Use of zinc protoporphyrin measured by the Protofluor-Z hematofluorometer in screening children for elevated blood lead levels
P. B. Rolfe, J. F. Marcinak, A. J. Nice and R. H. Williams
Department of Pediatrics, University of Illinois, Chicago 60612.
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.
