Zinc protoporphyrin IX
|Molar mass||626.032 g/mol|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Zinc protoporphyrin (ZPP) is a compound found in red blood cells when heme production is inhibited by lead and/or by lack of iron.  Instead of incorporating a ferrous ion, to form heme, protoporphyrin IX, the immediate precursor of heme, incorporates a zinc ion, forming ZPP. The reaction to insert a ferrous ion into protoporphyrin IX is catalyzed by the enzyme ferrochelatase.
Measurement of zinc protoporphyrin in red cells has been used as a screening test for lead poisoning. and for iron deficiency. There are a number of specific clinical situations in which this measurement has been found to be useful.
Zinc protoporphyrin levels can be elevated as the result of a number of conditions, for instance:
- lead poisoning
- iron deficiency
- sickle cell anemia
- sideroblastic anemia
- anemia of chronic disease
- vanadium exposure
- erythropoietic protoporphyria
The virtue of ZPP testing as a screen is that all of these conditions can be considered worth discovering.
The fluorescent properties of ZPP in intact red cells allows the ZPP/heme molar ratio to be measured quickly, at low cost, and in a small sample volume.
Porphyrin compounds containing zinc have been known since the 1930s. They became of more than academic interest with the discovery, in 1974, that ZPP was the major non-heme porphyrin formed in red cells as the result of lead poisoning or iron deficiency.
It was already known at this time that non-heme Protoporphyrin IX levels were elevated in these conditions, but prior investigators had used extraction methods that converted ZPP to unbound Protoporphyrin IX.
The early literature is sometimes confusing, and results are hard to compare without detailed examination of the measurement methods and the conversion factors used to report the results. Reports may refer to Free Erythrocyte Protoporphyrin (FEP) or Erythrocyte Protoporphyrin (EP or EPP). ZPP is also abbreviated ZP and ZnPP. Current practice is tending to measure and report the molar ratio of ZPP to Heme (μmole/mole).
- Labbé RF, Vreman HJ, Stevenson DK (December 1999). "Zinc protoporphyrin: A metabolite with a mission". Clinical Chemistry 45 (12): 2060–72. PMID 10585337.
- Martin CJ, Werntz CL, Ducatman AM (December 2004). "The interpretation of zinc protoporphyrin changes in lead intoxication: a case report and review of the literature". Occupational Medicine 54 (8): 587–91. doi:10.1093/occmed/kqh123. PMID 15576877.
- Verschoor M, Herber R, Zielhuis R, Wibowo A (1987). "Zinc protoporphyrin as an indicator of lead exposure: precision of zinc protoporphyrin measurements". International Archives of Occupational and Environmental Health 59 (6): 613–21. doi:10.1007/BF00377923. PMID 3679557.
- Crowell R, Ferris AM, Wood RJ, Joyce P, Slivka H (July 2006). "Comparative effectiveness of zinc protoporphyrin and hemoglobin concentrations in identifying iron deficiency in a group of low-income, preschool-aged children: practical implications of recent illness". Pediatrics 118 (1): 224–32. doi:10.1542/peds.2006-0156. PMID 16818569.
- Blumberg WE, Eisinger J, Lamola AA, Zuckerman DM (February 1977). "The hematofluorometer". Clinical Chemistry 23 (2 PT. 1): 270–4. PMID 832391.
- Lamola AA, Yamane T (December 1974). "Zinc protoporphyrin in the erythrocytes of patients with lead intoxication and iron deficiency anemia". Science 186 (4167): 936–8. doi:10.1126/science.186.4167.936. PMID 4469690.
- Piomelli S (June 1973). "A micromethod for free erythrocyte porphyrins: the FEP test". The Journal of Laboratory and Clinical Medicine 81 (6): 932–40. PMID 4710372.
- Some reports, for instance, measured the ZPP/Heme molar ratio (μmole ZPP per mole of heme), but reported this as the weight concentration (μg of EP per deciliter of packed red cells, or μg of EP per g hemoglobin at an assumed hematocrit of 35), and sometimes without easy access to the assumptions used in the conversion.