Stratification by study design showed HCC group had significantly higher AdipoQ levels than CFC group in nested case-control studies (SMD = 0.25, 95% CI (0.14, 0.36), P = 0.000), but not in case-control studies (SMD = 0.84, 95% CI (− 0.74, 2.12), P = 0.298), and cross-sectional studies (SMD = − 1.10, 95% CI (− 3.46, 1.26), P = 0.361). The gene discussed is ADIPOQ; the disease is hepatocellular carcinoma.