Blood zinc protoporphyrin is elevated only in sickle cell patients with low fetal hemoglobin

Increased levels of various porphyrin species have been reported in sickle cell anemia (SS) patients in the absence of lead poisoning and iron deficiency anemia, but conflicting data remain. Suspecting that SS patients may be heterogenous for this abnormality, we have studied zinc protoporphyrin (ZPP) and protoporphyrin IX (PPIX) blood levels and find abnormally elevated levels of ZPP in those with low peripheral fetal hemoglobin (%HbF) levels. Two groups exist: one with <9% HbF and elevated ZPP, and one with ≥9% HbF and normal ZPP levels (P < 8.1 × 10⁻⁴). There is a strong negative correlation of ZPP levels with %Hb F (r = –0.83, P < 8.0 × 10⁻⁵), and a moderate one with total hemoglobin levels (r = –0.55, P < 0.05). These results suggest that ZPP may indeed contribute to the pathophysiology of the disease and/or serve as a marker of the severity of the disease.