The presence of antinuclear antibody in serum has been used to serologically support the clinical diagnosis of systemic lupus erythematosus. Most often, diagnostic support is conferred if the titer is above a "cut-off" value determined by the particular laboratory. The precision estimates of these commonly used serological assays are high. The arithmetic and geometric precisions estimates of fluorescent antinuclear antibody (FANA) assays were determined utilizing sera from dogs with polysystemic signalment suggestive of SLE. A simple score assay was found to have improved precision over FANA endpoint titrations on Hep-2 or cryostat, rat liver substrates. In one case, the precision improved from an arithmetic coefficient of variation of 25.6% (HEp-2, endpoint dilution, FANA titers) or 19.7% (rat liver cryostat substrate FANA titers) to 15.5%. Geometric coefficients of variation followed similar trends. Further, the score values for dogs with SLE were considerably higher (mean = 3.28) than for clinically normal dogs (mean = 0.20). The score system was more precise than FANA endpoint titers and therefore may be useful for diagnostic purposes, especially when FANA titers are negative or low.
Animals Antibodies, Antinuclear