Superior specificity of anti-citrullinated peptide antibodies in patients with chronic lymphocytic leukaemia and arthritis

Objective. Sera front patients with lymphoid neoplasias contain rheumatoid factors (RF) so often that RF are of limited use for diagnosing arthritis in lymphoma patients. Antibodies against citrullinated peptides (ACPA) might be helpfill in distinguishing between true RA and rheumatoid factor-positive conditions with arthritis. We compared the specificity of RF and of ACPA for the diagnosis of RA in patients with B-cell chronic lymphocytic leukemia (CLL). Methods. One hundred and seven patients with CLL without any clinical signs of arthritis and five patients with RA and concomitant CLL were included in the investigation. Serum samples were tested for RF-isotypes IgM, IgG and IgA. ACPA were determined with an ELISA that detects anti-cyclic citrullinated peptide (aCCP) antibodies. Results. RF well beyond the cut-off levels were detected in 50% of the CLL-patients without RA. The isotype distribution was 41% IgM-RF, 20% IgG-RF and 3% IgA-RF. None of the 107 CLL patients without arthritis had aCCP antibodies. Within the whole cohort of CLL patients the specificity for the diagnosis of RA was 100% for aCCP antibodies and 59% for IgM-RF. Conclusion. Only aCCP antibodies hut not IgM-, IgG- or IgA-RF are useful for the diagnosis of RA in patients with CLL.