Assessment of tacrolimus and creatinine concentration collected using Mitra microsampling devices

Current practice requires regular venous blood samples for monitoring of tacrolimus concentrations post renal transplant requiring regular hospital visits. Mitra devices use volumetric absorptive microsampling technology and absorb a fixed amount of blood (10 μL) from a capillary blood sample. They are a viable volumetric alternative to dried blood spots and are able to be posted to the laboratory for analysis.

The aim was to develop and validate liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays for tacrolimus and creatinine analysis using Mitra devices. The usefulness of this approach was assessed in renal transplant patients routinely monitored for tacrolimus and creatinine.

Routine tacrolimus samples were used to assess the utility and reliability of Mitra sampling. Shared sample preparation for both tacrolimus and creatinine was carried out in a 96-deep well plate; mass spectrometric analysis was then undertaken for tacrolimus followed by re-injection for creatinine analysis.

Comparison of 131 Mitra samples with a routine LC-MS/MS assay for tacrolimus showed a minimal bias -5.6% (95% CI -8.5 to -2.7%). Comparison of 135 serum and Mitra samples for creatinine using a fully validated LC-MS/MS assay showed a bias -6.5% (95% CI -8.5 to -4.5%).

We have developed assays for tacrolimus and creatinine on fingerprick blood using the Mitra device and believe this approach provides a viable alternative to repeated venepuncture for therapeutic drug monitoring. This method could open up the opportunity for patients to perform tacrolimus and kidney function monitoring at home.