Detection of anti-cyclic citrullinated peptide antibodies (ACPA) was performed with automatic multiplex method for anti-CCP2 antibodies (BioPlex® 2,200 System, BioRad, Hercules, CA, USA). The levels of ACPA in each sample were quantified against the calibration curve. The cut-off level above 20 AU/ml was regarded positive. This corresponded to the mean+2SD of the healthy control group. Total RF, antibodies against Fc-region of gamma globulin, was measured by nephelometry (Beckman Immage 800, Beckman Coulter AB, Brea, CA, USA). The levels of total RF were presented in U/ml. The cut-off for RF positivity was 20 U/ml. The measurements of ACPA and RF were performed at the accredited laboratory of Clinical Immunology, Sahlgrenska University Hospital.
Serum levels of CRP were measured at the Laboratory of Clinical Chemistry, Sahlgrenska University Hospital, by nephelomety (Beckman Immage 800). The cut-off level for positivity was 5 mg/L.
Serum levels of survivin were measured in samples diluted 1:10 using a sandwich enzyme-linked immunoassay comprising a pair of matched antibodies and recombinant standard (DY647, R&D Systems, Minneapolis, MN USA); the detection limit was 100 pg/ml. The cut-off level for survivin positivity was set to 450 pg/ml corresponding to the mean+3SD of 104 healthy individuals (39 (link)).
Serum levels of CRP were measured at the Laboratory of Clinical Chemistry, Sahlgrenska University Hospital, by nephelomety (Beckman Immage 800). The cut-off level for positivity was 5 mg/L.
Serum levels of survivin were measured in samples diluted 1:10 using a sandwich enzyme-linked immunoassay comprising a pair of matched antibodies and recombinant standard (DY647, R&D Systems, Minneapolis, MN USA); the detection limit was 100 pg/ml. The cut-off level for survivin positivity was set to 450 pg/ml corresponding to the mean+3SD of 104 healthy individuals (39 (link)).