Kidney Transplant Recipients

Background: Determination of cyclosporine A (CsA) and tacrolimus (Tac) in dried blood spots (DBS) could enable drug monitoring in transplanted patients without the necessity of having to take venous blood samples. Therefore, we have developed a method for quantitative determination of calcineurin inhibitors (CNI) by liquid-chromatography-tandem mass spectrometry (LCMS). Methods: In a study with 68 kidney transplant recipients (KTR, 34 CsA, 34 Tac), we tested the clinical application of LCMS monitoring in DBS in comparison to LCMS in whole blood. Results: The measuring range is proven for 27.33 to 1345 ng/ml for CsA and for 1.63 to 39.7 ng/ml for Tac. The requirements for clinical chemical analyses for precision and accuracy are complied with. Stability is documented for a period of 14 days. The study showed the following deviations from LCMS in whole blood for determination of CsA and Tac in DBS after introducing a correction factor by the haematocrit (Hct) value (CsA trough level: mean = 4.7%, ±1.96 standard deviation (SD) −52.1% to 61.4%, N = 96; CsA peak level: mean = 7.3%, ±1.96 SD −39.7% to 54.4%, N = 95; Tac trough level: mean = −0.5%, ±1.96 SD −76.4% to 75.3%, N = 88; Tac peak level: mean = 3.9%, ±1.96 SD −80.1% to 88.7%, N = 92). Conclusions: Our data show comparable results with the reference method by means of LCMS in whole blood. Therefore, DBS of KTR for determination of CNI levels could be transported on filter cards by mail to the respective laboratory resistant to breakage and the hazard of infection.