Blood lead (Pb) clearance (CbPb) and serum creatinine clearance (CsCr), a metric of glomerular filtration rate (GFR), were estimated in approximately 7,600 subjects from the NHANES (2009-2016). Median CbPb in adults was 0.04 L/day (5th-95th percentile range: 0.01-0.12). Linear regression models explained approximately 68% of variance in CbPb in adults, with >98% of explained variance attributed to CsCr. These results provide an improved quantitative understanding of the possible effects of reverse causality in the interpretation of studies of associations between blood Pb and decrements in GFR.