Abstract • 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) References 1. Centers for Disease Control. Preventing Lead Poisoning in Young Children: A Statement by the Centers for Disease Control . Atlanta, Ga: US Department of Health and Human Services; 1985. Report 99-230. 2. Centers for Disease Control. Preventing Lead Poisoning in Young Children: A Statement by the Centers for Disease Control . Atlanta, Ga: US Department of Health and Human Services; 1991. Report 537-304. 3. McElvaine MD, Orbach HG, Binder S, Blanksma LA, Maes EF, Krieg RM. Evaluation of the erythrocyte protoporphyrin test as a screen for elevated blood lead levels . J Pediatr. 1991;119:548-550.Crossref 4. Stanton NV, Gunter EW, Parsons PJ, Field PH. Empirically determined lead-poisoning screening cutoff for the Protofluor-Z hematofluorometer . Clin Chem. 1989;35:2104-2107. 5. Fernandez FJ. Micromethod for lead determination in whole blood by atomic absorption, with use of the graphite furnace . Clin Chem. 1975;21: 558-561. 6. Erdreich LS, Lee ET. Use of relative operating characteristic analysis in epidemiology . Am J Epidemiol. 1981;114:649-662. 7. Parsons PJ, Reilly AA, Hussain A. Observational study of erythrocyte protoporphyrin screening test for detecting low lead exposure in children: impact of lowering the blood lead action threshold . Clin Chem. 1991;37: 216-225. 8. DeBaun MR, Sox HC. Setting the optimal erythrocyte protoporphyrin screening decision threshold for lead poisoning: a decision analytic approach . Pediatrics . 1991;88:121-131. 9. Turk DS, Schonfeld DJ, Cullen M, Rainey P. Sensitivity of erythrocyte protoporphyrin as a screening test for lead poisoning . N Engl J Med. 1992; 326:137-138. 10. Labbé RF, Rettmer RL. Measurement of zinc protoporphyrin with the Protofluor-Z system . Clin Chem. 1990;36:702-703. 11. Labbé RF, Rettmer RC, Shah AG, Turnlund JR. Zinc protoporphyrin: past, present and future . Ann N Y Acad Sci. 1987;514:7-14.Crossref 12. Shaltout AA, Guthrie R, Moussa M, et al. Erythrocyte protoporphyrin screening for lead poisoning in Bedouin children: a study from Kuwait . J Trop Pediatr. 1989;35:87-91.Crossref 13. Zwennis WCM, Franssen AC, Wijnans MJ. Use of zinc protoporphyrin in screening individuals for exposure to lead . Clin Chem. 1990;36:1456-1459. 14. Needleman HL, Jackson RJ. Lead toxicity in the 21st century: will we still be treating it? Pediatrics . 1992;89:678-680.
American Journal of Diseases of Children – American Medical Association
Published: Jan 1, 1993