This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Protoporphyrin levels >100 mg/dl indicates: 
Select and explain. 
A. Iron overload, B. Lead poisoning, C. Porphyria, D. All of the above
B: Lead poisoning
Answer: B: Lead poisoning 
Explanation: Protoporphyrin is an intermediate in the pathway to heme synthesis. Under conditions in which heme synthesis is impaired, protoporphyrin accumulates within the red cell. This reflects an inadequate iron supply to erythroid precursors to suppo haemoglobin synthesis. Normal values are <30 mg/dL of red cells. In iron deficiency, values in excess of 100 mg/dL are seen. The most common causes of increased red cell protoporphyrin levels are absolute or relative iron deficiency and lead poisoning. Ref: Harrison's principle of internal medicine 17th edition, chapter 98.