Hemochromatosis | Primary Issues: One unit of blood or 500 mL (range 250-600 mL) is generally withdrawn weekly or biweekly to achieve a serum ferritin level below 50 ng/mL.[6,18] Normalization of serum ferritin usually requires removal of 8 to 25 units of blood, after which frequency of phlebotomy can generally be reduced to 1 unit every 2 to 6 months.[7,18,20]