The relationship between zinc protoporphyrin (ZPP) and “free” erythrocyte protoporphyrin (FEP) in lead-exposed individuals

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Abstract
The relationship between zinc protoporphyrin (ZPP) and total erythrocyte protoporphyrin, measured as “free” erythrocyte protoporphyrin (FEP), was determined in 194 adult subjects with different occupational and non-occupational lead exposures. Furthermore, the ZPP-FEP comparison was considered with respect to the dose-effect relationship of ZPP and FEP with blood lead (PbB) for males and females, respectively. Bilirubin (Bil.) interferences in ZPP analysis were taken into account. A very close and highly significant relationship (r=0.962, PPr=0.767 and 0.718; femalesr=0.525 and 0.405) was also found. It was established, by both in vitro and in vivo studies, that Bil. interferes with the ZPP fluorescence readings; the relationship between “false” positive ZPP concentrations and Bil. concentrations (in vitror=0.987, in vivor=0.903) was highly significant (Pr=0.948,P<0.001) influence of increased carboxyhemoglobin (COHb) concentrations on the decrease in hematofluorometer ZPP readings, due to inadequate oxygenation of the blood, was found. The results obtained confirm the usefulness of ZPP determinations using hematofluorometers for surveillance of increased lead absorption but stress that the interfering effect of Bil., and to a lesser extent of COW cannot be ignored.