Check whether white blood cells need to fasting is mainly divided into the following cases, as follows: 1, check the blood routine, urine routine: are not strictly fasting, do urine routine testing, although you can eat, drink water, but if the symptoms and the need to go to check; 2, blood biochemical examination: need to fasting, because after eating will have an impact on blood sugar, liver enzymes, fasting can reduce such artificial interference, so when doing biochemical examination is recommended 3, urine sugar test: after eating, blood sugar increases, urine sugar is positive, so you need to keep fasting; 4, serious urinary tract infection: urine white blood cells are elevated, at this time, whether to drink water, eat, are not affected. However, if the infection is milder, it is recommended that patients take morning urine, relatively at night or in the morning without eating or drinking. At this time, the urine is more concentrated and it is easier to detect mild leukocyte elevations. If you drink water, there will be a degree of dilution of white blood cells in the urine and minor infections may be missed.