Objectives We measured serum levels of soluble intercellular adhesion molecule-1 (sICAM-1) and erythrocyte membrane Na+, K+, ATPase activity and the correlation of these parameters in patients with rheumatoid arthritis (RA), and investigated whether the levels of sICAM-1 were correlated with the disease activity.

Methods Serum sICAM-1 levels were determined with sandwich enzyme-linked immunosorbent assay (ELISA) and erythrocyte membrane Na+, K+, ATPase activity with spectrophotometric method in sera from 42 patients with RA and in 30 healthy controls. Eryhtrocyte sedimentation rate (ESR) was determined according to the Westergren method and C-reactive protein (CRP) by nephelometric method. Disease activity was assessed by disease activity criterias.

Results Although decreased erythrocyte membrane Na+, K+, ATPase activity, serum levels of sICAM-1 were significantly higher in patients with RA than in healthy controls. Significant negative correlations between sICAM-1 levels and erythrocyte membrane Na+, K+, ATPase activity (r = -0.678, p < 0.001) were observed. There was a weak but statistically significant positive correlation between sICAM-1 levels with Ritchie articular index (RAI) score and CRP (r = 0.32, p < 0.05; r = 0.44, p < 0.01, respectively), whereas no significant correlation was observed between sICAM-1 levels with ESR, age and disease duration. There was no correlation between values of CRP, RAI and ESR with erythrocyte membrane Na+, K+, ATPase activity.

Conclusion From these data, it is concluded that the decreases in erythrocyte membrane Na+, K+, ATPase activity and increases in sICAM-1, ESR and CRP levels are present in RA, and that the decrease in erythrocyte membrane Na+, K+, ATPase activity in RA might be due to increased sICAM-1, and increased levels of sICAM-1 and correlations with other parameters may be a significant and novel marker for evaluating the disease status and the activity of RA.