What threshold of urinary cadmium (Cd-U) is currently considered indicative of early renal tubular dysfunction in exposed adult populations?

Cd is a chemical element that is both genotoxic and carcinogenic at high concentrations in the human body. It is classified by the International Agency for Research on Cancer as potential, in Group I carcinogen (IARC, 1993, 2012). Cd has physical and chemical properties similar to those of zinc and calcium, enabling it to pass easily through biological tissues. In solutions, in the absence of organic ligands, its most common forms are Cd2+, CdSO40, CdCl+ and CdHCO3+ (IRSN, 2004). In air, it is often in particulate, oxide, sulfide or chloride form (IARC, 2012; WHO, 2000). Cd enters the human body via metabolic pathways through ingestion of food, drinking water, tobacco consumption or inhalation of contaminated air. Once present in the human body, it is mainly found in erythrocytes via metallothioneins (IARC, 1993).  The United States Environmental Protection Agency (USEPA, 2002) has estimated a cancer risk index (CR) of between 1E-06 and 1E-04.)
 For kidney function, blood creatinine and glomerular filtration rate (GFR) are often monitored. However, according to the work of Levey, A. S et al. (2003), blood creatinine is estimated at 1.2 mg/dL in adult men or 1.1 mg/dL in women; and a GFR of less than 60 mL/min/1.73 m2 indicates chronic renal failure.
The threshold for renal toxicity associated with certain drugs, such as aminoglycosides or chiotherapy, is often related to plasma concentration or cumulative dose. For example, a peak plasma concentration above 2 mg/L for gentamicin may increase the risk of nephrotoxicity (Matzke, G. R et al., 2009).

Urinary cadmium is an indicative of the early renal tubular dysfunction of the exposed adults mostly between the range of 2-5ug/g creatinine