10.5 is considered to be the ideal Hb level to maintain. Below this, bone marrow activity increases rapidly. Even at 9, the bone marrow is about 2-3 times more active than normal. This means more potential for bone expansion and also more bad red blood cells for the spleen and other organs to filter out. It also means more chance for growth of extramedullary hematopoiesis, which are commonly found in conditions of chronically low hemoglobin levels. So, if at all possible, keep the Hb up.