Dear Editor,The publication on “Leptin as an independent marker of metabolic syndrome” by Tseng et al. is very interesting [1]. Tseng et al. concluded that “Serum leptin is positively correlated with MetS. It serves as an independent marker of MetS in elderly patients with T2DM [1].” In fact, the usefulness of serum leptin is widely mentioned. Nevertheless, there are many possible confounding factors that might disturb the determination. First, exercise can result in lowering leptin level [2]. Second, in the case with underlying liver problem and abnormal elevated bilirubin level (such as in cases with chronic hepatitis), the interference on leptin level measurement is possible [3]. Hence, the patients with underlying hepatitis should be excluded from the study. These factors have to be concerned in the study by Tseng et al. [1].