A comparison of cyclosporine assays using sequential samples from selected transplant patients

The monitoring of cyclosporine (CsA) whole blood concentrations is an integral part of immunosuppressive treatment with this drug. Although such monitoring has been facilitated by the introduction of monoclonal immunoassay techniques, there is a paucity of published data comparing the assays longitudinally in selected patients. The purpose of our study was to co-evaluate two monoclonal immunoassays (Cyclosporine FPIA whole blood assay, Abbott Laboratories; Cyclo-Trac SP-whole blood RIA, Incstar Inc.) and a high-performance liquid chromatography (HPLC) technique for quantitating CsA in sequentially collected trough whole blood samples from 14 patients up to 75 days after renal (n = 6), heart (n = 3), and liver (n = 5) transplantation. HPLC CsA metabolite analyses (AM1, AM9, AM4N) were performed. Although CsA concentrations within most patients were significantly higher (p < 0.05, paired t test) when measured by both immunoassay techniques compared to HPLC, levels determined in three patients, (one liver, two renal) for the FPIA/HPLC comparison and one patient (liver) for the RIA/HPLC comparison were not significantly different (p > 0.05). CsA levels within nine patients were not significantly different (p > 0.05) when FPIA and RIA were compared, but results within three patients, (one liver, two renal) were significantly higher (p < 0.05) by RIA compared to FPIA, but results within one patient (heart) were significantly higher (p < 0.05) by FPIA. Our results demonstrate first that depending on the patient, HPLC-derived CsA results are not consistently lower than results generated by immunoassay techniques and second that CsA levels obtained by FPIA are statistically equivalent or in some patients, statistically less than RIA-derived levels.