The endogenous concentration of Hp in the brain is very low and in a recent study in human adults the resting state capacity of the intrathecal CD163-Hp-Hb clearing system was described to be 50,000-fold lower than that of the circulation and this system was quickly saturated following subarachnoidal hemorrhage with a residual inability to deal effectively with extracellular Hb [34]. This evidence concerns the gene GSTM1 and subarachnoid hemorrhage.