Characterizing Synovial Fluid in Anti-CCP-Positive and Negative RA Patients

SF samples were obtained during knee joint aspiration from 10 anti-CCP-negative (median anti-CCP: 3.6 U/ml [interquartile range: 2–11.4 U/ml]) and 32 anti-CCP-positive (878 U/ml; [136–1353] U/ml) RA patients fulfilling the American College of Rheumatology criteria [38 (link)] and characterised with respect to disease-activity, as assessed by DAS28. The majority of the SF samples were also used in a recent study [12 (link)]. All SF samples were centrifuged at 1900 g for 10 min to remove cells and debris and stored at -80°C until use. Plasma from all patients but four was isolated from peripheral venous blood from the same patients at the time of arthrocentesis. The study was approved by the local ethics committee of the Institute of Rheumatology in Prague (No. 3294/2012), Czech Republic, and written informed consent was obtained from all patients.
Serum anti-CCP antibodies and IgM-rheumatoid factor were determined by standard ELISA kits (TestLine Clinical Diagnostics, Brunn, Czech Republic). Serum CRP was measured using an immuno-turbidimetric technique with an Olympus biochemical analyser, model AU 400 (Olympus, Tokyo, Japan) and SF leukocytes were counted using the Iris IQ200 (Beckman Coulter, CA, USA) analyzer.