Trace element tests for 12 year old children require fasting. Trace element tests are routine tests performed in the laboratory to examine the major trace elements such as calcium, iron, zinc, copper, magnesium and lead during the formative years of children. Fasting is required to ensure the accuracy of the test and to avoid abnormal effects of food on the test results. Although trace elements are not abundant in the body, they are essential to the growth and development of children and are of great significance to their growth and development. A deficiency of iron in trace elements can easily form iron deficiency anemia, which can lead to malnutrition and pallor. If there is a deficiency of zinc in trace elements, there will be obvious loss of appetite, paranoia, picky eating, etc. If there is a deficiency of calcium in trace elements, there will be growing pains and changes in the nervous system, such as difficulty sleeping or night sweats after sleeping, etc. Therefore, in order to ensure the accuracy of the test, it is necessary to perform the trace element test on an empty stomach.