The relationship between cadmium in kidney and cadmium in urine and blood in an environmentally exposed population

IntroductionCadmium (Cd) is toxic to the kidney and a major part of the body burden occurs here. Cd in urine (U-Cd) and blood (B-Cd) are widely-used biomarkers for assessing Cd exposure or body burden. However, empirical general population data on the relationship between Cd in kidney (K-Cd), urine, and blood are scarce. Our objectives were to determine the relationship between cadmium in kidney, urine, and blood, and calculate the elimination half-time of Cd from the kidney.MethodsKidney cortex biopsies, urine, and blood samples were collected from 109 living kidney donors. Cd concentrations were determined and the relationships between K-Cd, U-Cd, and B-Cd were investigated in regression models. The half-time of K-Cd was estimated from the elimination constant.ResultsThere was a strong association between K-Cd and U-Cd adjusted for creatinine (rp = 0.70, p < 0.001), while the association with B-Cd was weaker (rp = 0.44, p < 0.001). The relationship between K-Cd and U-Cd was nonlinear, with slower elimination of Cd at high K-Cd. Estimates of the K-Cd half-time varied between 18 and 44 years. A K-Cd of 25 μg/g corresponds to U-Cd of 0.42 μg/g creatinine in overnight urine (U-Cd/K-Cd ratio: about 1:60). Multivariate models showed Cd in blood and urinary albumin as determinants for U-Cd excretion.DiscussionIn healthy individuals with low-level Cd exposure, there was a strong correlation between Cd in kidney and urine, especially after adjustment for creatinine. Urinary Cd was also affected by Cd in blood and urinary albumin. Previous estimates of the U-Cd/K-Cd ratio may underestimate K-Cd at low U-Cd.

► The first study of the relation between Cd in kidney, blood and urine at low U-Cd
► Simultaneous samples were collected from healthy kidney donors.
► There was a nonlinear relationship between cadmium in kidney and urine.
► Estimates of the kidney cadmium half-time were 18–44 years, depending on model used.
► Previous data seem to underestimate kidney cadmium at low urinary cadmium.