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[Comparison of high-resolution liquid chromatography versus microparticle enzyme immunoassay for the measurement of sirolimus levels in renal transplantation].

OBJECTIVE
To compare sirolimus levels measured in whole blood using two analytical techniques: high-resolution liquid chromatography and microparticle enzyme immunoassay, and to evaluate whether hemoglobin, hematocrit, and time from kidney transplantation influence results obtained using the immune-enzymatic technique.


METHOD
A retrospective, observational study in which all transplanted patients with at least one measurement of sirolimus levels using high-resolution liquid chromatography or microparticle enzyme immunoassay from October 2004 to May 2005 were consecutively included. For statistical comparisons simple linear regression, ANCOVA, intra-class correlation coefficient, and the method of agreement limits were all used.


RESULTS
Ninety-one patients were assessed for a total of 307 measurements (median: 2, inter-quartile range: 1-4, range: 1-15) of sirolimus levels. The straight-line equation using the linear regression analysis was as follows: MEIA = 0.70 (95% CI: 0.39-1.01) + 1.14 (95% CI: 1.10-1.17) x HPLC/UV. The intra-class correlation coefficient between both measurements was 0.955 (95% CI 0.944-0.964). Mean overestimation using enzyme immunoassay was 24.8% +/- 19.4%. Difference in means between both measurements was 1.9 +/- 1.3 ng/mL. Agreement limits were established between -0.8 ng/mL (95% CI: -1.05; -0.55) and +4.6 ng/mL (95% CI: 4.35; 4.85). Factors such as post-transplant time, hemoglobin, and hematocrit did not influence overestimates obtained using enzyme immunoassays. These results were not influenced by non-independence in measurements.


CONCLUSIONS
Despite enzyme immunoassay overestimates in establishing sirolimus levels in whole blood, its correlation with chromatography is acceptable. Added to its benefits versus chromatographic techniques, this renders enzyme immunoassay a good alternative for the measurement of sirolimus levels in whole blood.