Iron (Fe)

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Subject: Iron (Fe)

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Definition

  • Iron exists in the body in many forms: hemoglobin in circulating red cells and developing erythroblasts, iron-containing proteins such as myoglobin and cytochromes, and bound to transferrin and storage in the form of ferritin and hemosiderin. Iron homeostasis is regulated strictly at the level of intestinal absorption and release of iron from macrophages. The serum iron level reflects Fe3+ bound to transferrin, not free Hb in serum.

  • Normal range:

    • Female: 28–170 μg/dL

    • Male: 45–182 μg/dL

Use

  • Diagnosis of blood loss

  • Differential diagnosis of anemias

  • Diagnosis of hemochromatosis and hemosiderosis

  • Evaluation of iron deficiency; should always be measured with TIBC

  • Diagnosis of acute iron toxicity, especially in children

  • Evaluation of thalassemia and sideroblastic anemia

  • Monitor response to treatment for anemia

Increased In

  • Idiopathic hemochromatosis

  • Hemosiderosis of excessive iron intake (e.g., repeated blood transfusions, iron therapy, iron-containing vitamins) (may be >300 μg/dL)

  • Decreased formation of RBCs (e.g., thalassemia, pyridoxine deficiency anemia, PA in relapse)

  • Increased destruction of RBCs (e.g., hemolytic anemias)

  • Acute liver damage (degree of increase parallels the amount of hepatic necrosis) (may be >1,000 μg/dL); some cases of chronic liver disease

  • Progesterone birth control pills (may be >200 μg/dL) and pregnancy

  • Premenstrual elevation by 10–30%

  • Acute iron toxicity; serum iron-to-TIBC ratio is not useful for this diagnosis

  • Repeated transfusions

  • Lead poisoning

  • Acute hepatitis

  • Vitamin B6 deficiency

Decreased In

  • Iron deficiency anemia

  • Normochromic (normocytic or microcytic) anemias of infection and chronic diseases (e.g., neoplasms, active collagen diseases)

  • Acute and chronic infection

  • Carcinoma

  • Hypothyroidism

  • Postoperative state and kwashiorkor

  • Nephrosis (because of loss of iron-binding protein in urine)

  • PA at onset of remission

  • Menstruation (decreased by 10–30%)

Limitations

  • Serum iron is not reliable as the primary test to identify iron deficiency or screening for hemochromatosis and other iron overload diseases. For these conditions, a serum TIBC, percent transferrin saturation, and ferritin assay are recommended.

  • Diurnal variation—normal values in midmorning, low values in midafternoon, very low values (approximately 10 μg/dL) near midnight. Diurnal variation disappears at levels <45 μg/dL.

  • Iron dextran administration causes increase for several weeks (may be >1,000 μg/dL).

  • Ingestion of oral contraceptives will elevate iron and/or total iron-binding capacity values.

  • Not recommended for patients undergoing treatment with deferoxamine or other iron-chelating compounds.

  • Ingestion of iron (including iron-fortified vitamins or supplements) may cause transient elevated iron levels.

 
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