[Erythropoiesis and erythrocytes in children, physiology and standards].

Foetal erythropoiesis has its own particularities: it takes place mostly in the liver for a long time, is macrocytic and is strongly stimulated, then suppressed at birth; the level of haemoglobin F, which has specific properties, is still high at birth. In children, the site of sampling must be clearly indicated in view of possible discrepancies between capillary and venous blood samples. Hemoglobin levels and red cell indices vary with age, and it is indispensable to take as reference standards that change in each period of life from foetal life to adolescence. The polycythaemia and macrocytosis observed at birth is followed by a period when the haemoglobin level is relatively low and microcytosis develops. Adult values will be reached gradually during the second part of childhood.