The measurement of immunosuppressive drugs by mass spectrometry and immunoassay in a South African transplant setting

Abstract

Objectives: Liquid chromatography tandem mass spectrometry (LCMS/MS) is the gold standard for measurement of immunosuppressive drugs (ISDs), but is technically demanding and less accessible in resource-limited countries. Immunoassays can also measure ISD concentrations, but may be limited by cross-reactivity. We evaluated the performance of the Roche electrochemiluminescence immunoassay (ECLIA) for cyclosporine, everolimus and sirolimus against LCMS/MS in an African population for the first time. Methods: Bias for ECLIA was estimated by comparing ECLIA-measured ISD concentrations to those obtained by LCMS/MS in 42, 43 and 47 patient samples for cyclosporine, everolimus and sirolimus, respectively. Precision was assessed by performing replicate measurements of quality control materials. Results: Deming regression analysis for all ISDs showed strong correlation between ECLIA and LCMS/MS with a Pearson’s r of > 0.94. The slopes for cyclosporine, everolimus and sirolimus were 0.94 [95% CI: 0.87 – 1.03], 1.35 [95% CI: 1.23 – 1.44] and 0.96 [95% CI: 0.85 – 1.15] with y-intercepts of 31.60 μg/L [95% CI: 2.02 – 57.63], 0.23 μg/L [95% CI: -0.21 – 0.72] and 2.61 μg/L [95% CI: 1.30 – 3.56], respectively. Difference plots showed a median bias of 2.07% [95% CI: -1.42 – 6.99%], 41.2% [95% CI: 34.9 – 51.8%] and 34.9% [95% CI: 28.4 – 47.3%] for cyclosporine, everolimus and sirolimus, respectively. Conclusions: The cyclosporine ECLIA yielded results comparable to LCMS/MS while poorly comparable results were obtained for everolimus and sirolimus, which may be explained by ISD metabolite cross-reactivity, amongst other factors. The poor comparability, although not unique, is noteworthy and the clinical consequences of these differences require further investigation.