Trace element reference values in tissues from inhabitants of the European Union. IX. Harmonization of statistical treatment: blood cadmium in Italian subjects.

Obtaining reliable trace element reference values in tissues and fluids from inhabitants of the European Union relies on the availability of standardized and harmonized protocols for the statistical treatment of the data on trace element levels in general European populations. In this context, cadmium was measured in the blood (BCd) of 514 Italian inhabitants from the Lombardy region and the results statistically treated and presented according to a procedure which includes: simple descriptive statistics and graphical analysis such as stem and leaf and box-plot representations (average BCd levels were 0.62 microgram/l; geometric mean, 0.51 microgram/l; median, 0.50 microgram/l; mode, 0.30 microgram/l; 95th percentile, 1.48 micrograms/l; 5th percentile, 0.20 microgram/l); p-p plot, Shapiro-Wilk and Lilliefors tests for normality (the distribution of the data is closer to the log-normal distribution and inconsistent with the hypothesis of normality); analysis of variance (BCd increases from 20 to about 60 years and then decreases; it is influenced by smoking but not by body mass and alcohol consumption and it is higher in men than in women); and step wise multiple regression analysis (BCd is influenced by the number of cigarettes/day and the total dose of exposure, cigarettes/day multiplied by smoking years). Tentative reference intervals for BCd based on the log transformation of the data are 0.14-1.82 micrograms Cd/l (whole population); 0.16-1.94 micrograms Cd/l (male) and 0.13-1.66 micrograms Cd/l (female); 0.24-2.68 micrograms Cd/l (smokers); and 0.14-1.27 micrograms Cd/l (non-smokers).