Policy Changes and Child Blood Lead Levels by Age 2 Years for Children Born in Illinois, 2001-2014.

To evaluate how lowering the blood lead level (BLL) intervention threshold affects childhood lead testing policy. We geocoded 4.19 million Illinois lead testing records (2001-2016) and linked to 2.37 million birth records (2001-2014), data on housing age, industrial emissions, and roads. We used multinomial logistic regression to determine predictors of BLLs of 10 micrograms per deciliter (µg/dL) or greater, 5 to 9 µg/dL, and 4 µg/dL. We found that 2.2% of children had BLLs of 10 µg/dL or greater, 8.9% had BLLs of 5 to 9 µg/dL, and 5.7% had BLLs of 4 µg/dL. Pre-1930 housing was associated with more than 2- to 4-fold increased relative risk of BLLs above all thresholds. Housing built in 1951 to 1978 was associated with increased relative risk of BLLs of 5 to 9 µg/dL (relative risk ratio [RRR] = 1.14; 95% confidence interval [CI] = 1.06, 1.21) but not with increased relative risk of BLLs of 10 µg/dL or greater (RRR = 0.99; 95% CI = 0.84, 1.16). At a given address, previous BLLs of 5 to 9 µg/dL or BLLs of 10 µg/dL or greater were associated with increased risk of BLLs of 5 to 9 µg/dL or BLLs of 10 µg/dL or greater among current occupants by 2.37- (95% CI = 2.20, 2.54) fold and 4.08- (95% CI = 3.69, 4.52) fold, respectively. The relative importance of determinants of above-threshold BLLs changes with decreasing intervention thresholds. States may need to update lead screening guidelines when decreasing the intervention threshold.