Table 4

Linear regression modelling of renal outcomes with cross product terms for lead dose biomarkers/lead job duration and age in tertiles in all lead workers with outliers removed†

Variable	β coefficient	SE β	p value
†BUN, serum creatinine, measured creatinine clearance, and calculated creatinine clearance models were also adjusted for age, gender, BMI, current/former exposure status, and hypertension. NAG and RBP models were adjusted for age, gender, BMI, systolic blood pressure, current/former exposure status, current alcohol ingestion, and diabetes. The youngest age tertile is the reference. p values for the cross product terms of the middle or oldest age categories with the lead measures reflect the statistical significance of the difference between the slopes of the regression line in that age category and the regression line for the youngest age group. Slopes in the non-reference categories are obtained by adding the beta coefficient of the cross product term to the beta coefficient for the reference category.
BUN (mg/dl) models
Intercept	14.3380	0.1503	<0.01
Age, years	0.0882	0.0140	<0.01
Tibia lead, μg Pb/g bone mineral	−0.0103	0.0085	0.23
Tibia lead*agecat2	−0.0021	0.0107	0.85
Tibia lead*agecat3	0.0165	0.0096	0.09
Intercept	14.3530	0.1509	<0.01
Age, years	0.0783	0.0145	<0.01
Blood lead, μg/dl	−0.0218	0.0157	0.17
Blood lead*agecat2	0.0091	0.0223	0.68
Blood lead*agecat3	0.0615	0.0214	<0.01
Intercept	14.4267	0.1547	<0.01
Age, years	0.0890	0.0149	<0.01
DMSA chelatable lead, μg Pb/g creatinine	−0.0002	0.0004	0.60
DMSA chelatable lead*agecat2	−0.0003	0.0005	0.58
DMSA chelatable lead*agecat3	0.0006	0.0005	0.28
Intercept	14.1352	0.2082	<0.01
Age, years	0.1078	0.0194	<0.01
Lead job duration, years	−0.1199	0.0645	0.06
Lead job duration*agecat2	0.1170	0.0776	0.13
Lead job duration*agecat3	0.1484	0.0683	0.03
Serum creatinine (mg/dl) models
Intercept	0.9328	0.0046	<0.01
Age, years	0.0005	0.0004	0.22
Tibia lead, μg Pb/g bone mineral	−0.0005	0.0003	0.06
Tibia lead*agecat2	−0.0003	0.0003	0.37
Tibia lead*agecat3	0.0008	0.0003	<0.01
Intercept	0.9340	0.0046	<0.01
Age, years	0.0003	0.0004	0.51
Blood lead, μg/dl	−0.0002	0.0005	0.62
Blood lead*agecat2	−0.0004	0.0007	0.56
Blood lead*agecat3	0.0013	0.0007	0.06
Intercept	0.9351	0.0047	<0.01
Age, years	0.0008	0.0005	0.09
DMSA chelatable lead, μg Pb/g creatinine	−0.0000	0.0000	0.15
DMSA chelatable lead*agecat2	−0.0000	0.0000	0.34
DMSA chelatable lead*agecat3	0.0000	0.0000	0.31
Intercept	0.9295	0.0063	<0.01
Age, years	0.0011	0.0006	0.06
Lead job duration, years	−0.0029	0.0020	0.15
Lead job duration*agecat2	0.0022	0.0024	0.36
Lead job duration*agecat3	0.0028	0.0021	0.18
Measured creatinine clearance (ml/min) models
Intercept	122.8823	1.1689	<0.01
Age, years	−0.7016	0.1103	<0.01
Tibia lead, μg Pb/g bone mineral	0.1057	0.0661	0.11
Tibia lead*agecat2	0.0649	0.0837	0.44
Tibia lead*agecat3	−0.1334	0.0753	0.08
Intercept	122.1588	1.1940	<0.01
Age, years	−0.7388	0.1156	<0.01
Blood lead, μg/dl	0.0917	0.1242	0.46
Blood lead*agecat2	0.0539	0.1799	0.77
Blood lead*agecat3	0.0034	0.1710	0.98
Intercept	122.7379	1.2142	<0.01
Age, years	−0.6909	0.1170	<0.01
DMSA chelatable lead, μg Pb/g creatinine	0.0022	0.0035	0.54
DMSA chelatable lead*agecat2	−0.0038	0.0043	0.39
DMSA chelatable lead*agecat3	−0.0021	0.0041	0.62
Intercept	122.6602	1.6132	<0.01
Age, years	−0.7604	0.1531	<0.01
Lead job duration, years	0.3278	0.5060	0.52
Lead job duration*agecat2	0.5192	0.6061	0.39
Lead job duration*agecat3	−0.4382	0.5352	0.41
Calculated creatinine clearance (ml/min) models
Intercept	101.5733	0.5636	<0.01
Age, years	−1.2002	0.0525	<0.01
Tibia lead, μg Pb/g bone mineral	0.0214	0.0320	0.50
Tibia lead*agecat2	0.0519	0.0410	0.21
Tibia lead*agecat3	−0.0481	0.0362	0.18
Intercept	101.4901	0.5616	<0.01
Age, years	−1.1891	0.0539	<0.01
Blood lead, μg/dl	−0.0265	0.0584	0.65
Blood lead*agecat2	0.0526	0.0830	0.53
Blood lead*agecat3	−0.0271	0.0800	0.74
Intercept	101.5341	0.5756	<0.01
Age, years	−1.2315	0.0556	<0.01
DMSA chelatable lead, μg Pb/g creatinine	0.0017	0.0017	0.30
DMSA chelatable lead*agecat2	0.0006	0.0020	0.76
DMSA chelatable lead*agecat3	−0.0014	0.0019	0.46
Intercept	101.8421	0.7663	<0.01
Age, years	−1.2920	0.0714	<0.01
Lead job duration, years	0.2908	0.2392	0.22
Lead job duration*agecat2	−0.0047	0.2881	0.99
Lead job duration*agecat3	−0.1621	0.2532	0.52
ln NAG (ln [μmol/h/g creatinine]) models
Intercept	5.0814	0.0438	<0.01
Age, years	0.0166	0.0025	<0.01
Tibia lead, μg Pb/g bone mineral	0.0004	0.0014	0.75
Tibia lead*agecat2	0.0024	0.0017	0.16
Tibia lead*agecat3	0.0017	0.0016	0.28
Intercept	5.0769	0.0436	<0.01
Age, years	0.0154	0.0026	<0.01
Blood lead, μg/dl	0.0016	0.0025	0.52
Blood lead*agecat2	0.0063	0.0036	0.08
Blood lead*agecat3	0.0089	0.0035	0.01
Intercept	5.0857	0.0443	<0.01
Age, years	0.0155	0.0026	<0.01
DMSA chelatable lead, μg Pb/g creatinine	0.0000	0.0001	0.58
DMSA chelatable lead*agecat2	0.0002	0.0001	0.03
DMSA chelatable lead*agecat3	0.0002	0.0001	0.08
Intercept	5.0778	0.0505	<0.01
Age, years	0.0183	0.0033	<0.01
Lead job duration, years	−0.0040	0.0106	0.71
Lead job duration*agecat2	−0.0002	0.0126	0.99
Lead job duration*agecat3	0.0169	0.0112	0.13
ln RBP (ln [μg/g creatinine]) models
Intercept	3.4745	0.0546	<0.01
Age, years	0.0185	0.0031	<0.01
Tibia lead, μg Pb/g bone mineral	0.0027	0.0017	0.12
Tibia lead*agecat2	−0.0015	0.0022	0.49
Tibia lead*agecat3	−0.0028	0.0020	0.15
Intercept	3.4527	0.0545	<0.01
Age, years	0.0189	0.0032	<0.01
Blood lead, μg/dl	0.0044	0.0032	0.17
Blood lead*agecat2	−0.0035	0.0045	0.44
Blood lead*agecat3	−0.0030	0.0043	0.49
Intercept	3.4622	0.0548	<0.01
Age, years	0.0176	0.0033	<0.01
DMSA chelatable lead, μg Pb/g creatinine	0.0002	0.0001	0.03
DMSA chelatable lead*agecat2	−0.0000	0.0001	0.80
DMSA chelatable lead*agecat3	−0.0002	0.0001	0.14
Intercept	3.4920	0.0626	<0.01
Age, years	0.0164	0.0041	<0.01
Lead job duration, years	0.0134	0.0131	0.31
Lead job duration*agecat2	−0.0095	0.0157	0.55
Lead job duration*agecat3	−0.0084	0.0138	0.55