Comparison of ANA endpoint dilution using the PolyTiter immunofluorescent titration system and conventional serial dilution

The PolyTiter immunofluorescent titration system (PolyTiter system), an attachment for conventional fluorescent microscopes, facilitates immunofluorescent antinuclear antibody (IFA-ANA) testing by using calibrated light attenuation to determine the semiquantitative endpoint dilution or titer of ANA-positive specimens. The objective of this study was to compare the determination of ANA titer using the PolyTiter system to that of the conventional serial dilution method. A total of 172 consecutive ANA-IFA positive serum specimens, including the four most common pattern types, were evaluated in parallel by two readers to determine the dilution endpoint. The two methods produced equal dilution endpoints in 78 specimens (45%), within 1-dilution endpoint in 121 specimens (70%), and within 2-dilutions endpoint in 158 specimens (92%). The conventional method consistently produced a more conservative dilution endpoint than the PolyTiter system for three of the four patterns evaluated (i.e., centromere, nucleolar, and speckled vs. homogeneous). The PolyTiter system demonstrated satisfactory performance in comparison to the current standard for determining ANA dilution endpoints, while significantly reducing operator labor, time, and materials usage.