The independent contribution of bone and erythrocyte lead to urinary lead among middle-aged and elderly men: The normative aging study

plasma is the component of blood from which lead is free to cross cell memb ranes and cause organ toxicity. Plasma lead levels, however, are extremely low and difficult to measure. Urinary lead originates from plasma lead that has been filtered at the glomerular level; thus, urinary lead adjusted for glomerular filtration rate serves as a proxy for plasma lead levels. In th is investigation we examined the interrelationships of lead levels in whole blood corrected by hematocrit [i.e., erythrocyte lead (EPb)], trabecular b one (TBoPb), cortical bone (CBoPb), and urine excreted over 24 hr (UPb); al l samples were obtained from 71 middle-aged and elderly men with no known o ccupational lead exposures. Lead was measured by graphite furnace atomic ab sorption spectroscopy (blood), K-X-ray fluorescence (bone), and inductively coupled plasma mass spectroscopy (urine). Lead levels were generally low, with mean EPb, TBoPb, and CBoPb values of 13.8, 31.1, and 21.7 mu g/g, resp ectively, and a median UPb value of 6.15 mu g/day. In generalized additive models adjusted for body weight and creatinine clearance rate, both EPb and bone lead variables remained independently and significantly associated wi th UPb. This finding suggests that bone influences plasma lead in a manner that is independent of the influence of erythrocytic lead on plasma lead. T hus, the superiority of bone lead over blood lead in predicting some chroni c forms of toxicity may be mediated through bone's influence on plasma lead . In addition, this study suggests that measurement of urinary lead might b e useful as a proxy for plasma lead levels in studies of lead toxicity.