Association Between Circulating Levels of C1q/TNF-Related Protein-9 and Type 2 Diabetes Mellitus: A Systematic Review and Meta-analysis

Context According to growing research, C1q/TNF-Related Protein-9 (CTRP9) appears to be linked to type 2 diabetes mellitus (T2DM). But the literature on circulating levels of CTRP9 in patients with T2DM has been contradictory. Objective This is a systematic review and meta-analysis to reassess the circulating level of CTRP9 in patients with T2DM, with and without complications. Methods Relevant studies published until October 31, 2021, were identified from the PubMed, Embase, Web of Science, Cochrane Library, WanFang, CNKI, VIP, and CBM databases. Participants with age >= 18 years with clinically diagnosed T2DM were included. Sex and diabetes complications were not restricted. The data were extracted by 2 reviewers independently using a standard data collection form. Results Analysis demonstrated significantly lower circulating levels of CTRP9 in patients with T2DM than in patients without diabetes (standardized mean difference [SMD] = -1.36; 95% CI -1.78 to -0.93; P < .001), I-2 = 97.5%, P < .001). Furthermore, the circulating level of CTRP9 in patients with T2DM-related complications was lower than that in patients with T2DM without complications, regardless of macrovascular complications or microvascular complications (SMD = -1.062; 95% CI -1.466 to -0.658; P < .001, I-2 = 91.3%, P < .001). Subgroup analyses revealed that factors such as body mass index, T2DM duration, and fasting blood glucose were the sources of heterogeneity (P = .047, P = .034, and P = .07, respectively). Conclusion The present systematic review and meta-analysis found CTRP9 levels were lower in T2DM patients with or without complications. However, since this was a meta-analysis of most observational studies, these findings still need to be verified by further studies with a large sample size.