Comparison of Plasma Concentration of Linezolid's Detection by FICA and LC-MS/MS

Linezolid was the first totally synthetic oxazolidinone antibiotic that was approved for clinical use against Mycobacterium tuberculosis. Our study investigated the correlation and consistency of fluorescence immunochromatography assay (FICA) and high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) in measuring linezolid levels in the plasma. Plasma samples were collected from 80 to 100 tuberculosis patients. The samples were analyzed by FICA and LC-MS/MS, and linezolid levels measured by the two methods were compared by outlier test, correlation coefficient, Bland-Altman scatter plot, Deming regression analysis and bias evaluation. A total of 83 plasma samples were collected, all of which were non-outlier. The correlation coefficient of FICA and LC-MS/MS results was 0.9845. Deming regression analysis showed that the regression equation of FICA and LC-MS/MS was y = 0.2229 + 1.0076x. The medical decision levels of 2 and 7 μg/mL were taken into the regression equation, and the 95% CI of 2- and 7-μg/mL bias were both within the allowed error range. The findings indicated a strong correlation between the results obtained from FICA and LC-MS/MS were consistent showed good correlation, demonstrating their equivalence in measurement.