Rapid measurement of tacrolimus in whole blood by paper spray-tandem mass spectrometry (PS-MS/MS)

• Paper Spray ionization coupled with tandem mass spectrometry for tacrolimus TDM was evaluated.
• The method uses a simple automated apparatus to generate tacrolimus ions and introduce them into mass spectrometry.
• The method simplifies the use of mass spectrometry in clinical laboratories, without the need of HPLC and sample preparation.
• The method is rapid, accurate and precise, suitable for clinical diagnostic use.
• The method is equivalent in performance to more expensive FDA approved immunoassays.

BackgroundLiquid chromatography-tandem mass spectrometry (LC-MS/MS) provides sensitivity and specificity for monitoring tacrolimus drug level in blood, but it requires an LC system and sample preparation, which is not amenable to random access testing typical of immunoassays. Paper spray (PS) ionization generates gas phase analyte ions directly from dried blood spots without sample preparation and LC. We evaluated a PS-MS/MS method for tacrolimus drug monitoring in a clinical diagnostic laboratory.MethodsWhole blood sample was mixed with stable isotope labeled internal standard ([13C, 2H2]-FK506) and spotted onto a cartridge containing triangular shaped card paper. After drying, samples were analyzed by PS MS/MS in the selected reaction monitoring (SRM) mode, with a run time of 3 min/sample.ResultsAnalytical measurement range was 1.5–30 ng/ml. Assay inter-day imprecision was 13%, 8%, and 5% at tacrolimus concentrations of 4.5, 10.5, and 24.5 ng/ml, respectively. Accuracy was determined by pure tacrolimus solution and was confirmed by result correlation to an immunoassay (slope = 1.0, intercept = − 0.02; r2 = 0.99), and to a conventional LC-MS/MS method (slope = 0.90, intercept = 0.4; r2 = 0.94).ConclusionsPS-MS/MS provides accurate results for tacrolimus with rapid turnaround time amenable to random access testing protocols.