Iron Deficiency Anemia

Overview
  • Iron Deficiency Anemia is a microcytic anemia, resulting in small hypochromic poikilocytes on peripheral blood smear, and is caused by a chronic imbalance between iron absorption and demand, most frequently due to chronic blood loss.
Pathophysiology
  • Overview
    • Iron Deficiency Anemia results from a long-term imbalance between the intake of iron and the physiological demand for this metal. The etiologies that can lead to this imbalance are discussed further below; however, regardless of the cause, iron deficiency yields a graded set of consequences, the end stage of which is anemia.
  • Stage 1: Mobilization of Iron Stores
    • Roughly 15% of the total body's iron is stored as a reservoir in a ferritin-bound form within hepatocytes and reticuloendothelial macrophages. When demand for iron outstrips intake, this ferritin-bound iron is mobilized.
  • Stage 2: Laboratory Changes
    • As ferritin-bound stores of iron are exhausted, the levels of serum ferritin begin to fall. Further exhaustion of supplies yield reductions in the concentration of iron-bound transferrin and ultimately reductions in the serum concentration of iron itself. Taken together these changes yield the classic laboratory sequelae of iron deficiency anemia: Decreased serum ferritin, decreased serum iron, and increased serum Total Iron Binding Capacity (TIBC).
  • Stage 3: Anemia
    • As iron deficiency becomes more severe, bone marrow erythropoiesis is ultimately affected and hemoglobin concentrations begin to fall. The morphology of red cells produced are characteristically small (i.e. "Microcytic"), less densely packed with hemoglobin (i.e. "Hypochromic"), and display a large variability in size (i.e. Poikilocytic).
Etiologies
  • Overview
    • An imbalance between iron absorption and physiological demand may be generated via three mechanisms: Reduced dietary absorption, increased anabolic states, or increased iron loss.
  • Reduced Iron Absorption
    • Reduced Iron Absorption is most likely to occur due to insufficient dietary intake, especially in certain geographic regions. Intestinal malabsorption of iron is relatively rare but may occur in those with Celiac Disease or post-surgical patients where proximal sections of the small bowel were removed.
  • Increased Anabolic States
    • Infants, growth-spurting adolescents, and pregnant women are all in states of intense anabolism, and thus require elevated levels of iron absorption to keep up with demand. Consequently, these patient populations can easily dip into iron deficiency anemia.
  • Increased Iron Loss
    • Increases in iron loss occur almost exclusively via chronic blood loss. Indeed, this is the most common cause of iron deficiency anemia. Menstruation is typically the cause in reproductively aged women. However, in non-menstruating patients, chronic blood loss may go undetected for long periods of time from occult GI sources. A relatively long list of sources of Upper and Lower GI Bleeding can be to blame but the most feared cause is that of colorectal carcinoma, although gastritis, peptic ulcer disease and other neoplasms are not infrequent. As a side note, in patient's suffering through long hospital courses, iatrogenic chronic blood loss is not uncommon due to frequent daily lab draws.
Clinical Consequences
  • Iron deficiency anemia shares the same basic clinical consequences as those of any other anemia (See page).