This study is designed to compare the serum sphingolipidomic analyses in healthy, pre-diabetic and diabetic subjects. age, sex and BMI are matched among these three groups. As ceramide, sphingosine, sphingosine-1-phosphate and sphinganine are involved in inflammation, immunity and cancer, investigators proposed a hypothesis that sphingosine-1-phosphate and other sphingolipids may be associated with the progress of type 2 diabetes. sphingolipids may be a biomarker for diabetes.