Red cell volume can be measured by injecting tagged red blood cells. All of the following are used to tag red cell, EXCEPT:

Red cell volume is the volume occupied by all the circulating red cells in the body. It can be measured by sustracting the plasma volume from total body water. It can also be measured by injecting tagged red blood cells and measuring the fraction of red cells that is tagged.51 Cr radio isotope of chromium is commonly used. Isotopes of iron(59Fe) and phosphate (32P)and antigenic tagging is also used. Ref: Ganong's Reveiw of Medical Physiology, 21st Editon, Page 3