Complement 3 and 4 impact in osteoarthritis

<b>Aim:</b> To investigate the association between serum complement 3 and 4 (C3 and C4) levels and clinical characteristics in osteoarthritis (OA) patients.<b>Methods:</b> This retrospective study included 361 OA patients divided into groups based on complement levels. Clinical data and laboratory test results, including C3, C4, ESR and CRP levels, were analyzed using non-parametric tests, Spearman correlation and multivariate regression.<b>Results:</b> The AC-OA group had lower PA, C3, C4, ESR, CRP and IgA levels compared with controls. C3 levels were positively correlated with ESR (r = 0.260, <i>p</i> < 0.001) and CRP (r = 0.243, <i>p</i> < 0.001). C4 levels also correlated with ESR (r = 0.175, <i>p</i> = 0.001) and CRP (r = 0.263, <i>p</i> < 0.001) and were significantly associated with the number of affected joints.<b>Conclusion:</b> Serum C4 levels are effective indicators of disease activity in OA, particularly in terms of joint involvement and CRP levels, while C3 levels showed no significant association. These findings suggest a potential role for C4 in predicting OA activity.