What are the next steps in managing microcytic anemia in an 18-year-old with a Hemoglobin (Hb) of 10.9 g/dL, Mean Corpuscular Volume (MCV) of 75 fL, Mean Corpuscular Hemoglobin (MCH) of 23.3 pg, and Mean Corpuscular Hemoglobin Concentration (MCHC) of 31.1 g/dL?

Management of Microcytic Anemia in an 18-Year-Old

The next step in managing this 18-year-old patient with microcytic anemia (Hb 10.9 g/dL, MCV 75 fL, MCH 23.3 pg, MCHC 31.1 g/dL) should be serum ferritin testing to confirm iron deficiency, followed by oral iron supplementation with ferrous sulfate 200 mg three times daily if iron deficiency is confirmed. 1, 2

Diagnostic Evaluation

Initial Laboratory Testing

• Serum ferritin is the most specific test for iron deficiency, with levels <15 μg/L indicating absent iron stores and <30 μg/L indicating low body iron stores 1
• A ferritin cut-off of 45 μg/L provides optimal sensitivity and specificity for iron deficiency in clinical practice 1
• Transferrin saturation (TSAT) should be evaluated as it is more sensitive for detecting iron deficiency than hemoglobin concentration alone 1
• The combination of low MCV with elevated RDW (>14.0%) strongly suggests iron deficiency anemia, while low MCV with normal RDW (≤14.0%) suggests thalassemia minor 1, 3

Additional Testing to Consider

• If serum ferritin is normal or elevated, further evaluation should include total iron-binding capacity, serum iron level, and possibly hemoglobin electrophoresis to differentiate between other causes of microcytic anemia 3
• In patients with unexplained microcytic anemia despite normal iron studies, consider genetic disorders of iron metabolism or heme synthesis 4, 1

Treatment Algorithm

First-Line Treatment

• For confirmed iron deficiency anemia, start oral iron supplementation with ferrous sulfate 200 mg three times daily (equivalent to 65 mg elemental iron per tablet) 1, 2, 5
• Continue treatment for at least three months after correction of anemia to replenish iron stores 1, 2
• Alternative formulations include ferrous gluconate and ferrous fumarate if ferrous sulfate is not tolerated 1
• Adding ascorbic acid can enhance iron absorption 1

Monitoring Response

• A good response to iron therapy is defined as a hemoglobin rise ≥10 g/L within a 2-week timeframe, which confirms iron deficiency 1, 2
• Monitor hemoglobin concentration and red cell indices at three-monthly intervals for one year and then after a further year 1
• Provide additional oral iron if hemoglobin or MCV falls below normal 1

For Non-Responders

• For patients who fail to respond to oral iron therapy, consider:
  • Intravenous iron if there is malabsorption 1, 2
  • Evaluation for other causes of microcytic anemia including thalassemia traits 2, 3
  • Testing for genetic disorders of iron metabolism or heme synthesis 4, 2

Investigation of Underlying Cause

• In men and post-menopausal women, iron deficiency anemia is most commonly caused by gastrointestinal blood loss or malabsorption 4

• In an 18-year-old, common causes to investigate include:

  • Menstrual blood loss if female 4
  • Gastrointestinal blood loss 4, 3
  • Poor dietary intake 4
  • Malabsorption (including celiac disease) 4, 1
  • NSAID use 4

• If iron deficiency is confirmed, further investigation may be warranted to identify the underlying cause 6, 3

• For gastrointestinal blood loss, upper and lower gastrointestinal endoscopy may be necessary depending on risk factors and severity 4

Special Considerations

• Avoid overlooking combined deficiencies, such as iron deficiency coexisting with B12 or folate deficiency 1, 7
• Consider thalassemia trait in patients with microcytosis who do not respond to iron therapy, especially if RDW is normal 1, 3
• Genetic testing should be considered in patients with refractory microcytic anemia despite adequate iron supplementation 1
• Family screening may be recommended if genetic disorders affecting iron metabolism are diagnosed 1