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

Interpretation of CBC Showing Microcytic Hypochromic Anemia with Thrombocytosis

This CBC shows iron deficiency anemia (IDA) with reactive thrombocytosis, requiring iron supplementation and investigation of the underlying cause, particularly focusing on gastrointestinal blood loss in adult females.

CBC Analysis

The CBC shows several abnormalities consistent with iron deficiency:

• Hemoglobin: 10.5 g/dL (Low)
• Hematocrit: 33.3% (Low)
• MCV: 79 fL (At lower limit of normal)
• MCH: 24.8 pg (Low)
• MCHC: 31.5 g/dL (At lower limit of normal)
• RDW: 15.9% (High)
• Platelets: 451 x10³/uL (High)

Diagnostic Interpretation

This pattern represents a classic microcytic hypochromic anemia with the following key features:

• Low hemoglobin and hematocrit indicating anemia
• Low/borderline MCV indicating microcytosis
• Low MCH indicating hypochromia
• Elevated RDW indicating variability in red cell size (anisocytosis)
• Thrombocytosis (elevated platelets) as a reactive finding

Differential Diagnosis

1. Iron deficiency anemia (most likely) 1

   • Most common cause of microcytic hypochromic anemia
   • Associated with reactive thrombocytosis
   • Elevated RDW is characteristic

2. Thalassemia trait

   • Usually has very low MCV out of proportion to the degree of anemia
   • Normal or minimally elevated RDW
   • Normal or decreased platelet count

3. Anemia of chronic disease

   • Can present with microcytosis but typically normocytic
   • Usually normal or low platelets

4. Sideroblastic anemia

   • Rare genetic disorder
   • Would require bone marrow examination to diagnose 1

Diagnostic Workup

To confirm iron deficiency:

1. Iron studies:

   • Serum ferritin (most specific test for iron deficiency)
     • <15 μg/L is highly specific for iron deficiency
     • <45 μg/L has good specificity (0.92) 1
   • Transferrin saturation (<20% suggests iron deficiency)
   • Serum iron (low in iron deficiency)

2. If iron studies are equivocal:

   • Consider measuring serum transferrin receptor levels
   • Free erythrocyte protoporphyrin (elevated in iron deficiency) 2

Etiology Investigation

Once iron deficiency is confirmed, investigate the cause:

1. In premenopausal women:

   • Menstrual blood loss (most common cause)
   • Pregnancy/recent childbirth
   • Inadequate dietary intake

2. In all patients:

   • GI blood loss (most common cause in men and postmenopausal women)
     • Upper endoscopy and colonoscopy are recommended
   • Malabsorption (celiac disease, post-surgical)
   • Frequent blood donation
   • Medication-induced (NSAIDs, anticoagulants)

Management

1. Iron replacement therapy:

   • Oral iron supplementation (first-line)
     • Ferrous sulfate 325 mg (65 mg elemental iron) 1-3 times daily
     • Take on empty stomach with vitamin C to enhance absorption
     • Continue for 3-6 months after hemoglobin normalizes to replenish stores

2. Consider parenteral iron if:

   • Oral iron intolerance
   • Malabsorption
   • Ongoing blood loss exceeding oral replacement capacity 3

3. Monitor response:

   • Reticulocyte count should increase within 1 week
   • Hemoglobin should rise by approximately 1-2 g/dL every 2-3 weeks
   • Continue iron therapy for 3-6 months after hemoglobin normalizes

Important Considerations

• Thrombocytosis (platelets 451 x10³/uL) is reactive in iron deficiency and typically resolves with iron replacement
• Do not stop at treating the anemia - identifying and addressing the underlying cause is essential
• GI malignancy must be excluded in men and postmenopausal women with iron deficiency anemia 1
• Rare genetic causes of microcytic anemia should be considered if standard treatment fails or if there's a family history 1, 4

Pitfalls to Avoid

1. Treating without confirming diagnosis - always confirm iron deficiency with appropriate testing
2. Missing underlying serious pathology - especially GI malignancy
3. Stopping iron too early - continue for 3-6 months after hemoglobin normalizes
4. Ignoring poor response - if no improvement after 4-6 weeks, reassess diagnosis and compliance
5. Overlooking inflammation - in inflammatory states, ferritin may be falsely elevated (up to 100 μg/L can still represent iron deficiency) 1