Zinc Protoporphyrin
Overview
Zinc protoporphyrin (ZPP) is a fluorescent compound formed when zinc is incorporated into protoporphyrin IX due to reduced ferrochelatase activity and iron deficiency in erythropoietic cells. It accumulates in erythrocytes as an indicator of functional iron deficiency for hemoglobin synthesis, reflecting impaired heme production in bone marrow reticulocytes. Elevated ZPP levels indicate iron deficiency anemia, lead poisoning, or erythropoietic protoporphyria, while normal levels suggest adequate iron availability. Clinically, ZPP testing provides a sensitive, non-fasting screening tool for iron deficiency and lead toxicity, particularly useful in children and field screening settings.
Clinical Use Cases
- Screening for iron deficiency anemia in children, pregnant women, and at-risk populations.
- Lead poisoning diagnosis and monitoring chelation therapy.
- Assessment of functional iron deficiency in chronic inflammation or renal disease.
- Evaluation of anemias with impaired heme synthesis.
- Field screening where full iron studies are unavailable.
Specimen Types
- Whole blood (EDTA or heparin).
- Fingerstick capillary blood.
Measurement Methods
- Hematofluorometry (front-face fluorometry).
- High-performance liquid chromatography (HPLC).
- Flow cytometry.
- Laser scanning in vivo (HEMOQUANT).
Test Preparation and Influencing Factors
- No fasting required.
- Recent iron supplementation lowers ZPP within 4-6 weeks.
- Lead exposure inhibits ferrochelatase, elevating ZPP independently of iron status.
- Chronic inflammation or infection increases ZPP despite normal ferritin.
- Bilirubin or hemolysis interferes with fluorescence measurements.
- Recent blood transfusion transiently normalizes ZPP.
Synonyms
- ZPP.
- Erythrocyte protoporphyrin.
- Free erythrocyte protoporphyrin (FEP, older terminology).