- Menstrual blood loss and increased iron requirements of pregnancy are the most common causes in the developed world.
- Gastrointestinal (GI) blood loss is the presumed etiology in most other patients.
- Decreased iron absorption (celiac disease, postgastrectomy, Helicobacter pylori ) or increased iron requirements (lactation) may also lead to iron deficiency.
- Chronic intravascular hemolytic anemia may lead to iron deficiency (e.g., long-distance running).
- Iron-deficiency anemia is the most common cause of anemia in the geriatric patient.
- A complete analysis of iron deficiency requires identification of the underlying cause.
- Blood loss (melena, menorrhagia, frequent blood donation).
- Pica (consumption of substances such as ice, starch, or clay) may be present.
- Splenomegaly, koilonychia (spoon nail), and the Plummer-Vinson's syndrome (glossitis, dysphagia, and esophageal webs) are rare findings. The presence of telangiactasias or heme-positive stool may help to identify the source of blood loss.
- MCV is usually normal in early iron deficiency. As the Hct falls below 30%, anisocytosis increases and hypochromic microcytic cells appear, followed by a decrease in the MCV.
- Platelet count may be increased.
- Peripheral smear demonstrates hypochromic, microcytic red cells and occasional pencil cells and target cells.
- Iron testing
- Serum ferritin level of <10 ng/mL in women or 20 ng/mL in men is indicative of iron deficiency.
- Ferritin is an acute-phase reactant, so that normal levels may be seen in inflammatory states, liver disease, or malignancy despite low iron stores.
- A serum ferritin level of >200 ng/mL generally indicates adequate iron stores regardless of other underlying conditions.
- Serum iron is usually low (<50 mcg/dL), and total iron-binding capacity is increased (>420 mcg/dL) in iron deficiency, but these values may fluctuate in a number of common clinical conditions and hence are less reliable indicators of iron stores than the serum ferritin.
- Bone marrow aspirate is the definitive test for iron deficiency.
- It is the earliest indicator of iron deficiency.
- It is useful when diagnosis of iron deficiency is not clear.
- Therapeutic challenge with supplemental iron can help to identify anemias that are iron responsive when diagnosis is uncertain.
- Oral iron
- Ferrous sulfate, 325 mg (65 mg elemental iron) PO tid taken between meals to maximize absorption, usually corrects the anemia and repletes iron stores (as determined by normalization of the serum ferritin) over approximately 6 months.
- Concomitant use of acid-neutralizing medications is an underappreciated cause of an impaired response to oral iron.
- GI side effects, such as constipation, cramping, diarrhea, or nausea, develop in approximately 25% of patients. These side effects can be decreased by initially administering the drug with meals or once a day and increasing the dose as tolerated.
- Ferrous gluconate and fumarate at a similar dose may be better-tolerated alternative therapies.
- Iron polysaccharide complex (Niferex) contains 150 mg of elemental iron and, given twice daily, is as effective as other preparations at a similar cost and seems to have fewer GI side effects.
- Ferric forms of oral iron, sustained-release or enteric-coated preparations, dissolve poorly and generally should not be recommended.
- Lower doses of ferrous sulfate are better tolerated and as effective in geriatric patients.
- Noncompliance is the most common reason for a poor response to oral therapy.
- Parenteral iron
- Indications for parenteral iron include poor enteral absorption, continued blood loss, or intolerance to oral iron.
- Iron dextran (Infed) Test dose: Allergic reactions or anaphylaxis to iron dextran occur in about 1 in 300 patients, thus a 25-mg test dose in 50 mL of normal saline over 5-10 minutes should be administered initially. If a reaction does not occur within 1 hour, proceed with administration of the total dose.
- Total dose: Dose in mL = (0.0442 (desired hemoglobin - current hemoglobin) ideal body weight) + (0.26 ideal body weight) The total dose (generally between 1 and 2 g) should be diluted in 500 mL of normal saline and administered over 4-6 hours.
- Ferric gluconate (Ferrlecit) is dosed at 125 mg and may be administered weekly or up to three times per week with hemodialysis. The risk of anaphylaxis is significantly less with ferric gluconate.
- With therapy, the reticulocyte count peaks in 5-10 days, and the Hb rises over 1-2 months.