Capillary blood, dried on filter paper, as sample for monitoring cyclosporin A concentrations

For monitoring the immunosuppressive drug cyclosporin A by radioimmunoassay (Sandoz Ltd.) we propose a simple method of sampling in which 20 microL of capillary blood is dried on filter paper. Patients can collect their own samples and mail or bring them to the laboratory. Results for such samples, and their variability, correspond to those for conventional methods of sampling (collection of venous or capillary blood into buffer). Capillary blood can be stored on paper at room temperature for more than four weeks with no effect on assay results.