Is glucose‑6‑phosphate dehydrogenase deficiency a normocytic hereditary hemolytic anemia?

G6PD Deficiency: Classification as Normocytic Hereditary Hemolytic Anemia

Yes, glucose-6-phosphate dehydrogenase (G6PD) deficiency is a normocytic hereditary hemolytic anemia. 1

Hematologic Classification

G6PD deficiency belongs to the category of hereditary nonspherocytic hemolytic anemias (HNSHA), which are characteristically normocytic and normochromic. 1 This classification distinguishes it from membrane disorders like hereditary spherocytosis, which may show microcytosis, and from hemoglobinopathies with their characteristic morphologic changes.

Key Laboratory Features

• Red cell indices: The anemia is normocytic (normal MCV) and normochromic (normal MCH/MCHC), indistinguishable from other chronic anemias when only mean corpuscular volume is considered. 2

• Peripheral blood smear: Unlike membrane disorders, G6PD deficiency shows no specific morphologic abnormalities on routine examination—only mild anisocytosis and poikilocytosis similar to other enzymopathies. 32

• Diagnostic morphologic clue: When present, bite cells or blister cells are characteristic of G6PD deficiency and should prompt targeted enzyme testing. 3

Clinical Presentation Patterns

G6PD deficiency manifests in two distinct clinical forms:

Acute Episodic Hemolysis (Most Common)

• Approximately 500 million individuals with polymorphic G6PD mutations remain asymptomatic throughout their lifetime but are vulnerable to acute, sometimes severe hemolytic crises. 4

• Triggers include:

  • Fava bean ingestion
  • Oxidative drugs (primaquine, rasburicase)
  • Infection (less commonly) 4
  • Metabolic stress from newly diagnosed diabetes mellitus 5

Chronic Nonspherocytic Hemolytic Anemia (Rare)

• Approximately one-half of G6PD mutations are sporadic and rare, causing chronic hemolysis even without oxidative stress. 4

• These Class 1 variants present with:

  • Persistent reticulocytosis
  • Elevated lactate dehydrogenase
  • Indirect hyperbilirubinemia
  • Reduced or absent haptoglobin 367

• Chronic cases may develop gallstones and require intermittent transfusions during acute exacerbations. 6

Diagnostic Approach

When to Suspect G6PD Deficiency

• Hemolytic anemia with normal peripheral smear morphology (or bite/blister cells when present) in the context of oxidative stress or chronic unexplained hemolysis. 3

• Hemolysis that cannot be explained by spherocytes (which would suggest hereditary spherocytosis or autoimmune hemolytic anemia with positive DAT). 3

Confirmatory Testing

• Quantitative spectrophotometric enzyme assay measuring G6PD activity is the gold standard. 8

• Rapid fluorescent spot test detecting NADPH generation from NADP serves as a screening tool. 8

• Critical pitfall: Enzyme levels may appear falsely normal during acute hemolysis due to marked reticulocytosis (young red cells have higher enzyme activity) or after recent transfusion; results must be corrected for reticulocyte count. 3

• Molecular genetic testing via PCR or next-generation sequencing panels identifies specific mutations and enables family counseling. 38

Important Clinical Caveats

• G6PD deficiency can mimic atypical hemolytic uremic syndrome (aHUS), presenting with nonimmune hemolysis, thrombocytopenia, and acute kidney injury—measure erythrocyte G6PD concentrations in patients with suspected aHUS. 9

• The X-linked inheritance pattern means hemizygous males are typically affected, but females with extreme X-chromosome inactivation skewing can present with chronic hemolytic anemia. 7

• Neonatal jaundice in G6PD deficiency is likely due to impaired liver function rather than solely hemolysis. 10

• G6PD deficiency shows remarkable geographic correlation with malaria endemicity, representing a balanced polymorphism through heterozygote protection from malaria mortality. 410