Illustration of an abnormal red blood cell (erythrocyte) known as an eccentrocyte. These abnormal red blood cells appear to have all their haemoglobin (red pigment) shifted to one side of the cell, leaving a clear area on the other side. This is a result of oxidative stress causing the two layers of the cell membrane to fuse, leaving no space for haemoglobin. Oxidative stress may be caused by certain drugs or toxins or inherited enzymopathies.