Circulating CTRP1 in Adults with Type 2 Diabetes Mellitus: A Systematic Review and Meta-Analysis.

Type 2 diabetes mellitus (T2DM) is typically associated with a dysregulated adipokine profile. C1q tumour necrosis factor-related protein 1 (CTRP1) is a relatively novel adipokine with protective metabolic effects, including improved insulin sensitivity. Clinical studies have increasingly highlighted a potential association between circulating CTRP1 and T2DM. Therefore, this systematic review and meta-analysis aimed to synthesise existing data on the association between circulating CTRP1 concentrations and T2DM in adults. MEDLINE, EMBASE, Cochrane Library, Web of Science, CINAHL and PsycInfo databases were searched for studies measuring circulating CTRP1 in adults with T2DM and controls. Eligible data were meta-analysed, reporting the mean difference (MD) and 95% confidence intervals (CIs) of circulating CTRP1 concentrations between T2DM cases and controls. The Revised Risk of Bias Assessment Tool for Nonrandomized Studies of Interventions (RoBANS 2) and the National Institutes of Health (NIH) quality assessment tool were utilised for study risk of bias and quality assessments, respectively. Eight studies (525 T2DM cases; 612 non-T2DM controls) were eligible for meta-analysis, showing significantly higher circulating CTRP1 concentrations in T2DM cases than controls (MD: 185.31 ng/mL; 95% CI: 140.02 to 230.60; p < 0.001). Most included studies were cross-sectional, and considerable heterogeneity was noted, with five studies having a high risk of bias in at least one RoBANS 2 domain. The MD remained relatively unchanged following a leave-one-out sensitivity analysis and exclusion of poor-quality studies. Meta-regression indicated that studies with a greater proportion of males (β = -188.68, p = 0.01) and higher mean body mass index (β = -23.96, p = 0.02) were associated with a lower MD. These findings indicate that circulating CTRP1 concentrations are significantly higher in adults with T2DM compared to non-T2DM controls. Future prospective and large-scale studies are required to delineate the nature of this association and explore the potential of CTRP1 as a biomarker for T2DM. PROSPERO registration ID: CRD420251137104.