Monitoring of cyclosporin A levels with radioimmunoassay in renal transplant recipients: comparison of monospecific and nonspecific assays.

Patients receiving cyclosporin A (CsA) therapy should be monitored carefully in order to avoid side effects and maintain immunosuppression. Radioimmunoassay is one of the most commonly used methods of monitoring CsA levels. The decision to use whole blood vs plasma or monospecific vs nonspecific monoclonal antibodies for the measurement of CsA levels has been a controversial issue. In this study, CsA levels in the whole blood and plasma were measured simultaneously with INCSTAR specific monoclonal antibodies in 20 renal transplant recipients (group A). There was a significant correlation between the CsA levels in the whole blood and plasma (R2 = 0.7379, p < 0.00001). However, at the therapeutic limit, the correlation was not good. The whole blood/plasma CsA concentration ratios were not correlated with the hematocrits of the patients. In another group of 20 renal transplant recipients (group B), CsA levels in whole blood and plasma were measured simultaneously with INCSTAR nonspecific monoclonal antibodies. There was a significant correlation between the CsA levels in whole blood and plasma (R2 = 0.6714, p < 0.00001). The whole blood/plasma ratios were significantly correlated with the hematocrits (R2 = 0.5457, p = 0.0002). The later finding could be due to the extensive cross-reactivity of nonspecific monoclonal antibodies with CsA metabolites, which are almost exclusively bound to the erythrocytes. The hematocrits in renal transplant recipients usually show significant change over a period of time. The plasma level may be more stable in such cases. However, measurement of whole blood levels also has several advantages, mainly from a technical aspect.(ABSTRACT TRUNCATED AT 250 WORDS)