The interpretation of zinc protoporphyrin changes in lead intoxication: a case report and review of the literature.

BACKGROUND Zinc protoporphyrin (ZPP) has been used both as a screening and diagnostic test for overexposure to lead for nearly 30 years, although limitations for both purposes are recognized. METHODS We present longitudinal findings for ZPP and whole-blood lead in a man with two episodes of acute lead intoxication and review the literature on the use of ZPP. RESULTS AND CONCLUSIONS ZPP elevations in both chronic and acute exposure settings lag behind elevations in whole-blood lead by approximately 8-12 weeks. Therefore, ZPP measurement, in conjunction with whole-blood lead determination, has clinical utility in cases of substantial overexposure by providing information on how long an individual may have been overexposed to lead. A guide to the interpretation of various combinations of whole-blood lead and ZPP results is provided. However, while ZPP levels do correlate with whole-blood lead measurements in aggregate, the considerable individual variability of ZPP measurements, poor sensitivity at lower ranges of lead exposure, poor specificity and delayed changes in unstable exposure conditions indicate that this test contributes little to screening programs. Finally, our results confirm that basophilic stippling is seen in acute as well as chronic lead intoxication, and may provide the first indication of lead intoxication.