The seven items of trace elements that patients generally go to the hospital for are not an exact fixed category of tests, and there are different kinds of distinctions for different hospitals. General trace elements refer to copper, cobalt, iron, zinc, selenium, manganese, iodine, silicon, fluorine, molybdenum and other 18 elements, accounting for less than 0.01% of body weight. In addition, although magnesium and calcium account for a high proportion of the body belongs to the macronutrients, but because the free part is less, also belong to trace elements. The seven elements are calcium, magnesium, copper, lead, iodine, iron and zinc. Calcium ions are involved in a variety of biochemical reactions in the body, including blood clotting, cardiac muscle contraction, osteoblasts and osteoclasts, and maintaining the stability of the nervous system. Iron is an important raw material for the synthesis of hemoglobin. Iron deficiency leads to insufficient synthesis of hemoglobin, resulting in small cell anemia. The seven tests for trace elements are not fixed tests and different hospitals have different types.