Performance characteristics of the PolyTiter Immunofluorescent Titration system for determination of antinuclear antibody endpoint dilution.

Conventional screening for circulating antinuclear antibodies (ANA) is generally performed by immunofluorescent (IF) microscopy with a 1:40 dilution of serum. Intensity of IF staining is then semiquantitated by using twofold serial dilutions, where the highest dilution in which staining intensity equals the endpoint control is expressed as an endpoint titer. The PolyTiter Immunofluorescent Titration system (Polymedco, Inc.) facilitates ANA-IF assay (IFA) testing by relating the intensity of IF staining to reference calibrators (defined in PolyTiter units), providing an endpoint titer directly from a 1:40 dilution. This study was conducted to assess the performance characteristics of the PolyTiter system. Two technologists each evaluated 10 replicates of three specimens and two controls on five sequential days. Endpoint dilution agreement (defined as +/-2 dilutions) with the reference was 100% for all controls and for all specimens by one technologist. The second reader reported agreement of 98, 88, and 100% for the low, medium, and high specimens, respectively. Analysis of PolyTiter unit values yielded between-reader, between-run, and within-run precision coefficients of variation of less than 10%. The variance component in the lot-to-lot analysis was zero, indicating all of the variation was due to run-to-run differences. Overall endpoint dilution agreement between PolyTiter and serial dilution in the evaluation of 125 specimens at three sites was 90, 93, and 86%. Pattern identification with the PolyTiter was similar to that with serial dilution. The PolyTiter system demonstrates acceptable performance for routine ANA-IFA testing in the clinical laboratory.