Measurement of cyclosporine concentrations in whole blood: HPLC and radioimmunoassay with a specific monoclonal antibody and 3H- or 125I-labeled ligand compared.

We compared cyclosporine concentrations in whole blood as measured by HPLC and by RIA with a monoclonal antibody specific for cyclosporine with 3H- or 125I-labeled cyclosporine ligand. The 3H-RIA kit slightly underestimated cyclosporine concentrations (greater than 600 micrograms/L) in comparison with HPLC. Over a wide range of concentrations, cyclosporine measured with the 125I-RIA kit correlated well with HPLC (slope = 0.99, n = 301, r = 0.98), observed for samples from recipients of kidney, heart, or liver allografts (respective slopes: 1.01, 0.93, and 1.00). The 125I-RIA standard curve was linear to 1000 micrograms of cyclosporine per liter. Inter- and intra-assay CVs for 125I-RIA measurements of cyclosporine were less than or equal to 7%. Evidently, the 125I-RIA kit involving a monoclonal antibody specific for cyclosporine is equivalent to the HPLC assay and can replace it for therapeutic drug monitoring of cyclosporine therapy.