METHODOLOGICAL CONSIDERATIONS FOR THE ACCURATE DETERMINATION OF LEAD IN HUMAN PLASMA AND SERUM

Studies which accurately measure plasma or serum lead (Pb) are needed to evaluate the 'biologically active' fraction of Pb in the circulatio n, and to clarify the role of plasma in the transportation of Pb betwe en different compartments of the body. We evaluated several methodolog ical aspects which influence the determination of Pb in plasma and ser um. Generally, venous blood was obtained by different sampling methods (routine and ultraclean) from 3 subjects without history of Pb exposu re. After centrifugation (800 g) for 10 min, the plasma or serum was a nalyzed by inductively coupled plasma-high-resolution mass spectrometr y (ICP-MS). Several evaluations were conducted, including 1) compariso n of an ultraclean serum collection method with a plasma collection me thod that used a commercial Vacutainer(R)-type tube for trace metal (E DTA anticoagulant); 2) the effect of whole blood standing time prior t o centrifugation on plasma or serum Pb concentration; and 3) compariso n of a method using commercial heparinized Vacutainer(R) tubes to an u ltraclean plasma sampling method that utilized a low-Pb heparin antico agulant. Plasma or serum iron (Fe) levels were also measured to evalua te hemolysis. The 3 subjects had whole blood Pb (blood-Pb) levels of 1 .8, 2.0, and 2.7 mu g/dl. Their corresponding ultraclean serum-Pb leve ls were 0.40%, 0.30%, and 0.48% of their whole blood-Pb levels, respec tively. By comparison, the EDTA Vacutainer(R) method plasma-Pb values were 1.7%, 1.5%, and 2.4% of whole blood-Pb, respectively. Whole blood standing (clotting) times of 15, 40, and 70 min before centrifugation resulted in increasing ultraclean serum-Pb levels of 0.21%, 0.81%, an d 1.2% of whole blood-Pb (1.8 mu g/dl), respectively. Whole blood stan ding time had no effect on plasma-Pb levels when heparin Vacutainers(R ) were used, or when a low-Pb heparin was used to obtain ultraclean pl asma. However, plasma collected using the commercial heparin Vacutaine r(R) method contained consistently higher and more variable Pb levels than samples collected using the ultraclean plasma-Pb method. Hemolysi s, when present, contributed significantly to both plasma-Pb and serum -Pb levels. In conclusion, plasma-Pb and serum-Pb levels are dependent upon methodologic processing techniques, including Pb contamination c ontrol, redistribution due to EDTA anticoagulant, hemolysis, and time dependency in sample processing. While true plasma-Pb and serum-Pb lev els by any method have yet to be defined, these data provide a methodo logical basis from which to investigate variation in Pb partitioning b etween whole blood and plasma within individuals. (C) 1998 Wiley-Liss, Inc.