LEP and hepatocellular carcinoma: Stratification by Alanine aminotransferase (ALT) levels of HCC patients showed HCC group had significantly higher leptin levels than CFC group in “< 70 U/L” (SMD = 4.42, 95% CI (2.26, 6.50), P = 0.000), but not in the “≥ 70 U/L” (SMD = 0.43, 95% CI (− 0.38, 1.23), P = 0.296).