YKL-40 Levels in Rheumatoid Arthritis and Their Correlation with Disease Activity: A Meta-analysis

Objective. To examine the relationship of serum/plasma YKL-40 levels with rheumatoid arthritis (RA) and their correlation with RA activity and rheumatoid factor (RF) level. Methods. We performed a meta-analysis comparing the serum/plasma YKL-40 levels between patients with RA and controls and examined the correlation coefficients of the circulating YKL-40 level with the RF level and RA activity based on the 28-joint disease activity score (DAS28), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) level. Results. Nine studies (707 patients with RA and 1,041 controls) were included in the meta-analysis. The YKL-40 levels were significantly higher in the RA group than in the control group (standardized mean difference [SMD]=1.071, 95% confidence interval [CI]=0.726∼1.417, p＜0.001). Stratification by ethnicity showed significantly elevated YKL-40 levels in the RA groups from European, Asian, North American, and Arab populations. The YKL-40 level was significantly higher in the RA group than in the control group in both age- and sex-matched and only age-matched populations (SMD=0.937, 95% CI=0.554∼1.320, p＜0.001; SMD=2.951, 95% CI=1.389∼4.512, p＜0.001, respectively). Subgroup analysis by sample size showed significantly increased YKL-40 levels in the RA group in both small (n＜100) and large (n＞100) populations. Meta-analysis of correlation coefficients showed a significant positive correlation between the YKL-40 levels and DAS28, ESR, CRP level, and RF level (DAS28: correlation coefficient=0.381, 95% CI=0.044∼0.640, p=0.028; RF level: correlation coefficient=0.341, 95% CI=0.176∼0.487, p＜0.001). Conclusion. The circulating YKL-40 levels are high in patients with RA and positively correlate with RA activity and RF level.