Basophilic stippling
Summary
Basophilic stippling refers to small, dark-blue granules dispersed throughout the cytoplasm of red blood cells on Wright-Giemsa stain, representing aggregated ribosomal RNA/ribosomes. It is classically associated with lead poisoning, but also seen in thalassemias, sideroblastic anemia, and other conditions causing abnormal heme synthesis or RBC maturation.
Detail
Basophilic stippling results from the precipitation and aggregation of residual ribosomal RNA (rRNA) within red blood cells, giving a stippled or granular appearance under light microscopy with Wright-Giemsa stain. Normally, rRNA is degraded and cleared during erythrocyte maturation; its persistence indicates defective RNA degradation or impaired erythropoiesis.
Pathophysiology: Lead inhibits pyrimidine 5'-nucleotidase, an enzyme responsible for degrading rRNA during RBC maturation. This causes accumulation of rRNA, forming the characteristic stippled pattern. Lead also inhibits ferrochelatase and ALA dehydratase, contributing to microcytic anemia with findings of basophilic stippling.
Key associations/causes: - Lead poisoning (classic association) — presents with microcytic anemia, abdominal pain, neuropathy (wrist/foot drop), and in children, developmental delay/irritability. - Thalassemias (alpha and beta) — due to ineffective erythropoiesis. - Sideroblastic anemia — due to disordered heme synthesis. - Alcohol use/myelodysplastic syndromes. - Megaloblastic anemia (less commonly).
Clinical significance: On a peripheral blood smear, basophilic stippling in a patient with microcytic anemia should prompt evaluation for lead toxicity (check blood lead level) or thalassemia (hemoglobin electrophoresis). It is a useful diagnostic clue distinguishing lead poisoning from simple iron deficiency anemia, which does not typically show stippling.
High-yield exam point: Lead poisoning will show microcytic anemia + basophilic stippling + ringed sideroblasts + elevated free erythrocyte protoporphyrin, distinguishing it from iron deficiency anemia.
Sources
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- Goldman-Cecil Medicine
- Hematology: Basic Principles and Practice (Hoffman)
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