Chen H, Zhang J, Lai J, et al. - Low-quality evidence was found that in comparison with controls, patients with coronary artery disease (CAD) exhibited similar circulating Retinol binding protein 4 (RBP4) levels, and high inter-study heterogeneity was also observed. Therefore, for CAD, RBP4 might not be a potential risk factor. There is a need for comparisons among different subtypes of RBP4 with a larger sample size in the future.

• Researchers conducted two nested case-control studies, one cohort study, and twelve case-control studies including a total of 7,111 participants.

• In patients with CAD, circulating RBP4 levels were comparable to those in the controls under the IVhet model ([standard mean difference (SMD)]: 0.25, 95% CI: − 0.29-0.79, I2: 96.00%).

• Furthermore, the quality-effects model produced consistent outcomes.

• Nevertheless, the relationship turned to be significant under the random-effect model (SMD: 0.46, 95% CI: 0.17–0.75, I2: 96.00%), whereas the 95% prediction interval (PI) included null values (95% PI: − 0.82-1.74).

• In the subgroup analyses, data demonstrated a positive association between CAD and RBP4 levels in patients with complications (SMD: 1.34, 95% CI: 0.38–2.29, I2: 96.00%).

• In addition, the meta-regression analysis indicated that the mean BMI of patients (P = 0.03) and complication status (P = 0.01) influenced the variation in SMD.