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. 2005 Jun 27;113(11):1509–1515. doi: 10.1289/ehp.7927

Table 3.

Linear regression models of uric acid, evaluating effect modification by ALAD genotype on associations of blood and tibia lead in two groups of lead workers, dichotomized by median age (40.6 years).

Panel 1: age < 40.6 years
Panel 2: age ≥ 40.6 years
Panel 3: age ≥ 40.6 years
Variable β-Coefficient SE β p-Value β-Coefficient SE β p-Value β-Coefficient SE β p-Value
Blood lead models
 Intercept 4.4070 0.1776 < 0.01 4.7507 0.1108 < 0.01 4.5906 0.1078 < 0.01
 Age (years) −0.0348 0.0084 < 0.01 −0.0123 0.0098 0.21 −0.0188 0.0098 0.06
 Systolic blood pressure (mm Hg) — — — — — — 0.0046 0.0027 0.09
 Serum creatinine (mg/dL) — — — — — — 2.4921 0.3799 < 0.01
 ALAD1-2 −0.2619 0.1591 0.10 −0.0292 0.1776 0.87 0.0870 0.1693 0.61
 Blood lead (μg/dL)a −0.0043 0.0040 0.27 0.0127 0.0040 < 0.01 0.0089 0.0038 0.02
 Blood lead × ALAD1-2b −0.0161 0.0134 0.23 −0.0212 0.0102 0.04 −0.0143 0.0098 0.14
Tibia lead models
 Intercept 4.3928 0.1746 < 0.01 4.7280 0.1075 < 0.01 4.6027 0.1074 < 0.01
 Age (years) −0.0335 0.0083 < 0.01 −0.0062 0.0096 0.52 −0.0157 0.0098 0.11
 Systolic blood pressure (mm Hg) — — — — — — 0.0059 0.0027 0.03
 Serum creatinine (mg/dL) — — — — — — 2.0767 0.4380 < 0.01
 ALAD1-2 −0.3553 0.2330 0.13 −0.1993 0.2013 0.32 −0.1180 0.1955 0.55
 Tibia lead (μg Pb/g bone mineral)a −0.0044 0.0020 0.03 0.0009 0.0013 0.48 0.0002 0.0013 0.89
 Tibia lead × ALAD1-2b −0.0047 0.0103 0.65 −0.0151 0.0079 0.06 −0.0138 0.0077 0.07
Truncated tibia lead modelsc
 Intercept 4.8218 0.1159 < 0.01 4.6499 0.1159 < 0.01
 Age (years) −0.0074 0.0103 0.48 −0.0160 0.0103 0.12
 Systolic blood pressure (mm Hg) — — — 0.0058 0.0028 0.04
 Serum creatinine (mg/dL) — — — 2.3661 0.4620 < 0.01
 ALAD1-2 −0.2763 0.2110 0.19 −0.1737 0.2033 0.39
 Tibia lead (μg Pb/g bone mineral)a 0.0079 0.0027 < 0.01 0.0063 0.0026 0.02
 Tibia lead × ALAD1-2b −0.0214 0.0084 0.01 −0.0193 0.0080 0.02

—, model shown was not adjusted for that covariate. Panels 1 and 2 display results in the younger and older groups, respectively. Panel 3 shows results in the older group after additional control for systolic blood pressure and serum creatinine. Models were also adjusted for sex, BMI, and alcohol use.

a

Reference category of homozygotes for the common gene allele (ALAD1-1).

b

p-Values for the cross-product terms reflect the statistical significance of the difference between the slopes of the regression line for the variant gene group and the regression line for the reference gene group; slopes in the variant gene group are obtained by adding the β-coefficient of the cross-product term to the β-coefficient for the reference category [i.e., the slope of the relation between blood lead and uric acid in those with ALAD1-2 genotype is −0.0085 in panel 2 (0.0127 + −0.0212)].

c

Tibia lead levels > 89 μg Pb/g bone mineral were removed from models.