[Biological indicators and reference values].

Abstract

For biological indicators of exposure, effect or susceptibility, appropriate reference values should be available for a comparative evaluation at individual or at group level. Reference values can be either measured in the same subjects before the exposure starts (internal reference), or extrapolated from an appropriately selected group (external reference). In both cases, confounding factors as well as possible sources of variability (biological and analytical), must be taken into account and controlled. Proceeding from clinical chemistry to occupational and environmental medicine, different exclusion and partition criteria in producing reference values should be adopted. Whereas clinical chemistry is aimed at discriminating people as having or not diseases, preventive medicine deals with healthy subjects to prevent effects derived from abnormal exposure to xenobiotics. To this purpose, it is mandatory that general requirements are satisfied, such as the clear definition of the reference population, the conditions under which the specimens were obtained, the adequacy of the indicator itself to provide information, provided that all laboratory results were produced by adequately standardized methods under sufficient quality control. Since we are shifting from macro to microdoses, reference values would help in discriminating natural or man-made sources of exposure.