MRSPAH: a simple microtitre plate test for rheumatoid factors of different classes.

A simple and inexpensive microtitre plate test (the mixed reverse (solid-phase) passive antiglobulin haemadherence test, or MRSPAH) has been developed for the measurement of antiglobulins (RFS) of different classes. Results obtained for IgM RF by this test have been compared with results of latex and Rose-Waaler (DAT) tests on rheumatoid arthritis (RA) sera. Levels of RFs of IgM, IgG and IgA classes have been measured by MRSPAH using rabbit IgG as antigen in RAs and normal people. 94% of RA sera tested were above the upper limit of normal for IgM and/or IgA RF. There was a considerable overlap between IgG RF levels in RAs and normals, although the means of the two groups were significantly different.