APLN and coronary artery disorder: In overall analysis, circulating apelin concentration was significantly lower in CAD patients than in controls (WMD: -1.285 ng/mL, 95% CI: -1.790 to -0.780, P < 0001), while statistical heterogeneity was significant (I2: 99.3%, P < 0.001) (Figure 1: the UPPER panel).