Venesection refers to the removal of blood.  This procedure is performed for people who have too  many circulating red cells (polycythaemia) or iron overload (haemochromatosis).  It is similar to the procedure used for donating blood.  The frequency of venesections depends on the level of red cells or iron.  It may be weekly initially, until the level comes down, and then will be spaced out - sometimes to three or four times a year.  It is a lifelong process.