Do I need to fast for a blood test? Generally speaking, many indicators of the body are different before and after meals, such as liver function, bilirubin, transaminases, and blood sugar, especially blood sugar, which is particularly susceptible to pre- and post-meal effects. Therefore, it is required to fast during the physical examination, especially during the blood test, to measure the specific values. In the routine physical examination, when the liver and kidney function, you can eat and drink a little water after the blood is drawn. If you haven’t eaten breakfast, you can eat a little breakfast with relatively low sugar content.