IMPROVED IMMUNOTURBIDIMETRIC METHOD FOR RHEUMATOID-FACTOR TESTING

The performance of two immunoturbidimetric modifications for rheumatoi d factor (RF) testing, which differ with respect to the means of compl ement inactivation (heat treatment and inactivation with polyvinyl sul phonate), were compared in serum samples from 87 patients with rheumat oid arthritis (RA) and from 403 healthy subjects. IgM-rheumatoid facto r titres were also measured with an enzyme linked immunosorbent assay (ELISA). Both immunoturbidimetric tests gave positive reactions (rheum atoid factor greater-than-or-equal-to 20 IU/ml) in 74 out of the 87 (8 5%) RA sera. In cases with high RF concentrations the results after ch emical inactivation tended to be slightly higher compared with heat in activation. In healthy subjects rheumatoid factor was detected in 19/4 03 (4.7%) sera using heat inactivation and in 22/403 (5.5%) sera with chemical inactivation of complement. Interrun coefficient of variation in the chemical inactivation assay was 4.4%; with the heat inactivati on method it was 8.1%. In the ELISA, a marginally better correlation w as noted in the results obtained using chemical inactivation. Inactiva tion of complement by means of polyvinyl sulphonate offers the advanta ge of easier test performance and better reproducibility, and the resu lts may reflect more accurately true rheumatoid