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> &lt; 0.001) and CRP (r = 0.243, <i>p</i> &lt; 0.001). C4 levels also correlated with ESR (r = 0.175, <i>p</i> = 0.001) and CRP (r = 0.263, <i>p</i> &lt; 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. Association of serum complement levels with clinical characteristics This study found a positive correlation between serum complements (C3 and C4) and OA patients' clinical characteristics and inflammatory activity indicators. Proposed tool for predicting OA activity The study proposes a convenient tool for predicting OA activity based on C3 and C4 levels. Clinical characteristics of patients with abnormal complement levels Changes related to complements and inflammatory markers such as ESR and CRP may play an essential role in the pathogenesis of AC-OA (comparison of clinical characteristics of OA patients with abnormal complement levels). Correlation between serum complements and disease activity indicators Complement levels are positively correlated with disease activity indicators of OA such as ESR and CRP (correlation between serum complements and disease activity indicators in OA patients). Association of C4 levels with the number of affected joints Lower C4 levels are more strongly associated with fewer affected joints (correlation between serum complement levels and the number of affected joints in OA patients). Types of joints affected by OA There is no significant association between C4 levels and the types of joints affected in OA patients (Correlation between serum complement levels and types of affected joints in OA patients). Effect of confounding factors on ESR Levels After excluding confounding factors, the significance of the correlation between C3 and C4 levels and ESR levels is reduced (Correlation between serum complement levels and ESR levels in OA patients). Association between C4 and CRP Levels C4 levels positively correlate with CRP levels (correlation between serum complement levels and CRP levels in OA patients).