1 Department of Pediatrics, New York University Medical Center, New York, New York 10016
2 The New York City Department of Health, Bureau of Laboratories, New York, New York 10016
3 The New York City Department of Health, Bureau of Lead Poisoning Control, New York, New York 10016
Drs. McLaren et al. and Dr. Metcalf suggest that a threshold value of 250µg/100 ml RBC may be too high for a positive FEP. A threshold of 100µg/100 ml RBC, however, seems to us far too low since in children 1 to 6 years with blood Pb
20µg/100 ml the mean FEP level is higher (79 ± 26µg/100 ml RBC) than in adult males (47 ± 15µg/100 ml RBC). With a threshold of 160µg/100 ml RBC (= mean + 3 standard deviations), the FEP test identifies all samples with blood Pb
60µg/10O ml, 87% of those 50 to 59µg/100 ml, 72% of those 40 to 49µg/100 ml but also 14% of those
39µg/100 ml.