RESUMO
BACKGROUND: Correlation of the assay cut-off values for CaptiaTM Measles IgG and the Vidas® Measles IgG assays with the World Health Organization recommended immunoprotective level of ≥120â¯mIU/mL is not stated by the manufacturers. Lack of such information may affect interpretation of immune protection (IP) for measles. OBJECTIVE: The aim of this study was to compare the relative performance of the CaptiaTM Measles IgG assay and the Vidas® Measles IgG assay for determination of IP against measles virus. STUDY DESIGN: Correlation of the cut-off value of both assays with the immunoprotective level was determined with the 3rd WHO Measles IgG International Standard. One hundred clinical samples including frozen and fresh were tested with both assays. The positive percentage agreement (PPA) based on the manufacturers' interpretation and the WHO recommended immunoprotective level was compared. RESULTS: Samples tested positive by the CaptiaTM assay were at or above the immunoprotective level while those tested equivocal and positive by the Vidas® assay were immune protective. The overall PPA between both assays was 78.31 % (95 % CI = 67.91-86.61%). When Vidas® equivocal results were regarded as immunoprotective, the overall IP agreement was 96.39 % (95 % CI = 89.80-99.25 %). CONCLUSIONS: CaptiaTM assay was more sensitive than the Vidas® assay in determination of IP against measles virus. Testing of measles immunity with the Vidas® Measles IgG assay might underestimate the IP unless equivocal results were regarded as immunoprotective.