Use of zinc protoporphyrin measured by the Protofluor-Z hematofluorometer in screening children for elevated blood lead levels.

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 mumol/L and 8% had lead levels of at least 1.21 mumol/L. The sensitivity, positive predictive value, and negative predictive value of a zinc protoporphyrin level of 70 mumol/mol of hemoglobin for detecting a lead level of 0.48 mumol/L were 42%, 66%, and 50%, respectively, and for a lead level of 1.21 mumol/L were 74%, 18%, and 97%, respectively. Receiver operating characteristic curves demonstrated that for detecting lead levels of 0.48 mumol/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.