Assessment of variables contributing to cyclosporine distribution in blood

Factors which can account for the poor correlation between whole blood and plasma Cyclosporine (CsA) levels in patients on CsA prophylaxis are evaluated. The study took account of the influence of plasma separation procedures, and the sample haematocrit on CsA distribution in the blood of renal transplant patients (n = 35). CsA was measured using both specific and non-specific CsA radioimmunoassays. Significant negative correlations occurred between CsA distribution and the haematocrit, independently of the plasma separation procedure or the specificity of the assay. All results were lower when using the specific assay but a significantly higher percentage of CsA was measured in the plasma by specific assay compared to nonspecific assay when plasma was separated at both 22 degrees C (t-test, p less than 0.02) and at 37 degrees C, p less than 0.01). This may relate to the selective binding of CsA and its analogues by blood cells. This study is a prelude to the development of more consistent plasma separation procedures in the monitoring of this drug.