Previous studies showed that angiopoietin-1(Ang-1) expression was increased in the synovium in early rheumatoid arthritis (RA) patients. The present study was therefore designed to examine whether determination of serum Ang-1 might be effective in diagnosis of early RA.
One hundred and five serum samples of RA (21 males, 84 females) were studied for serum Ang-1 level. Serum samples were also collected from other collagen diseases, including 35 cases of SLE, 29 cases of systemic sclerosis, 16 cases of polymyositis/dermatomyositis. Serum samples were additionally obtained from 34 patients who visited our clinic for evaluation of symmetrical polyarthritis with morning stiffness. After one year of follow-up, those patients who satisfied the ACR 1987 classification criteria for RA were defined as 'early RA'. Serum Ang-1 levels were measured by sandwich ELISA using anti-angiopoietin-1 antibodies (both monoclonal and polyclonal antibodies). Serum anti-CCP antibody and rheumatoid factor (RF) were measured by ELISA and by laser nepherometry, respectively.
Serum Ang-1 in RA patients was significantly higher than those in other collagen diseases. Serum Ang-1 levels in 50 normal healthy individuals were 5.8 ± 0.31 pg/ml (mean ± SEM). There was no significant difference in CRP and serum RF at the first visit between early RA patients and non-RA patients, whereas serum Ang-1 levels at the first visit were significantly higher in early RA (58.7 ± 17.9 pg/ml [mean ± SEM]) than those in non-RA (8.2 ± 4.5 pg/ml). ROC analysis revealed that serum Ang-1 (cut-off 23.91 pg/ml) could diagnose early RA at sensitivity 57.1% and specificity 84.6%, providing comparable area under the curve (0.71, 95% CI: 0.54-0.88) to that of serum anti-CCP antibody (0.72, 95% CI: 0.53-0.92). There was no significant correlation between anti-CCP antibody and Ang-1.
These results indicate that serum Ang-1 is as useful a marker for the diagnosis of early RA as serum anti-CCP antibody.