The FEP test is a micromethod that measures rapidly and reliably free erythrocyte porphyrins in a blood sample of 20µl. The results of the FEP test increase exponentially with the blood Pb level.
The FEP test was performed in 1,038 blood specimens submitted to the New York City Department of Health Bureau of Laboratories for Pb analysis. Of these, 568 had Pb levels ≥ 40µg/100 ml. The concentration of FEP was higher than 250µg/100 ml RBC (positive FEP test) in all the samples with greatly increased blood Pb level (≥ 60µg/100 ml), in 55.1% of those with ambiguous blood Pb level (40 to 59µg/100 ml), and in 5.1% of those with low Pb level (< 40µg/100 ml).
The FEP test provides a biological indicator of undue lead absorption, suitable for rapid screening of children for lead poisoning. The test can easily be performed by any clinical laboratory.