The presence of IgM class rheumatoid factor RF-M in the serum is one of the ACR criteria for the classification of rheumatoid arthritis RA .
To compare the sensitivity and specificity of two diagnostic markers for RA in Portuguese patients the 2nd generation anti-cyclic citrullinated peptide antibodies anti-CCP2 and the RF-M.
Serum samples from 56 patients with established RA 44 women and 12 men mean disease duration 9 5 -8 5 years were evaluated for the presence of anti-CCP2 and RF-M. Results were compared with 93 samples from a control group with identical demographic characteristics 43 from patients with spondylarthropaties and 50 from healthy blood donors . The determination of anti-CCP2 antibodies was performed by enzymatic fluroimunoassay and RF-M was measured by microElisa.
Anti-CCP2 antibodies were positive in 40 patients with RA 71 4 at a mean antibody concentration of 350 5 UA ml range 11-1670 UA ml and negative in all controls. The RF-M was positive in 34 patients with RA 60 7 in 4 patients with spondylarthropaties 9 3 and in one blood donor 2 . The sensitivity specificity positive predictive value and negative predictive value for RF-M was 60 7 90 7 89 5 and 63 9 and for anti-CCP2 was 71 4 100 100 and 72 9 respectively.
The anti-CCP2 assay showed an excellent specificity and a global performance superior to that of the RF-M test in this population with established RA.