Trace elements in human clinical specimens: evaluation of literature data to identify reference values.

Reference values are proposed for the concentrations of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Pb, Se, and Zn in whole blood, blood serum, urine, milk, liver, and hair from adult human subjects. For F, I, and Ni, it was not possible to evaluate reference intervals for all the specimens mentioned above. For several elements, including Al, B, Br, Cs, Li, Rb, U, and V, the present status of the literature does not provide an adequate basis for formulating baseline concentrations; therefore, results from selected investigations are listed for information only. For elements such as Cu, Fe, and Zn, which are known to be homeostatically controlled, the concentrations in whole blood and blood serum follow a gaussian-like frequency distribution, and we could consider both median and mean values for evaluation. On the other hand, elements whose concentrations in tissues and body fluids are influenced by dietary availability (e.g., As and Se) or environmental factors (e.g., Cd, Hg, and Pb) show wide scatter. In these cases, the median appeared to be a better indicator of the central tendency than the mean, when different populations are involved. These points are illustrated.