Generally, there will not be any sudden loss of weight or significant change in weight after blood donation. If there is sudden loss of weight after blood donation, it is necessary to go to the hospital for a clear diagnosis of dyspepsia, hyperthyroidism, tumor diseases and other conditions. Blood donation is a one-time extraction of a certain amount of blood, which may cause the temporary loss of some blood cells and plasma in the body, and most of the plasma is water, so what is lost in blood donation is water rather than fat, and the body will usually recover automatically in a week or so. The sudden weight loss refers to the sudden reduction of body fat within a short period of time, and there is no inevitable connection between blood donation and sudden weight loss. The skinny after blood donation may be caused by indigestion, hyperthyroidism, tumor disease, etc. Indigestion may lead to the human body can not take in the required nutrients, hyperthyroidism leads to metabolic abnormalities, tumor disease will consume the human body’s nutrients, resulting in excessive nutritional depletion, and all of these situations will appear in the human body skinny situation. The situation of losing weight after donating blood, it is recommended to consult a doctor in a timely manner, under the guidance of the doctor to improve the examination, targeted treatment.