Results from a proficiency testing pilot for immunosuppressant microsampling assays

BACKGROUND: Therapeutic Drug Monitoring (TDM) of immunosuppressive drugs is important for the prevention of allograft rejection in transplant patients. Several hospitals offer a microsampling service that provides patients the opportunity to sample a drop of blood from a fingerprick at home that can then be sent to the laboratory by mail. The aim of this study was to pilot an external quality control program.METHODS: Fourteen laboratories from seven countries participated (fully or partly) in three rounds of proficiency testing for the immunosuppressants tacrolimus, ciclosporin, everolimus, sirolimus and mycophenolic acid. The microsampling devices included the following: Whatman 903 and DMPK-C, HemaXis, Mitra and Capitainer-B. All assays were based on LC-MS/MS. In round 2, microsamples as well as liquid whole blood samples were sent, and one of these samples was a patient sample.RESULTS: Imprecision CV% values for the tacrolimus microsamples reported by individual laboratories ranged from 13.2% - 18.2%, 11.7% - 16.3%, and 12.2% - 18.6% for rounds 1, 2, and 3 respectively. For liquid whole blood (round 2), the imprecision CV% values ranged from 3.9% - 4.9%. For the other immunosuppressants, the results were similar. A great variety in analytical procedures was observed, especially the extraction method. For the patient sample, the microsample results led to different clinical decisions compared to that of the whole blood sample.CONCLUSIONS: Immunosuppressant microsampling methods show great interlaboratory variation compared to whole blood methods. This variation can influence clinical decision making. Thus, harmonization and standardization are needed. Proficiency testing should be performed regularly for laboratories that use immunosuppressant microsampling techniques in patient care.