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.