January 1993

Use of Zinc Protoporphyrin Measured by the Protofluor-Z Hematofluorometer in Screening Children for Elevated Blood Lead Levels

Author Affiliations

From the Departments of Pediatrics (Drs Rolfe and Marcinak) and pathology (Mr Nice and Dr Williams), University of Illinois at Chicago.

Am J Dis Child. 1993;147(1):66-68. doi:10.1001/archpedi.1993.02160250068020

• Objective.  —To determine the usefulness of zinc protoporphyrin, as measured by the Helena Protofluor-Z hematofluorometer, for detecting elevated lead levels.

Design.  —Observational, descriptive review of laboratory records from a university toxicology laboratory.

Setting.  —Inner-city university pediatric clinic and two affiliated community clinics in Chicago, Ill.

Patients.  —Seven hundred seventy-five children younger than 7 years with paired lead-zinc protoporphyrin results.

Measurements/Results.  —Fifty-six percent had lead levels of at least 0.48 μmol/L and 8% had lead levels of at least 1.21 μmol/L. The sensitivity, positive predictive value, and negative predictive value of a zinc protoporphyrin level of 70 μmol/mol of hemoglobin for detecting a lead level of 0.48 μmol/L were 42%, 66%, and 50%, respectively, and for a lead level of 1.21 μmol/L were 74%, 18%, and 97%, respectively. Receiver operating characteristic curves demonstrated that for detecting lead levels of 0.48 μmol/L with zinc protoporphyrin, the probability of a true-positive result is close to that of a false-positive one.

Conclusion.  —Zinc protoporphyrin is not a reliable screening test for detecting low blood lead levels.(AJDC. 1993;147:66-68)