Hematology · Microcytic Anemia
The facts most likely to be tested
Iron deficiency anemia is the most common cause of microcytic anemia, characterized by a low mean corpuscular volume (MCV) and low mean corpuscular hemoglobin (MCH).
The most sensitive and specific laboratory test for iron deficiency is a low serum ferritin level.
Laboratory findings in iron deficiency anemia classically show low serum iron, low ferritin, high total iron-binding capacity (TIBC), and low transferrin saturation.
Chronic blood loss, particularly from the gastrointestinal tract in adults, is the most common etiology of iron deficiency anemia in developed countries.
Peripheral blood smear findings in iron deficiency anemia include hypochromic, microcytic red blood cells and pencil-shaped cells.
Patients may present with classic physical exam findings such as atrophic glossitis, angular cheilitis, or koilonychia (spoon nails).
Pica, specifically pagophagia (craving for ice), is a highly specific clinical symptom associated with iron deficiency anemia.
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A 58-year-old male presents to the clinic complaining of progressive fatigue and exertional dyspnea over the past three months. He reports a change in bowel habits with occasional dark, tarry stools. Physical examination reveals pale conjunctiva, atrophic glossitis, and koilonychia. Laboratory studies demonstrate a hemoglobin of 9.2 g/dL, MCV of 74 fL, and a serum ferritin of 8 ng/mL. A fecal occult blood test is positive.
What is the most appropriate next step in the management of this patient?
Colonoscopy
The patient has iron deficiency anemia confirmed by low ferritin and microcytosis; given his age and symptoms of occult GI bleeding, the most important next step is to identify the source of blood loss via colonoscopy to rule out malignancy.
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Etiology / Epidemiology
Most common anemia worldwide; caused by chronic blood loss (menorrhagia, GI malignancy) or malabsorption.
Clinical Manifestations
Presents with fatigue, pica, and koilonychia. Glossitis and angular cheilitis are classic physical exam findings.
Diagnosis
Ferritin < 30 ng/mL is the most sensitive/specific test. Expect microcytic, hypochromic indices.
Treatment
Oral ferrous sulfate is first-line. Avoid antacids/calcium as they inhibit absorption.
Prognosis
Usually excellent; monitor reticulocyte count at 1-2 weeks to confirm marrow response.
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Epidemiology & Etiology
In adult males and postmenopausal females, GI malignancy must be ruled out via endoscopy. Premenopausal women typically suffer from menorrhagia. Infants may develop deficiency due to excessive cow's milk intake.
Pertinent Anatomy
Iron is primarily absorbed in the duodenum. Chronic inflammation or surgical resection of the proximal small bowel significantly impairs iron uptake.
Pathophysiology
Iron depletion occurs in stages: storage iron (ferritin) is exhausted first, followed by serum iron, and finally hemoglobin synthesis. Reduced iron availability leads to microcytic, hypochromic RBCs. The body compensates with increased transferrin production, resulting in elevated TIBC.
Clinical Manifestations
Patients often report pica (craving ice or dirt) and restless leg syndrome. Physical exam reveals koilonychia (spoon nails), atrophic glossitis, and angular cheilitis. Severe cases may present with Plummer-Vinson syndrome (esophageal webs, dysphagia, and anemia).
Diagnosis
The serum ferritin level is the gold standard diagnostic test, with values < 30 ng/mL being diagnostic. Peripheral smear shows microcytosis and hypochromia. If ferritin is indeterminate, a bone marrow biopsy (iron stain) is the definitive, though rarely performed, test.
Treatment
Oral ferrous sulfate is the first-line treatment. Take with Vitamin C (ascorbic acid) to enhance absorption. Do not take with antacids, calcium, or tea as these decrease bioavailability. If oral therapy fails or is poorly tolerated, IV iron sucrose is indicated.
Prognosis
Most patients show a rise in reticulocyte count within 7-10 days. Hemoglobin should normalize within 6-8 weeks. Iron stores should be replenished for 3-6 months after normalization to prevent recurrence.
Differential Diagnosis
Thalassemia: normal or elevated ferritin with target cells
Anemia of Chronic Disease: elevated ferritin, low TIBC
Sideroblastic Anemia: ringed sideroblasts on bone marrow biopsy
Lead Poisoning: basophilic stippling on peripheral smear
Hemoglobinopathy: abnormal hemoglobin electrophoresis