Fasting blood glucose is usually fasted for 8 to 10 hours prior to the measurement of fasting blood glucose, and the test is used for screening for diabetes and other diseases. Normally, 8 to 10 hours of fasting is required before performing a fasting blood glucose test, which is often performed clinically in the early morning of the next day after a night of fasting. The test is the most commonly used and important indicator for diagnosing disorders of glucose metabolism. Its normal value is 3.9~6.1mmol/L, which may vary from laboratory to laboratory. Physiological factors such as strenuous exercise and emotional excitement prior to the measurement, as well as pathologic factors such as diabetes and hyperthyroidism, can lead to an increase in this indicator. Physiological factors such as prolonged starvation, prolonged strenuous exercise, pathological factors such as pancreatic β-cell hyperplasia or tumors, acute severe hepatitis, hypoadrenocorticism, hypothyroidism, etc. can lead to a decrease in the index. Abnormalities of this indicator are recommended to go to the hospital in time.