Iron is an essential element for oxygen transport within hemoglobin. Oddly enough it is the element that is missed the most in regards to adequate intake and proper nutrition. Over 1.62 billion people in the world are effected by anemia, which is most commonly caused by iron deficiency. Iron deficiency can be caused by chronic blood loss, and is most common in women and teenagers from loss of blood due to menses. Iron loss leads to increased fatigue and depression, pallor, and dry and splitting hair. It can also lead to confusion cognitive effects. Hemoglobin is made of four polypeptide chains, two of which are alpha, and two are beta that come together to form a tetramer heme group with iron located in the middle. Ferrous iron within each heme molecule reversibly binds to one oxygen molecule. With iron deficiency, there becomes a hemoglobin deficiency. A decreased hemoglobin lowers oxygen-carrying capacity leading to anemia. Anemia by definition is a reduced oxygen-carrying ability. Tissue hypoxia can wreak havoc on almost every cell of the body, and can shift the oxygen dissociation curve in an unfavorable direction. The structure of hemoglobin and its function and key elements can be reviewed here.
To understand iron deficiency its important to recognize important aspects of iron metabolism and transportation in cells. Review the Iron Absorption and Metabolism article here for that information. There are also laboratory values that give a good picture of the iron status within the body that one should pay attention to. Transferrin; which is measured as the total iron binding capacity (TIBC) indicates how much or how little iron is being transported throughout the body. Serum iron is an important indicator of the tissue iron supply, and finally serum ferritin gives a picture of iron storage status within the bone marrow and cells.
Iron Deficiency Anemia
There are three stages within iron deficiency. Each comes with their own classic picture of laboratory results and worsen from stage to stage. In the first stage, there is storage iron depletion. This is mild and the patient may not even feel a difference physically. The patients hemoglobin is normal, normal serum iron, and TIBC. There is however decreased ferritin which indicates that there is decreased storage of iron. The second stage of iron deficiency is characterized by transport iron depletion. The hemoglobin may or may not be abnormal, but there is increased TIBC, and decreased serum iron. An increased TIBC, means that there are more substrate (iron) binding spots within the transferrin molecule. This implies that less iron is binding, which when coupled with a decreased serum iron makes sense. The patient may experience mild anemia which comes with increased fatigue and pallor. A peripheral blood smear will most often start to exhibit anisocytosis and poikilocytosis. These reference indicators represent abnormal sized red cells and abnormal shaped red blood cells respectively. A good indicator is an increased RDW, an increased RDW indicates some degree of anisocytosis. This is accurate because the red blood cell is realizing the loss of this oxygen-carrying capacity so its trying to release red blood cells as fast it can from the bone marrow to compensate for the loss, and as a result these red blood cells will appear smaller in diameter and hypochromic. Hypochromasia indicates that there is less hemoglobin within the cell and there is more of a central pallor. The thought is that even though there is less hemoglobin within each cell, if the bone marrow can produce more of these red blood cells than normal then that equals out. This leads to a microcytic anemia, micro meaning small. Stage three of iron deficiency is often referred to as functional iron deficiency. Within this stage there is an unmistakable decrease in hemoglobin, serum iron, and ferritin. There is also a large increase in TIBC.
The overall effect of iron deficiency anemia on the body and on the bone marrow is ineffective erythropoiesis. The red cell production within the bone marrow is compromised. As a result, the bone marrow becomes hypercellular with red cell precursors reducing the M:E (Myeloid:Erythroid) ratio.
This picture depicts how a peripheral blood smear would illustrate iron deficiency anemia. The red cells are smaller and there is more of a central pallor to them, indicating a loss of hemoglobin. This is also called hypochromia.
This picture depicts a normal peripheral blood smear. The red blood cells are larger in size and they have more color to them.
Anemia of Chronic Disease
Anemia of chronic disease is another form of microcytic anemia similar to iron deficiency anemia. It usually arises from a chronic infection or from chronic inflammation, but its also associated with some malignancies. A buildup in inflammatory cytokines alters iron metabolism. IL-6, which is an inflammatory cytokine inhibits erythrocyte production. It also increases hepcidin production. Hepcidin blocks iron release from the macrophages and the hepatocytes by down-regulating ferroportin. Without ferroportin there is no transportation of iron throughout the body and no production of hemoglobin or red blood cells. Laboratory findings will usually demonstrate low serum iron, low TIBC, low transferrin, and an increased to normal ferritin. The reticulocyte count is also normal, and sometimes increased. Reticulocytes are released from the bone marrow in times of red cell shortages to compensate.
This is just a brief overview of iron deficiency anemia and other microcytic anemias. This is just the beginning, follow and look forward to more in-depth reviews of each microcytic anemia. Key differences to look for is the TIBC value. In iron deficiency anemia the TIBC is increased and in anemia of chronic disease the TIBC is decreased. Ferritin is increased in anemia of chronic disease because the stored iron can’t be released from cells and the bone marrow due to the increased hepcidin production. Also the degree of anemia is mild compared to the more severe iron deficiency anemia.