What is the most common cause of increased red cell protoporphyrin level ?: (A) Iron deficiency, (B) Thiamine deficiency, (C) Reactive lymphocytosis, (D) Drug toxicity
Answer is A. The most common causes of increased red cell protoporphyrin levels are absolute or relative iron deficiency and lead poisoning. Reference: Harrisons Principles of Internal Medicine, 18th Edition, Page 847