The regression analysis results showed that self-injury frequency (a psychological indicator) in the past month (odds ratio [OR]: 1.588, 95% confidence interval [CI]: 1.006–2.508, P = 0.047) and serum CRP level (a biochemical indicator) were predictors of suicidal behavior in the participants having MDD with NSSI (OR: 0.392, 95% CI: 0.200–0.767, P = 0.006; Supplementary Table 1). This evidence concerns the gene CRP and major depressive disorder.