Disorders of Iron Kinetics and Heme Metabolism

Chapter 17: Disorders of Iron Kinetics and Heme Metabolism

Overview of Anemia

  • Definition of Anemia:

    • Anemia may result from impaired red blood cell (RBC) production, shortened RBC lifespan, or loss of RBCs from the body.

  • Types of Anemia:

    • Anemias associated with iron and heme are categorized as anemias of impaired production due to lack of components for hemoglobin assembly.

    • If iron is the limiting factor, these are termed iron-restricted anemias. Examples include:

    • Iron deficiency anemia

    • Anemia of chronic inflammation

Anemia Types and Mechanisms

  • Sideroblastic Anemia:

    • Inadequate protoporphyrin production leads to decreased heme and hemoglobin, despite excess iron.

    • Blockages in protoporphyrin production throughout the heme synthesis pathway cause porphyrin accumulation, resulting in anemia.

  • Hemochromatosis:

    • Excess iron accumulation without anemia, resulting from disrupted iron metabolism.

  • Iron-Loading Anemia:

    • Associated with chronic erythroid hyperplasia, seen in hemoglobinopathies and thalassemias due to heritable mutations affecting globin chain structure.

Causes of Iron Deficiency Anemia

  • Inadequate Iron Absorption:

    • Occurs when:

    • Iron absorption fails to meet the body’s demands.

    • Iron needs increase without increased intake.

    • There are chronic losses of hemoglobin (from blood loss or hemolysis).

  • Inadequate Iron Intake:

    • Iron deficiency develops when the erythron is starved of iron.

    • About 1 mg of iron is lost daily from the body, primarily through sloughed intestinal epithelial cells.

    • The body conserves iron efficiently, but inadequate intake depletes iron stores, slowing RBC production.

  • Increased Iron Demand:

    • Rapid growth phases (e.g., infancy, adolescence, pregnancy) increase iron requirements.

  • Impaired Absorption:

    • Conditions like celiac disease or inherited mutations in iron regulatory proteins can lead to persistent hepcidin production, inhibiting iron absorption.

Chronic Blood Loss and Its Impact

  • Mechanisms of Loss:

    • Chronic blood loss can stem from:

    • Repeated blood donations

    • Chronic hemorrhage (test conditions like ulcers, tumors)

    • Conditions such as menorrhagia in women can deplete iron stores.

  • Symptoms:

    • Severe symptoms may develop later, and iron is lost through various mechanisms including urinary losses in chronic hemolytic processes.

Pathogenesis of Iron Deficiency Anemia

  • Stages of Iron Deficiency:

    • Stage 1: Normal RBC production with declining storage iron.

    • Stage 2: Exhaustion of storage iron with normal but decreasing RBC production; indicators of iron-restricted erythropoiesis begin to show.

    • Stage 3: Frank anemia occurs as iron deficiency impacts hemoglobin production; microcytic and hypochromic RBCs are produced.

  • Normal Distribution of Iron:

    • Iron is stored in compartments:

    • Storage (ferritin)

    • Transport (transferrin)

    • Functional (hemoglobin and myoglobin).

Epidemiology of Iron Deficiency Anemia

  • At-Risk Populations:

    • Primarily affects menstruating women, pregnant women, and growing children who may not receive adequate dietary iron.

    • Rare in men due to coaching and other physiological factors.

  • Impact of Diet and Conditions:

    • Chronic disease, elderly individuals, and soldiers or athletes may also experience increased risk due to dietary inadequacies or physical strains.

Laboratory Diagnosis of Iron Deficiency

  • Includes blood tests for:

    • Serum Iron: Reflects iron in circulation.

    • Total Iron Binding Capacity (TIBC): Indicates transferrin levels; increases in deficiency.

    • Ferritin Level: Indicates stored iron.

    • Transferrin Saturation: Percentage reflecting iron saturation of transferrin.

  • Indicators of Iron Deficiency:

    • Low hemoglobin, high RDW, and characteristic blood film findings.

    • Automated hematology analyzers can assist in early detection of microcytosis and hypochromia.

Treatment of Iron Deficiency

  • Initial Steps:

    • Treat underlying causes (e.g., gastrointestinal pathology, chronic blood loss).

    • Iron supplementation is the standard treatment, typically with oral ferrous sulfate.

  • Response:

    • Reticulocyte counts should rise within a few days of therapy; hemoglobin should normalize within 2 months.

    • Treatment typically lasts several months to replenish iron stores adequately.

Anemia of Chronic Inflammation

  • Characteristics:

    • Associated with chronic disease states (infections, autoimmune diseases) leading to improved iron sequestering mechanisms due to increased hepcidin responses.

  • Laboratory findings typically show:

    • Mild anemia without reticulocytosis, normocytic or microcytic RBCs, and low serum iron with normal or increased ferritin.

Sideroblastic Anemias and Other Conditions

  • Sideroblastic Anemia:

    • Results from disrupted protoporphyrin production; demonstrates ringed sideroblasts on bone marrow examination.

    • Can be hereditary or acquired from toxins (e.g., lead poisoning).

  • Porphyrias:

    • Disorders characterized by impaired heme production across the synthesis pathway leading to elevated porphyrin levels.

Iron Overload Disorders

  • Diseases:

    • Primary (hereditary hemochromatosis) or secondary (chronic anemias, repetitive transfusions).

    • Associated with serious complications, including liver disease, diabetes, and heart failure.

  • Diagnosis and Treatment:

    • Elevated iron studies guide diagnosis; treatment often involves phlebotomy and/or iron chelation therapies.