Combinations of Anticyclic Citrullinated Protein Antibody, Rheumatoid Factor, and Serum Calprotectin Positivity Are Associated With the Diagnosis of Rheumatoid Arthritis Within 3 Years

Objective: To evaluate the prevalence of elevations of anti-cyclic citrullinated peptide-3 (anti-CCP3) antibody, rheumatoid factor IgM (RF-IgM) and serum calprotectin (sCP) in pre–rheumatoid arthritis (RA) as well as the diagnostic accuracies of these biomarkers for the timing of diagnosis of future RA. Methods: A total of 215 RA cases, each with approximately three pre-RA diagnoses and one post–RA diagnosis serum sample, and controls were identified from the Department of Defense Serum Repository. All case samples and a single sample from each control subject were tested for anti-CCP3 (IgG), RF-IgM, and sCP. The diagnostic accuracies of biomarkers for future RA were evaluated. Results: Anti-CCP3, RF-IgM, and sCP were elevated in pre-RA, with anti-CCP3 and sCP significantly elevated compared with RF-IgM at the earliest time points. Within the cases, the combination of anti-CCP3 and RF-IgM positivity had a positive predictive value (PPV) of 35.6% for a diagnosis of RA in 3 years or less, which is significantly higher than the PPV of 18.7% for anti-CCP3 positivity alone (P < 0.001). A combination of anti-CCP3, RF-IgM, and sCP had the highest PPV (53.0%) for a diagnosis of RA in 3 years or less; however, this was not significantly higher than the PPV for anti-CCP3 and RF-IgM positivity (P = 0.248). Conclusion: Anti-CCP3, RF-IgM, and sCP are elevated in pre-RA; furthermore, combinations of elevations of these biomarkers are more commonly seen in the period of less than or equal to 3 years to diagnosis. This may be considered in creating inclusion criteria in prevention trials in RA. In addition, the biologic relationships of these biomarkers in pre-RA need exploration.