What is the interpretation and management of a CBC showing microcytic hypochromic anemia?

Interpretation of CBC Results: Microcytic Hypochromic Anemia with Elevated RDW

This CBC demonstrates microcytic hypochromic anemia with elevated RDW (15.6%), which strongly suggests iron deficiency anemia as the primary diagnosis, and you should immediately check serum ferritin to confirm iron deficiency before initiating oral iron supplementation. 1, 2

Key CBC Findings and Their Significance

• MCV 78 fL (low): Indicates microcytosis, meaning red blood cells are smaller than normal 3
• MCH 24.2 pg (low): Confirms reduced hemoglobin content per red cell 3
• MCHC 30.9 g/dL (low): Demonstrates hypochromia, indicating decreased hemoglobin concentration within red cells 3
• RDW 15.6% (elevated): The elevated RDW >14.0% combined with low MCV strongly points toward iron deficiency anemia rather than thalassemia trait, which typically presents with RDW ≤14.0% 1, 2

Immediate Diagnostic Workup

Measure serum ferritin first as it is the most specific test for iron deficiency, with levels <30 μg/L indicating low body iron stores, though a cutoff of 45 μg/L provides optimal sensitivity and specificity 1, 2

• Check transferrin saturation (TSAT), which is more sensitive for detecting iron deficiency than hemoglobin alone 1, 2
• If ferritin is normal or elevated (>20 μg/L) despite microcytosis, consider genetic disorders of iron metabolism or heme synthesis rather than simple iron deficiency 3, 4
• Hemoglobin electrophoresis should be ordered if RDW were normal to exclude β-thalassemia trait, but the elevated RDW here makes thalassemia less likely 2

Treatment Algorithm Based on Ferritin Results

If Ferritin <45 μg/L (Iron Deficiency Confirmed):

Start oral iron supplementation with ferrous sulfate 200 mg (65 mg elemental iron) three times daily for at least three months after correction of anemia to replenish iron stores 1, 2

• Add ascorbic acid (vitamin C) to enhance iron absorption 1
• Alternative formulations include ferrous gluconate or ferrous fumarate if ferrous sulfate causes intolerable gastrointestinal side effects 1
• A good response is defined as hemoglobin rise ≥10 g/L (≥1 g/dL) within 2 weeks, which confirms iron deficiency 1, 2
• Investigate the source of iron loss in adults, as occult gastrointestinal malignancy must be excluded 2

If Ferritin Normal/Elevated (>45 μg/L):

• Measure serum iron and transferrin saturation to distinguish between genetic disorders 3, 5
• Consider bone marrow examination to look for ring sideroblasts if ferritin is normal/high with abnormal iron studies, which is definitive for sideroblastic anemia 4, 6
• Genetic testing is crucial for definitive diagnosis in cases with extreme microcytosis and normal/elevated ferritin 4

Specific Management for Genetic Disorders (If Identified)

X-linked Sideroblastic Anemia (ALAS2 defects):

• Trial of pyridoxine (vitamin B6) 50-200 mg daily initially, with maintenance dose of 10-100 mg daily once response is achieved 4, 1

Iron Refractory Iron Deficiency Anemia (TMPRSS6 defects):

• Intravenous iron (iron sucrose or ferric gluconate) is required as these patients are resistant to oral iron 1
• Monitor ferritin and do not exceed 500 mg/L to avoid iron overload risk 1

SLC25A38 or severe sideroblastic anemia:

• Hematopoietic stem cell transplantation is the only curative option 4, 1
• Symptomatic treatment includes erythrocyte transfusions and chelation therapy 1

Monitoring and Follow-up

• Monitor hemoglobin concentration and red cell indices at three-monthly intervals for one year, then after a further year 1, 2
• For patients on oral iron, expect hemoglobin increase of at least 2 g/dL within 4 weeks 1
• Provide additional oral iron if hemoglobin or MCV falls below normal 1, 2
• For patients receiving multiple transfusions or long-term iron therapy, monitor for iron overload with MRI of the liver in specific cases 4, 1

Critical Pitfalls to Avoid

• Do not overlook combined deficiencies: Iron deficiency can coexist with B12 or folate deficiency, requiring evaluation of vitamin levels 2
• Do not miss the 7% of patients with both thalassemia trait and iron deficiency: Check ferritin even when thalassemia is diagnosed 2
• Do not assume normal hemoglobin excludes iron deficiency: Hypochromic microcytic changes can precede anemia development 2
• For non-responders to oral iron: Consider intravenous iron if malabsorption is present, or re-evaluate for genetic disorders of iron metabolism 1, 2