Lead and kidney: Concentrations, variabilities, and associations across the various stages of glomerular function

Data (N = 9882) from National Health and Nutrition Examination Survey for 2003-2014 for US adults aged ≥20 years were analyzed to evaluate the variabilities in concentrations of blood and urine lead across various stages of glomerular function. Those who had estimated glomerular filtration rate (eGFR) >90 mL/min/1.73 m² were defined to be in glomerular function stage 1 (GF-1), those who had eGFR between 60 and 90 mL/min/1.73 m² were defined to be in GF-2, those who had eGFR between 45 and 60 mL/min/1.73 m² were defined to be in GF-3A, those who had eGFR between 15 and 45 mL/min/1.73 m² were defined to be in GF-3B/4. There were consistent increases in adjusted geometric means (AGM) for both blood and urine lead from GF-1 to GF-3A even though increases were not uniform from one GF stage to another. For the total population, AGMs for blood lead were 1.23, 1.78, 2.25, and 2.25 μg/dL for GF-1, GF-2, GF-3A, and GF-3B/4 respectively. AGMs for urine lead were 0.49, 0.61, 0.68, and 0.47 μg/L for GF-1, GF-2, GF-3A, and GF-3B/4 respectively. Thus, from GF-3A to GF-3B/4, AGMs for both blood and urine lead decreased. However, percent increases from GF-1 to GF-3A for urine lead were smaller than for blood lead and percent decreases from GF-3A to GF-3B/4 for urine lead were larger than for blood lead. Females had lower AGMs than males for both blood and urine lead. Also, smoker-nonsmoker differences for blood lead narrowed as kidney function deteriorated but smoker-nonsmoker differences for urine cadmium lead as kidney function deteriorated. Smokers had sharper increases in AGMs for blood and urine lead than nonsmokers from GF-1 to GF-3A but at GF-3B/4, this difference was reduced to 0.17 μg/dL.