REFERENCE VALUES OF URINARY CHROMIUM IN ITALY

Objective: The paper describes the results of a polycentric study for the assessment of reference values of urinary chromium (U-Cr) in the I talian population. Method: A total of 890 subjects (58.3% males and 41 .7% females) were selected on the basis of standardized criteria in ei ght different areas of Italy. Urinary chromium was determined on morni ng spot samples collected using standardized procedures. The U-Cr was determined independently by three laboratories using an Electrothermic atomization-Atomic Absorption Spectrometry (ETA-AAS) method with a de tection limit of 0.05 mu g/l, adopting - for the statistical analysis - the median value of the results of the three laboratories. The betwe en-laboratories within-subjects standard deviation was 0.049 mu g/l. D ue to the high proportion (approx. 28%) of undetectable chromium level s, the geometric mean (GM) and geometric standard deviation (GSD) were estimated using a procedure of linear interpolation. The analysis of the effects of some variables (sex, age, center, residence, smoking an d drinking habits) on the U-Cr values was also performed, by multiple regression analysis after logarithmic transformation, using GM and SD. Results: The reference value of U-Cr was of 0.08 mu g/l as an estimat ed GM, whereas the expected distribution ranged from not detectable (n d) (95% CI = nd-0.06) to 0.24 mu g/l (95th percentile; 95% CI = 0.20-0 .31). Among the variables studied, only geographical area and sex sign ificantly influenced the U-Cr levels. In subjects selected in the prov inces of Bari and Venice values of U-Cr were significantly lower than those determined in subjects residing in other areas. Conclusions: Fro m our investigation the reference values for U-Cr were lower than thos e obtained in previous investigations. In addition it confirms a furth er reduction in U-Cr levels following the previous decline reported in the 1970s and 1980s. In over 20 years U-Cr values in the general popu lation dropped from values greater than 1 mu g/l to values between 0.5 and 0.2 mu g/l. The reasons of this progressive decline cannot be att ributed in our opinion to a reduced intake of the metal, but mainly to the improvement in analytical instrumentation and methods. A further decrease may be ascribed to a more accurate definition of the referenc e groups and to a better control of pre-analytical factors. Considerin g that the reference values for U-Cr are much lower than those determi ned some decades ago, toxicological studies in order to verify the sig nificance of biological limit values currently suggested for chromium seem to be necessary.