Table 2.

Human <5 μg/dL. Summary of key studies in humans outlining the neurodevelopmental, cognitive, and achievement outcomes of blood lead levels below 5 μg/dL reported at p< .05. Excludes studies not explicitly reporting blood lead levels. Blood lead levels are listed as averages, unless otherwise noted, and appear as reported in respective studies. The most conservative adjusted statistical outcomes available are presented. Inclusion/exclusion criteria were established to determine study selection.¹

Test	Outcome (Using adjusted scores when available)	Mean Blood Lead Level (μg/dL)	Design	Age of Testing	Reference
<5 μg/dL, Human
I. Verbal Processing/Memory
Color Naming Task; Information Processing Speed	NS	<3.0 μg/dL	n=237 One test point Regression analysis using quartiles	7.5 yrs	Chiodo et al., 2004
			No reference group
Color Naming Task; Information Processing Speed	Deficits	<5.0 μg/dL
WRAML; Verbal Memory Index	NS	3–4.0 μg/dL	n=389 One test point 1–2 μg/dL, reference group	6–10 yrs	Surkan et al., 2007
II. Intelligence Scale/Achievement Test
WISC-III, Full-scale	NS	<5.0 μg/dL	n=237 One test point	7.5 yrs	Chiodo et al., 2004
			Regression analysis using quartiles
			No reference group
WISC-III, Full-scale	NS	3–4.0 μg/dL	n=389 One test point	6–10 yrs	Surkan et al., 2007
			1–2 μg/dL, reference group
WISC-IV, Short form & WIAT-II	Deficits	0.4–3.47 μg/dL	n=150 Cross-sectional; Case control	8–17 yrs	Nigg et al., 2008
			Regression-based path analysis
			No reference group
WISC- III, Performance	NS	<3.0 μg/dL	n=237 One test point	7.5 yrs	Chiodo et al., 2004
			Regression analysis using quartiles
			No reference group
WISC-III, Performance	Deficits	<5.0 μg/dL
Stanford-Binet; Intelligence Scale	Deficits	<5.0 μg/dL	n=172 Longitudinal Nonlinear mixed model	24mos & 120 mos	Canfield et al., 2003
			No reference group
WISC-R, Block Design	NS	<5.0 μg/dL	n=4,853 Cross-sectional, NHANES-III	6–16 yrs	Lanphear et al., 2000
			Regression analysis using quartiles
			No reference group
WISC-III, Block Design	NS	<3.0 μg/dL	n=237 One test point	7.5 yrs	Chiodo et al., 2004
			Regression analysis using quartiles
			No reference group
WISC-III, Block Design	Deficits	<5.0 μg/dL
WISC-III Block Design	NS	3–4.0 μg/dL	n=389 One test point	6–10 yrs	Surkan et al., 2007
			1–2 μg/dL, reference group
WRAT-R; Reading Subset	Deficits	<5.0 μg/dL	n=4,853 Cross-sectional, NHANES-III	6–16 yrs	Lanphear et al., 2000
			Regression analysis using quartiles
			No reference group
WIAT, Reading Composite	NS	3–4.0 μg/dL	n=389 One test point	6–10 yrs	Surkan et al., 2007
			1–2 μg/dL, reference group
WRAT, Arithmetic	Deficits	<5.0 μg/dL	n=4,853 Cross-sectional, NHANES-III	6–16 yrs	Lanphear et al., 2000
			Regression analysis using quartiles
			No reference group
WISC-III, Arithmetic	NS	3–4.0 μg/dL	n=389 One test point 1–2 μg/dL, reference group	6–10 yrs	Surkan et al., 2007
III. Attention
Child Behavior Checklist-Attention Teacher Report Form	Deficits	<3.0 μg/dL	n=237 One test point Regression analysis using quartiles	7.5 yrs	Chiodo et al., 2004
			No reference group
Child Behavior Checklist-Attention Teacher Report Form	NS	<5.0 μg/dL
Barkley Inattention	Deficits	<3.0 μg/dL
Barkley Off-Task	NS	<3.0 μg/dL
Barkley Off-Task	Deficits	<5.0 μg/dL
Continuous Performance Test-Sustained Attention	NS	<5.0 μg/dL
Mental Rotation; Reaction Time	NS	<5.0 μg/dL
Catsys System; Reaction Time	Deficits	<3.0 μg/dL	n=110 Longitudinal Regression analysis No reference group	Birth & 4–6 yrs	Després et al., 2005
IV. Impulsivity/Perseverative Errors/Cognitive Flexibility
Stop Signal Reaction Time Task	Deficits	0.4–3.4 μg/dL	n=150 Cross-sectional; Case-control Regression-based path analysis No reference group	8–17 yrs	Nigg et al., 2008
Wisconsin Card Sorting Task	NS	3–4.0 μg/dL	n=389 One test point	6–10 yrs	Surkan et al., 2007
			1–2 μg/dL, reference group
Matching Familiar Figures; Match to Sample	NS	<3.0 μg/dL	n=237 One test point Regression analysis using quartiles	7.5 yrs	Chiodo et al., 2004
			No reference group
Matching Familiar Figures; Match to Sample	Deficits	<5.0 μg/dL
V. Withdrawn
Child Behavior Checklist-Withdrawn Teacher Report Form	Deficits	<3.0 μg/dL	n=237 One test point Regression analysis using quartiles No reference group	7.5 yrs	Chiodo et al., 2004
Child Behavior Checklist-Withdrawn Teacher Report Form	NS	<5.0 μg/dL
VI. Short-term Memory/Working Memory
WISC-R; Digit Span	NS	<5.0 μg/dL	n=4,853 Cross-sectional, NHANES-III	6–16 yrs	Lanphear et al., 2000
			Regression analysis using quartiles No reference group
WISC-III, Digit Span; Backwards	NS	<3.0 μg/dL	n=237 One test point Regression analysis using quartiles No reference group	7.5 yrs	Chiodo et al., 2004
Sternberg Short-Term Memory Task; Processing Speed	Deficits	<3.0 μg/dL
WISC-III, Digit Span; Backwards	Deficits	<5.0 μg/dL
Seashore Rhythm Test; Auditory Working Memory	Deficits	<5.0 μg/dL
WISC-III, Digit Span	Deficits	3–4.0 μg/dL	n=389 One test point 1–2 μg/dL, reference group	3–4 yrs	Surkan et al., 2007
VII. Visual-Motor
Beery Visual-Motor Integration	NS	<3.0 μg/dL	n=237 One test point Regression analysis using quartiles No reference group	7.5 yrs	Chiodo et al., 2004
Beery Visual-Motor Integration	Deficits	<5.0 μg/dL
Bruininks-Oseretsky; Visual-Motor Control	NS	Neonatal Day 10: 4.8 μg/dL	One test point 1–2 μg/dL, reference group	6–10 yrs	Surkan et al., 2007
VIII. Dexterity/Balance
Catsys System; Balance	Deficits	4.1 μg/dL	n=110 Longitudinal Regression analysis No reference group	Birth & 4–6 yrs	Després et al., 2005
Catsys System; Pointing Movements	Deficits
IX. ADHD
DSM-IV Criteria for ADHD	Association	lst tertile: 0.2–0.8 μg/dL 2nd tertile: 0.9–1.3 μg/dL 3rd tertile: >1.3 μg/dL	n=2,588 Cross-sectional; NHANES (2001–2004) Regression analysis using tertiles No reference group	8–15 yrs	Froehlich et al., 2009
DSM-IV Criteria for ADHD-Combined	Association	3.4 μg/dL	n=150 Cross-sectional; Case-control Regression-based path analysis No reference group	8–17 yrs	Nigg et al., 2008
DSM-IV Criteria for ADHD, Hyperactivity-Impulsivity Symptoms	Association
DSM-IV Criteria for ADHD, Inattention-Disorganized Symptoms	NS
DSM-IV Criteria for ADHD-Combined	Association	0.3–2.2 μg/dL	n=150 Cross-sectional; Case-control Regression-based path analysis	6–17 yrs	Nigg et al., 2010
DSM-IV Criteria for ADHD-Predominantly Inattentive	NS
DSM-IV Parent Report of Child's ADHD Symptoms (KSADS); Hyperactivity-Impulsivity	Association
DSM-IV Parent Report of Child's ADHD Symptoms (KSADS); Inattention	NS
DSM-IV Parent Report of Child's Cognition & Hyperactivity-Impulsivity (Conners)	Association
DSM-IV Teacher Report of Child; ADHD Rating Scale & Inattention or Hyperactivity-Impulsivity	NS
DSM-IV Teacher Report of Child's Cognition (Conners)	Association
DSM-IV Teacher Report of Child's Hyperactivity & Impulsivity (Conners)	NS
DSM-IV criteria for ADHD & ADHD-Combined	Increased incidence	lst tertile: 0.2–0.8 μg/dL 2nd tertile: 0.9–1.3 μg/dL 3rd tertile: >1.3 μg/dL	n=2,588 Cross-sectional, NHANES (2001–2004) Regression analysis using tertiles No reference group	8–15 yrs	Froehhch et al., 2009
ADHD Assessed By Parent-Reported Medical Diagnosis of ADHD for Child & Child's Current Use of Stimulant Medication Use	Increased incidence (4.5-fold)	Lowest quintile (<0.7 μg/dL)vs Highest quintile (2–5.0 μg/dL)	n=4,704 Cross-sectional, NHANES (1999–2002) Dose response measure 0.7 μg/dL or less, reference group	4–15 yrs	Braun et al., 2006
X. Conduct Disorder
DSM-IV Criteria for Conduct Disorder	Increased incidence	1st quartile: 0.2–0.7 μg/dL 2nd quartile: 0.8–1.0 μg/dL 3rd quartile: 1.1–1.4 μg/dL 4th quartile: 1.5–10 μg/dL	n=3,081 Cross-sectional, NHANES (2001–2004) Regression analysis using quartiles No reference group	8–15 yrs	Braun et al., 2008

Abbreviations: ADHD=Attention Deficit Hyperactivity Disorder; DSM-IV=Diagnostic and Statistical Manual of Mental Disorder; KSADS=Kiddie Schedule for Affective Disorders and Schizophrenia; MOS=Months; NHANES III=National Health and Nutrition Examination Survey III Version; NHANES (2001 −2004)=National Health and Nutrition Examination Survey 2001–2004 Version; NS=Not Significant; WIAT=Wechsler Individual Achievement Test; WIAT-II=Wechsler Individual Achievement Test II Version; WISC-III=Wechsler Intelligence Scale for Children III Version; WISC-IV=Wechsler Intelligence Scale for Children IV Version; WISC-R=Wechsler Intelligence Scale for Children-Revised; WRAML=Wide Range Assessment of Memory and Learning; WRAT=Wide Range Achievement Test; WRAT-R=Wide Range Achievement Test Revised; YRS=Years