890 ERVTHROCYTE PROTOPORPHYRIN (EP) IN THE NEWBORN-INCREASED RATIO OF FREE TO ZINC COMPLEXED EP IN YOUNG RBC

EP exists in both the free state (FEP) and in a zinc complexed form (ZEP) in RBC. The ratio of FEP to ZEP in healthy individuals averages 1:10. In the newborn period and in conditions with increased RBC turnover the FEP/EP ratio becomes elevated. Using dextran or stractan gradients, cord blood was centrifugally separated into 4 fractions known to contain RBC populations of different ages. The characteristics of these fractions and their EP contents are as follows: (N=6, EP expressed as μg/dl RBC). The total content of EP did not vary significantly according to RBC age but there was an increased FEP/EP in the fraction of younger, reticulocyte-rich cells. This EP pattern suggests that the newly formed EP is in the free state and may become zinc complexed or lost from RBC with time. The previous observation of an elevation in the free form of EP in hemolytic disorders is likely to be related to the presence of a larger percent of young RBC.