OBJECTIVES: This study evaluated the analytical characteristics of the new Abbott microparticle enzyme immunoassay (MEIA) for sirolimus. DESIGN AND METHODS: The protocol consisted of nine sections: evaluation of antibody specificity, linearity, detection limit, quantification limit, endogenous interferents, exogenous interferents, precision, proficiency testing panel, and method comparison. RESULTS: The mean analytical detection limit was 0.68 microg/L. The sirolimus concentration corresponding to a total CV of 20% was 1.5 microg/L. Linearity of response was demonstrated across the dynamic range of the assay. Total precision (CVs) at QC control levels from 5 to 22 microg/L ranged from 5.7 to 12.6%. Assay standardization was found to be in good agreement with LC/MS/MS as compared with target values for spiked sirolimus proficiency samples from an international sirolimus proficiency testing program. Good correlations (R values) of the immunoassay were observed in comparisons to LC/MS/MS. R values tended to be lower in comparisons with LC/UV methods. Across both LC-based methods and all study sites, there was approximately 25% overall positive slope bias due to cross reactivity of the MEIA antibody to metabolites of sirolimus. The assay cross-reactivity to metabolites of sirolimus parent drug ranged from 6 to 63%. Assay interferences were minimal with the exception of hematocrit, which presented a negative relationship to measured sirolimus concentration. CONCLUSIONS: The MEIA demonstrated acceptable analytical characteristics for use for routine monitoring of sirolimus immunosuppressive therapy, and is a viable alternative to HPLC-based methods for sirolimus monitoring.
OBJECTIVES: This study evaluated the analytical characteristics of the new Abbott microparticle enzyme immunoassay (MEIA) for sirolimus. DESIGN AND METHODS: The protocol consisted of nine sections: evaluation of antibody specificity, linearity, detection limit, quantification limit, endogenous interferents, exogenous interferents, precision, proficiency testing panel, and method comparison. RESULTS: The mean analytical detection limit was 0.68 microg/L. The sirolimus concentration corresponding to a total CV of 20% was 1.5 microg/L. Linearity of response was demonstrated across the dynamic range of the assay. Total precision (CVs) at QC control levels from 5 to 22 microg/L ranged from 5.7 to 12.6%. Assay standardization was found to be in good agreement with LC/MS/MS as compared with target values for spiked sirolimus proficiency samples from an international sirolimus proficiency testing program. Good correlations (R values) of the immunoassay were observed in comparisons to LC/MS/MS. R values tended to be lower in comparisons with LC/UV methods. Across both LC-based methods and all study sites, there was approximately 25% overall positive slope bias due to cross reactivity of the MEIA antibody to metabolites of sirolimus. The assay cross-reactivity to metabolites of sirolimus parent drug ranged from 6 to 63%. Assay interferences were minimal with the exception of hematocrit, which presented a negative relationship to measured sirolimus concentration. CONCLUSIONS: The MEIA demonstrated acceptable analytical characteristics for use for routine monitoring of sirolimus immunosuppressive therapy, and is a viable alternative to HPLC-based methods for sirolimus monitoring.