hgb dl transfusion hemoglobin days blood allowed prior rbc criteria gm hemoglobin dl hgb transfusion creatinine days si equal prior transfusions hemoglobin dl hgb allowed receive blood days permitted permissible transfusion meet inclusion blood allowed criteria mm count hb neutrophil hgb hemoglobin dl days anemia starting gr mg therapy treatment transfusion hemoglobin dl permitted days blood prior administration past preceding