What are the typical laboratory findings in microcytic hypochromic anemia?

Laboratory Findings in Microcytic Hypochromic Anemia

Microcytic hypochromic anemia is characterized by low hemoglobin, decreased mean corpuscular volume (MCV < 80 μm³), low mean corpuscular hemoglobin (MCH), and reduced mean corpuscular hemoglobin concentration (MCHC), with iron deficiency being the most common cause. 1

Key Laboratory Parameters

Complete Blood Count (CBC) Findings:

• Hemoglobin: Decreased (<13 g/dL for men, <12 g/dL for women)
• MCV: Low (<80 μm³)
• MCH: Reduced
• MCHC: Reduced
• RDW (Red cell distribution width): Typically elevated, especially in iron deficiency 2, 1
• Peripheral blood smear: Shows small (microcytic) and pale (hypochromic) red blood cells; may show pencil-shaped red cells in iron deficiency 2

Iron Studies:

• Serum ferritin:
  • Most sensitive single test for iron deficiency 3
  • <30 μg/L in patients without inflammation 2
  • <100 μg/L may still indicate iron deficiency in the presence of inflammation 2, 1
• Serum iron: Decreased
• Total iron binding capacity (TIBC): Increased
• Transferrin saturation: Decreased (<20%, often <16%) 2

Additional Tests:

• Reticulocyte count: Low or inappropriately normal for the degree of anemia 2
• Bone marrow iron stores: Absent in iron deficiency (gold standard but rarely needed) 4
• Serum transferrin receptor: Elevated in iron deficiency, helps differentiate from anemia of chronic disease 1

Differential Diagnosis of Microcytic Anemia

The laboratory findings can help distinguish between different causes of microcytic anemia:

1. Iron Deficiency Anemia:

   • Very low ferritin
   • High TIBC
   • Low transferrin saturation
   • Elevated RDW
   • Progressive decrease in MCV as deficiency worsens 5

2. Thalassemia:

   • Normal or elevated ferritin
   • Normal iron studies
   • Disproportionately low MCV compared to degree of anemia
   • Normal or slightly elevated RDW
   • Hemoglobin electrophoresis may show abnormal hemoglobin patterns 5, 6

3. Anemia of Chronic Disease:

   • Ferritin >100 μg/L
   • Low transferrin saturation (<20%)
   • Low or normal TIBC
   • Usually normocytic but can be microcytic in long-standing cases 2, 1

4. Sideroblastic Anemia:

   • Elevated ferritin
   • Increased serum iron
   • Normal or elevated transferrin saturation
   • Ring sideroblasts on bone marrow examination 6

Special Considerations

• In patients with combined iron deficiency and anemia of chronic disease, ferritin may be between 30-100 μg/L 2
• In cyanotic congenital heart disease with iron deficiency, red cells become microcytic and hypochromic with decreased oxygen-carrying capacity and reduced deformability 2
• Pregnant women have higher iron requirements and may develop microcytic anemia more readily 1

Common Pitfalls

• Relying solely on MCV for diagnosis without complete iron studies
• Misinterpreting ferritin levels in the presence of inflammation (ferritin is an acute phase reactant)
• Failing to consider combined etiologies (e.g., iron deficiency with thalassemia trait)
• Not accounting for the time-sensitive nature of certain tests like percent hypochromic red blood cells (PHRBC) 2
• Overlooking the need to investigate the underlying cause of iron deficiency, particularly gastrointestinal bleeding in non-menstruating patients 2

By systematically evaluating these laboratory parameters, clinicians can accurately diagnose microcytic hypochromic anemia and determine its underlying cause, leading to appropriate treatment strategies.