Levels of Lead in Blood and Hematocrit: Implications for the Evaluation of the Newborn and Anemic Patient

Extract: The uptake of lead was evaluated in vitro at hematocrits between 1% and 65% and at concentrations of lead in blood up to 1,000 μg/100 ml. Total erythrocyte volume was not a significant limiting factor in uptake of lead by erythrocytes at levels of lead in blood below 250 μg/100 ml at hematocrit 25%, below 375 μg/100 ml at hematocrit 41%, and below 500 μg/100 ml at hematocrit 65%. At a level of lead in blood of 80 μg/100 ml, erythrocyte volume was not a limiting factor at hematocrits above 10%. The diffusion of lead from a compartment which contained plasma or blood into another compartment which contained blood at hematocrits between 26% and 68% was studied. At equilibrium, the uptake of lead in blood was not reduced at the lower hematocrits.Lead was injected into rats with hematocrits between 31% and 68%, as a result of removal or transfusion of erythrocytes. Uptake of lead by blood did not correlate with hematocrit (significance of correlation coefficient >0.05). Rats were exposed to lead during gestation, lactation, and for a subsequent 4-month period. This resulted in a fourfold elevation of levels of lead in blood (38.9 ± 9.9 μg/100 ml as compared with control values of 9.6 ± 3.8 μg/100 ml). No correlation between hematocrit and levels of lead in blood could be established (correlation coefficient 0.20, P > 0.05). Lead acetate in doses of 50 μg and 75 μg was injected into the yolk sacs of 4-day chick embryos and lead in blood and hematocrit levels were determined 14 days later. Increasing amounts of injected lead resulted in increasing levels of lead in blood (9.0 ± 2.7 μg/100 ml in controls; 19.2 ± 7.4 μg/100 ml at 50 μg, and 32.5 ± 11.7 μg/100 ml at 75 μg). Despite the differences in levels of lead in blood, no relation between hematocrit and lead in blood was found (correlation coefficients of 0.25, P > 0.05 and 0.11, P > 0.05). Lead in maternal and newborn infant blood and hematocrit levels were determined. Despite the difference in hematocrit between infants (64.3% ± 9.8%) and mothers (37.5% ± 3.6%), there was no significant difference between levels of lead in infant blood (19.1 ± 7.6 μg/lOOml) and in maternal blood (17.0 ± 5.6 μg/100 ml). A positive correlation was found between levels of lead in infant and maternal blood (correlation coefficient of 0.58, P < 0.01). No correlation could be demonstrated between hematocrit and levels of lead in blood among infants (correlation coefficient 0.22, P >0.05) or among mothers (correlation coefficient 0.24, P > 0.05). Speculation: It has been assumed that the clinical evaluation of a given level of lead in blood requires correction for anemia. This was based on the assumption that the uptake of lead by the blood is limited by the reduced circulatory erythrocyte volume. This study has shown that the erythrocyte is present in considerable excess in the lead-erythrocyte interaction within the commonly encountered range of hematocrit and levels of lead in blood. This would indicate that hematocrit variation has little influence on uptake of lead by blood and that correction of levels of lead in blood for anemia is unnecessary. The presence of similar levels of lead in blood for neonates and mothers indicates that an equilibrium exists between levels of lead in fetal and maternal blood which is unaffected by the difference in fetal and maternal hematocrits. This suggests that the extent of lead exposure and the lead burden in soft tissue may be similar in the mother and fetus.