Fasting is a situation in which the stomach contents enter the intestine and there is no food in the stomach. However, different situations will have different fasting time requirements and should be looked at on a case-by-case basis. In reality, we often encounter fasting problems such as fasting for laboratory tests, fasting for medications, fasting for food restrictions, etc. The requirement of taking medicine on an empty stomach mainly refers to 0.5-1 hour before meals, which is mainly to be more conducive to the absorption of the active ingredients of drugs. For the usual said should not eat certain foods on an empty stomach when fasting mainly refers to before meals, basically equivalent to 3-4 hours after meals. In general, blood tests, abdominal imaging (ultrasound, CT, MRI), etc. require fasting for more than 8 hours, i.e., no food, including water and beverages, should be consumed after 12:00 pm the night before the test. The main reason for fasting is to avoid or reduce the effect of diet on the examination items. Moreover, not all blood tests require fasting. For routine blood tests, blood clotting, tumor markers, etc., whether or not fasting has little effect on the test results.