Combined elevation of IgM and IgA rheumatoid factor has high diagnostic specificity for rheumatoid arthritis

Rheumatol Int. 1998;18(3):119-22. doi: 10.1007/s002960050069.


The diagnostic value of measuring rheumatoid factor (RF) by agglutination or isotype-specific enzyme-linked immunosorbent assay (ELISA) was compared. The study included 70 patients with rheumatoid arthritis (RA) and 205 patients with various other rheumatic conditions. Of the RA patients, 74% were RF-positive by agglutination and 90% had one or more RF isotypes elevated by ELISA compared to 14% and 22%, respectively, of the other patients. Strikingly, 70% of the RF-positive RA patients had an elevation of two or more RF isotypes compared to only 16% of the other RF-positive patients (P < 0.0001). Furthermore, a combined elevation of IgM and IgA RF was found in 52% of the RF-positive RA patients, but only in two (4%) of the other RF-positive patients (P < 0.0001). It is concluded that a combined elevation of IgM and IgA RF is highly specific for RA and is very rarely found in rheumatic diseases other than RA. Isotype-specific RF assays are therefore diagnostically superior to agglutination tests. The detection of the RA-specific RF isotype pattern may be particularly helpful early in the course of RA even before the disease is fully differentiated.

Publication types

  • Comparative Study

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Agglutination Tests
  • Arthritis, Rheumatoid / diagnosis*
  • Arthritis, Rheumatoid / immunology*
  • Enzyme-Linked Immunosorbent Assay
  • Female
  • Humans
  • Immunoglobulin A / analysis*
  • Immunoglobulin M / analysis*
  • Male
  • Middle Aged
  • Rheumatoid Factor / analysis*
  • Sensitivity and Specificity


  • Immunoglobulin A
  • Immunoglobulin M
  • Rheumatoid Factor