Predictive value of anti-citrullinated peptide antibodies: a real life experience

Rheumatoid Arthritis (RA) is an autoimmune destructive joint disease, characterized by the presence of rheumatoid factor and anti-citrullinated peptide antibodies. Anti-citrullinated peptide antibodies were recently defined as RA criterion with sensitivity and specificity of 50-80 and 75-95 %, respectively. However, in the general population, the predictive value of anti-citrullinated peptide antibodies is yet to be determined. Herein, we aim to determine the predictive value of anti-citrullinated peptide antibodies in real life as well as clinical and serological factors related to this value. Retrospective cross-sectional study of consecutive samples evaluated for anti-citrullinated peptide antibodies in a referral autoimmune laboratory. Demographic and clinical parameters at the time the sample was drawn were collected. During November 2011 through December 2013, a total of 215 anti-citrullinated peptide antibody tests were performed in our laboratory. Data were available for 140 samples of which only 28 samples were positive for anti-citrullinated peptide antibodies. Of the 140 patients tested, 18 were diagnosed with RA, of which 12 were positive and 6 were negative for anti-citrullinated peptide antibody test. Thus, in this cohort, anti-citrullinated peptide antibodies were positive in 20 % of samples with a positive predictive value (PPV) of 43 % and a negative predictive value of 95 %. In real life, only 20 % of anti-citrullinated peptide antibody tests referred to a tertiary center where found to be positive. The negative predictive value of this test is very high and may support the common use of anti-citrullinated peptide antibody test as an exclusion criterion in the process of evaluating a patient with rheumatic disease.