[Nationwide survey for autoantibodies and proposal of a new method for standardization of rheumatoid factors].

There exist inter-laboratory differences in measurements of rheumatoid factor (RF) and antinuclear antibodies (ANA), leading to a misdiagnosis of rheumatoid arthritis (RA) and other collagen diseases. This study was carried out to bring the positivity of RF and ANA of different reagents into accord by standardizing their data. The titer and cutoff value was inconsistent among the 17 different kits. We found a possibility in standardization of RF by a new concept in cooperation with Japanese Committee for Clinical Laboratory Standards (JCCLS). Sera from 1300 healthy subjects and 79 RA patients were measured for RF by 17 different RF kits, and sera with a little deviation among the kits were selected. Panels for detection of RF positive rate in healthy subjects were made from the pooled sera. The cutoff value in 5% positive in the panel was defined tentatively as 15 IU/ml. The 100 IU/ml was also able to become in general accord by adjusting the individual data using pooled RF-positive reference sera. The nationwide survey of immunofluorescence ANA (IF-ANA) was performed in 41 laboratories using 6 pooled sera. The reported titer was fairly different among laboratories, and a striking discrepancy was found for low-titer samples. When the titer was corrected by simultaneously measured reference serum, inconsistency of ANA titer among different laboratories was mostly compensated. Here, we propose a new method for standardization of RF and also try to standardize the positivity of RF and IF-ANA by providing pooled reference sera.