A worker in a smelting factory develops colicky abdominal pain, constipation, wrist drop, bluish line at the gingival margin, and punctate basophilic stippling of red blood cells. Urine ALA excretion is markedly elevated. The MOST specific diagnostic marker for this condition is:
- A 24-hour urine delta-aminolevulinic acid (ALA) combined with blood lead level ✓
- B Whole blood lead level >10 µg/dL by atomic absorption spectrophotometry
- C Erythrocyte protoporphyrin levels alone
- D Urine coproporphyrin levels alone
Explanation
Lead poisoning inhibits two key enzymes in haem synthesis: ALA dehydratase (leading to ALA accumulation) and ferrochelatase (leading to protoporphyrin accumulation). The most diagnostically specific combination is blood lead level (confirming exposure) with 24-hour urine ALA (functional biomarker reflecting enzyme inhibition severity). Basophilic stippling reflects abnormal ribosomal clumping from lead-inhibited nucleotidase. Blood lead alone is the gold standard for screening; ALA confirms biological effect. Erythrocyte protoporphyrin and urine coproporphyrin are supportive but less specific.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
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Written and medically reviewed by the StethoPrep medical team.