Reducing the cost of cyclosporin assays: modification of the EMIT 2000 method

Cyclosporin is the leading immunosuppressant agent in organ transplantation, and therapeutic drug monitoring forms an integral part of patient management in most institutions. In the authors' laboratory, the cost of cyclosporin assays represents a major fraction of total consumable expenditure. At present, an average of 4,300 patient cyclosporin assays are performed annually using the EMIT 2000 method (Behring-Syva) on the Cobas Mira analyser (Roche), at a cost of AUD$50,000 in kits alone. As a means of reducing laboratory costs, the manufacturer's recommended method was modified by decreasing all of the reagent and sample volumes in the "Analytical" section of the Cobas Mira cyclosporin programme by 33%. Assay performance was monitored over a 10-month period and compared to that of the unmodified method. Calibration curves were stable, requiring a one-point correction on average of once every 12 days, and a full calibration once ever 1.7 months. Interassay variability was not different to that previously reported for the unchanged method, with mean (SD, CV) concentrations for trilevel quality control specimens of 86.5 micrograms/L (10.2, 11.9%), 185.9 micrograms/L (11.4, 6.2%) and 408.5 micrograms/l (28.9, 7.1%). From 24 specimens assayed in an international quality assurance programme, the results of 23 were within 1.2 SD of the group mean for the EMIT method, with an average bias of 0.8%. With the current modifications, we were able to perform an average of 105 patient assays per kit compared to the previous 71, equating to an annual saving the AUD$16,600.