Blood count results are not constant from one day to the next, and may show certain patterns of variation along with physiological activities. In clinical medicine, we need to distinguish and judge the influence of some physiological factors on blood cell counts in the human body in order to correctly diagnose and treat diseases. Leukocytes The physiological changes of leukocytes are: 1. The number of leukocytes in peripheral blood can be different at different times of the day; in the morning, when the whole body basal metabolism of hospitalized patients is at a lower level, the result of leukocyte count is relatively low, while it is generally higher in the afternoon than in the morning; 2. The overall leukocyte count of newborns is high, generally in the range of (15-20) × 109/L, and individually up to 30 × 109/L, which are all within the normal range; 4. The physiological increase in leukocytes during pregnancy for more than 5 months and delivery can reach 15 × 109/L, or even higher. The above leukocytosis can return to normal soon after the removal of the influencing factors and is caused by the transient release of leukocytes from the marginal pool into the circulating pool of peripheral blood; whereas leukocytosis of longer duration, such as pregnancy, is associated with increased release from the reservoir pool. Due to physiological factors of leukocytes, a change in leukocyte count within 30% (or even 50% according to some) within a day is a physiological fluctuation and is only meaningful if observed at regular and continuous follow-up. Platelets The physiological variation of platelets in normal people can vary from 6% to 10% within a day. They are generally lower in the morning and higher in the afternoon; they are higher after strenuous exercise and a full meal; they are lower in women at the beginning of menstruation and gradually increase after menstruation; they are higher in mid and late pregnancy and in newborns; they are higher in venous blood than in capillaries. Red blood cells Many physiological factors affect the red blood cell count results, such as finger blood collection than venous blood results are 10%-15% higher; sitting blood collection than lying 5%-15% higher, strenuous exercise will lead to a 10% increase in red blood cells, stress can lead to a temporary increase in red blood cells, usually the best at 7 a.m., under normal circumstances there can be fluctuations of 20% up and down. There is also a physiological increase in compensatory increase in red blood cells due to lack of oxygen in the body, such as in newborns, plateau life, strenuous physical labor (or long-term exercise). Adult males are higher than females, probably due to higher androgen levels in males and testosterone associated with the promotion of red blood cell hematopoiesis. Physiological decrease in red blood cells is seen in: infants and children aged 6 months to 2 years due to rapid growth and development resulting in a relative shortage of hematopoietic materials and increased blood volume; middle and late pregnancy, when blood volume increases significantly to accommodate the needs of the placental circulation and blood thinning; and elderly people with gradually declining hematopoietic function. The anemia caused by the above conditions is collectively called physiological anemia.