Erythrocyte Protoporphyrin

Blood protoporphyrin (PROTO) concentration in man and animals has been studied as a possible means of assessing the relationship between iron supply and marrow requirements. There appear to be two fractions of PROTO: one at a level of about 30 µg/ 100 ml unrelated to either iron supply or cell age, and a second fraction that appears when iron supply is limited and that has an elution T_½ of 2-4 wk. Animal studies have demonstrated that increased erythropoiesis and reticulocytosis per se do not change PROTO, providing that there is an adequate (increased) plasma iron level. In phlebotomized man, within 1 or 2 wk following a decrease in plasma iron saturation to less than 15%, the PROTO levels become significantly elevated. In more chronic disease states associated with near normal rates of erythropoiesis, a transferrin saturation less than 15% is usually associated with increased PROTO. In patients with hemolytic anemia, the PROTO level rises even though plasma iron and per cent saturation values are higher. Evidence is presented suggesting that both the extent of marrow proliferation and erythropoietin stimulation may affect the PROTO response. The red cell PROTO concentration is an important parameter for assessing iron-deficient erythropoiesis, either relative or absolute. The usefulness of this parameter is compared with red cell indices, plasma iron, and transferrin saturation data.