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BACKGROUND-AIM. Vancomycin is a tricyclic glycopeptide with bacteriocidal activity against several strains of gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Our aim was to verify the Beckman Coulter EMIT 2000Vancomycin Assay (Enzyme Multiplied Immunoassay Technique, EMIT) for routine vancomycin determination on theBeckman Coulter AU680 automatic analyzer (Beckman Coulter, Brea, USA).METHODS. The verification was performed according to CLSI EP15- A2 protocol. Precision was examined using two levels ofcommercial control samples (Bio-Rad Laboratories, Hercules, USA). Obtained coefficients of variation (CVs) were interpreted according to manufacturer’s criteria for total laboratory precision (3, 8% for L1 and 2, 5% for L2). Truenesswas assessed by a comparison experiment, by analyzing 20 patient samples and comparing the resuls with the Abbott Architect assay (Chemiluminescent Magnetic Microparticle Immunoassay, CMIA), accredited according to the ISO15189 norm. The results were statistically processed in the MedCalc program (v.17.9.2) by Passing-Bablok regressionanalysis.RESULTS. The obtained CVs for total laboratory precision were 2, 4% (L1, target value 4, 49 μmol/L) and 1, 7% (L2, target value18, 90 μmol/L). Passing-Bablok analysis yields the regression line y = 0, 39 (95% CI: 0, 15-0, 78) + 0, 74x (95% CI:0, 69-0, 77) which indicates the presence of both constant and proportional bias. Therapeutic ranges recommended bythe reagent manufacturer differ between the two compared methods. If the classification of samples is compared byboth methods, 18/20 samples are classified in the same way (below, within or above the therapeutic range), whichindicates satisfactory agreement between the methods.CONCLUSIONSThe evaluated method meets the manufacturer's criteria for total laboratory precision. Method comparison analysis with the previously used method indicates the presence of both constant and proportional error, but given that themethods classify 90% of samples equally using their own therapeutic ranges, substitution of the methods is possible if therapeutic ranges are changed. Therefore, the Beckman Coulter EMIT 2000 Vancomycin Assay is considered as an acceptable method for routine vancomycin therapeutic drug monitoring. |
